From dfcd5e9b6a09d52cab26c4357eaed406ea27d5bf Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 21:42:51 +0000
Subject: [PATCH 01/24] Pass the isolationLevel from the SpannerClient down to
 operation

---
 Spanner/src/Connection/Grpc.php |  2 ++
 Spanner/src/Database.php        | 16 ++++++++++++++--
 Spanner/src/Instance.php        | 11 ++++++++++-
 Spanner/src/SpannerClient.php   | 17 +++++++++++++++--
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/Spanner/src/Connection/Grpc.php b/Spanner/src/Connection/Grpc.php
index a70de619bf69..182f68fc23e7 100644
--- a/Spanner/src/Connection/Grpc.php
+++ b/Spanner/src/Connection/Grpc.php
@@ -1111,6 +1111,8 @@ public function beginTransaction(array $args)
             $pdml = new PartitionedDml();
             $options->setPartitionedDml($pdml);
             $args = $this->addLarHeader($args, $this->larEnabled);
+        } elseif (isset($transactionOptions['isolationLevel'])) {
+            $options->setIsolationLevel($transactionOptions['isolationLevel']);
         }
 
         // NOTE: if set for read-only actions, will throw exception
diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 977aecc28207..4c2afa5a208a 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -37,6 +37,7 @@
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
 
@@ -191,6 +192,11 @@ class Database
      */
     private $returnInt64AsObject;
 
+    /**
+     * @var int
+     */
+    private int $isolationLevel;
+
     /**
      * Create an object representing a Database.
      *
@@ -209,6 +215,8 @@ class Database
      *        be returned as a {@see \Google\Cloud\Core\Int64} object for 32 bit
      *        platform compatibility. **Defaults to** false.
      * @param string $databaseRole The user created database role which creates the session.
+     * @param int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      */
     public function __construct(
         ConnectionInterface $connection,
@@ -220,7 +228,8 @@ public function __construct(
         ?SessionPoolInterface $sessionPool = null,
         $returnInt64AsObject = false,
         array $info = [],
-        $databaseRole = ''
+        $databaseRole = '',
+        $isolationLevel = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
     ) {
         $this->connection = $connection;
         $this->instance = $instance;
@@ -238,6 +247,7 @@ public function __construct(
         $this->databaseRole = $databaseRole;
         $this->directedReadOptions = $instance->directedReadOptions();
         $this->returnInt64AsObject = $returnInt64AsObject;
+        $this->isolationLevel = $isolationLevel;
     }
 
     /**
@@ -812,7 +822,9 @@ public function transaction(array $options = [])
         }
 
         // There isn't anything configurable here.
-        $options['transactionOptions'] = $this->configureTransactionOptions();
+        $options['transactionOptions'] = $this->configureTransactionOptions([
+            'isolationLevel' => $this->isolationLevel
+        ]);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,
diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index b8fa34e9f4cf..43accfdf10e9 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -126,6 +126,11 @@ class Instance
      */
     private $directedReadOptions;
 
+    /**
+     * @var int
+     */
+    private $isolationLevel;
+
     /**
      * Create an object representing a Cloud Spanner instance.
      *
@@ -148,6 +153,8 @@ class Instance
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions}
      *           If using the `replicaSelection::type` setting, utilize the constants available in
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions\ReplicaSelection\Type} to set a value.
+     * @param int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      */
     public function __construct(
@@ -168,6 +175,7 @@ public function __construct(
 
         $this->setLroProperties($lroConnection, $lroCallables, $this->name);
         $this->directedReadOptions = $options['directedReadOptions'] ?? [];
+        $this->isolationLevel = $options['isolationLevel'];
     }
 
     /**
@@ -530,7 +538,8 @@ public function database($name, array $options = [])
             isset($options['sessionPool']) ? $options['sessionPool'] : null,
             $this->returnInt64AsObject,
             isset($options['database']) ? $options['database'] : [],
-            isset($options['databaseRole']) ? $options['databaseRole'] : ''
+            isset($options['databaseRole']) ? $options['databaseRole'] : '',
+            isset($options['isolationLevel']) ? $options['isolationLevel'] : $this->isolationLevel,
         );
     }
 
diff --git a/Spanner/src/SpannerClient.php b/Spanner/src/SpannerClient.php
index 272e892e36a1..ed00f7fd2584 100644
--- a/Spanner/src/SpannerClient.php
+++ b/Spanner/src/SpannerClient.php
@@ -36,6 +36,7 @@
 use Google\Cloud\Spanner\Connection\LongRunningConnection;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Psr\Cache\CacheItemPoolInterface;
 use Psr\Http\StreamInterface;
 
@@ -138,6 +139,11 @@ class SpannerClient
      */
     private $directedReadOptions;
 
+    /**
+     * @var int
+     */
+    private $isolationLevel;
+
     /**
      * Create a Spanner client. Please note that this client requires
      * [the gRPC extension](https://cloud.google.com/php/grpc).
@@ -201,6 +207,8 @@ class SpannerClient
      *           **Defaults to** `true` (enabled).
      *     @type string $universeDomain The expected universe of the credentials. Defaults to
      *            "googleapis.com"
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @throws GoogleException If the gRPC extension is not enabled.
      */
@@ -218,7 +226,8 @@ public function __construct(array $config = [])
             'projectIdRequired' => true,
             'hasEmulator' => (bool) $emulatorHost,
             'emulatorHost' => $emulatorHost,
-            'queryOptions' => []
+            'queryOptions' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED,
         ];
 
         if (!empty($config['useDiscreteBackoffs'])) {
@@ -279,6 +288,7 @@ public function __construct(array $config = [])
         ]);
 
         $this->directedReadOptions = $config['directedReadOptions'] ?? [];
+        $this->isolationLevel = $config['isolationLevel'];
     }
 
     /**
@@ -558,7 +568,10 @@ public function instance($name, array $instance = [])
             $name,
             $this->returnInt64AsObject,
             $instance,
-            ['directedReadOptions' => $this->directedReadOptions]
+            [
+                'directedReadOptions' => $this->directedReadOptions,
+                'isolationLevel' => $this->isolationLevel
+            ]
         );
     }
 

From 3d096e4426790f28319268930ed50eda599eca4f Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 23:24:24 +0000
Subject: [PATCH 02/24] Add support for isolationLevel to the Database class

---
 Spanner/src/Connection/Grpc.php               | 4 +++-
 Spanner/src/Database.php                      | 9 +++++++--
 Spanner/src/Operation.php                     | 6 +++++-
 Spanner/src/Transaction.php                   | 2 ++
 Spanner/src/TransactionConfigurationTrait.php | 4 ++++
 5 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Spanner/src/Connection/Grpc.php b/Spanner/src/Connection/Grpc.php
index 182f68fc23e7..a5395dca5201 100644
--- a/Spanner/src/Connection/Grpc.php
+++ b/Spanner/src/Connection/Grpc.php
@@ -1111,7 +1111,9 @@ public function beginTransaction(array $args)
             $pdml = new PartitionedDml();
             $options->setPartitionedDml($pdml);
             $args = $this->addLarHeader($args, $this->larEnabled);
-        } elseif (isset($transactionOptions['isolationLevel'])) {
+        }
+
+        if (isset($transactionOptions['isolationLevel'])) {
             $options->setIsolationLevel($transactionOptions['isolationLevel']);
         }
 
diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 4c2afa5a208a..23edf2943666 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -810,6 +810,8 @@ public function snapshot(array $options = [])
      *           Session labels may be applied using the `labels` key.
      *     @type string $tag A transaction tag. Requests made using this transaction will
      *           use this as the transaction tag.
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @return Transaction
      * @throws \BadMethodCallException If attempting to call this method within
@@ -821,9 +823,8 @@ public function transaction(array $options = [])
             throw new \BadMethodCallException('Nested transactions are not supported by this client.');
         }
 
-        // There isn't anything configurable here.
         $options['transactionOptions'] = $this->configureTransactionOptions([
-            'isolationLevel' => $this->isolationLevel
+            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
         ]);
 
         $session = $this->selectSession(
@@ -948,6 +949,10 @@ public function runTransaction(callable $operation, array $options = [])
                 if (!isset($options['transactionOptions']['partitionedDml'])) {
                     $options['begin'] = $options['transactionOptions'];
                 }
+
+                if (!isset($options['transactionOptions']['isolationLevel'])) {
+                    $options['transactionOptions']['isolationLevel'] = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
+                }
             } else {
                 $options['isRetry'] = true;
             }
diff --git a/Spanner/src/Operation.php b/Spanner/src/Operation.php
index 6c8aeecace91..e9f4d9748994 100644
--- a/Spanner/src/Operation.php
+++ b/Spanner/src/Operation.php
@@ -25,6 +25,7 @@
 use Google\Cloud\Spanner\Connection\ConnectionInterface;
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Rpc\Code;
 use InvalidArgumentException;
 
@@ -455,6 +456,8 @@ public function read(
      *           `false`.
      *     @type array $begin The begin transaction options.
      *           [Refer](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#transactionoptions)
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @return Transaction
      */
@@ -463,7 +466,8 @@ public function transaction(Session $session, array $options = [])
         $options += [
             'singleUse' => false,
             'isRetry' => false,
-            'requestOptions' => []
+            'requestOptions' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
         ];
         $transactionTag = $this->pluck('tag', $options, false);
         if (isset($transactionTag)) {
diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index 3d740cac45f3..b7a1577e5777 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -98,6 +98,8 @@ class Transaction implements TransactionalReadInterface
      *
      *     @type array $begin The begin Transaction options.
      *           [Refer](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#transactionoptions)
+     *     @type int $isolationLevel level of Isolation for this transaction instance
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @param ValueMapper $mapper Consumed internally for properly map mutation data.
      * @throws \InvalidArgumentException if a tag is specified on a single-use transaction.
diff --git a/Spanner/src/TransactionConfigurationTrait.php b/Spanner/src/TransactionConfigurationTrait.php
index 31dfa76809c7..f0b6219174bf 100644
--- a/Spanner/src/TransactionConfigurationTrait.php
+++ b/Spanner/src/TransactionConfigurationTrait.php
@@ -152,6 +152,10 @@ private function configureTransactionOptions(array $options = [])
             $transactionOptions['excludeTxnFromChangeStreams'] = $options['excludeTxnFromChangeStreams'];
         }
 
+        if (isset($options['isolationLevel'])) {
+            $transactionOptions['isolationLevel'] = $options['isolationLevel'];
+        }
+
         return $transactionOptions;
     }
 

From a5bb0d4139da220426474d15f3e6f52821967e04 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 23:26:15 +0000
Subject: [PATCH 03/24] Update the Instance class

---
 Spanner/src/Instance.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index 43accfdf10e9..97fa56920444 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -539,7 +539,7 @@ public function database($name, array $options = [])
             $this->returnInt64AsObject,
             isset($options['database']) ? $options['database'] : [],
             isset($options['databaseRole']) ? $options['databaseRole'] : '',
-            isset($options['isolationLevel']) ? $options['isolationLevel'] : $this->isolationLevel,
+            $options['isolationLevel'] ?? $this->isolationLevel,
         );
     }
 

From e37fbcaaabaac209056fa390b3f9e839c82759d9 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 16 Apr 2025 21:40:43 +0000
Subject: [PATCH 04/24] Add configuration for Database

---
 Spanner/src/Database.php    | 21 +++++++++++++++++----
 Spanner/src/Instance.php    |  3 ++-
 Spanner/src/Transaction.php | 12 ++++++++++++
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 23edf2943666..772087ac9cbd 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -1647,11 +1647,12 @@ public function delete($table, KeySet $keySet, array $options = [])
      *           timestamp.
      *     @type Duration $exactStaleness Represents a number of seconds. Executes
      *           all reads at a timestamp that is $exactStaleness old.
-     *     @type bool $begin If true, will begin a new transaction. If a
+     *     @type bool|array $begin If true, will begin a new transaction. If a
      *           read/write transaction is desired, set the value of
      *           $transactionType. If a transaction or snapshot is created, it
      *           will be returned as `$result->transaction()` or
      *           `$result->snapshot()`. **Defaults to** `false`.
+     *           If $begin is an array {@see TransactionOptions}
      *     @type string $transactionType One of `SessionPoolInterface::CONTEXT_READ`
      *           or `SessionPoolInterface::CONTEXT_READWRITE`. If read/write is
      *           chosen, any snapshot options will be disregarded. If `$begin`
@@ -1696,12 +1697,16 @@ public function execute($sql, array $options = [])
                 $this->pluck('sessionOptions', $options, false) ?: []
             );
 
-        list(
+        [
             $options['transaction'],
             $options['transactionContext']
-        ) = $this->transactionSelector($options);
+        ] = $this->transactionSelector($options);
         $options = $this->addLarHeader($options, true, $options['transactionContext']);
 
+        if ($options['transactionType'] === SessionPoolInterface::CONTEXT_READWRITE && $this->isolationLevel) {
+            $options['transaction']['begin']['isolationLevel'] ??= $this->isolationLevel;
+        }
+
         $options['directedReadOptions'] = $this->configureDirectedReadOptions(
             $options,
             $this->directedReadOptions ?? []
@@ -1766,7 +1771,7 @@ public function mutationGroup()
      *           transactions.
      * }
      *
-     * @retur \Generator {@see \Google\Cloud\Spanner\V1\BatchWriteResponse}
+     * @return \Generator {@see \Google\Cloud\Spanner\V1\BatchWriteResponse}
      *
      * @throws ApiException if the remote call fails
      */
@@ -1910,6 +1915,8 @@ public function batchWrite(array $mutationGroups, array $options = [])
      *           Please note, if using the `priority` setting you may utilize the constants available
      *           on {@see \Google\Cloud\Spanner\V1\RequestOptions\Priority} to set a value.
      *           Please note, the `transactionTag` setting will be ignored as it is not supported for partitioned DML.
+     *     @type array $transactionOptions Transaction options.
+     *           {@see V1\TransactionOptions}
      * }
      * @return int The number of rows modified.
      */
@@ -1923,10 +1930,16 @@ public function executePartitionedUpdate($statement, array $options = [])
                 'partitionedDml' => [],
             ]
         ];
+
         if (isset($options['transactionOptions']['excludeTxnFromChangeStreams'])) {
             $beginTransactionOptions['transactionOptions']['excludeTxnFromChangeStreams'] =
                 $options['transactionOptions']['excludeTxnFromChangeStreams'];
         }
+
+        if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
+            $options['transactionOptions']['isolationLevel'] ??= $this->isolationLevel;
+        }
+
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
 
         $options = $this->addLarHeader($options);
diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index 97fa56920444..80fdd9a53177 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -32,6 +32,7 @@
 use Google\Cloud\Spanner\Connection\ConnectionInterface;
 use Google\Cloud\Spanner\Connection\IamInstance;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * Represents a Cloud Spanner instance
@@ -175,7 +176,7 @@ public function __construct(
 
         $this->setLroProperties($lroConnection, $lroCallables, $this->name);
         $this->directedReadOptions = $options['directedReadOptions'] ?? [];
-        $this->isolationLevel = $options['isolationLevel'];
+        $this->isolationLevel = $options['isolationLevel'] ?? IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
     }
 
     /**
diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index b7a1577e5777..6af89ce71f48 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -248,6 +248,18 @@ public function executeUpdate($sql, array $options = [])
                 . ' This option should be set at the transaction level.'
             );
         }
+
+        if (
+            $this->type() === self::TYPE_SINGLE_USE &&
+            isset($options['transaction']['begin']['isolationLevel']) ||
+            isset($options['transaction']['single_use']['isolationLevel'])
+        ) {
+            throw new ValidationException(
+                'The isolation level can only be applied to read/write transactions.'.
+                'Single use transactions are not read/write',
+            );
+        }
+
         $options = $this->buildUpdateOptions($options);
         return $this->operation
             ->executeUpdate($this->session, $this, $sql, $options);

From 98c856ff33159be0009ea58736e70da40f617849 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 20:27:41 +0000
Subject: [PATCH 05/24] Add tests for isolationLevel

---
 Spanner/src/Database.php                   |   9 +-
 Spanner/tests/System/TransactionTest.php   |   6 +
 Spanner/tests/Unit/DatabaseTest.php        | 140 +++++++++++++++++++++
 Spanner/tests/Unit/TransactionTypeTest.php |  10 +-
 4 files changed, 158 insertions(+), 7 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 772087ac9cbd..96b64c974f39 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -1697,13 +1697,13 @@ public function execute($sql, array $options = [])
                 $this->pluck('sessionOptions', $options, false) ?: []
             );
 
-        [
+        list(
             $options['transaction'],
             $options['transactionContext']
-        ] = $this->transactionSelector($options);
+        ) = $this->transactionSelector($options);
         $options = $this->addLarHeader($options, true, $options['transactionContext']);
 
-        if ($options['transactionType'] === SessionPoolInterface::CONTEXT_READWRITE && $this->isolationLevel) {
+        if (isset($options['transaction']['readWrite'])) {
             $options['transaction']['begin']['isolationLevel'] ??= $this->isolationLevel;
         }
 
@@ -1937,7 +1937,8 @@ public function executePartitionedUpdate($statement, array $options = [])
         }
 
         if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
-            $options['transactionOptions']['isolationLevel'] ??= $this->isolationLevel;
+            $beginTransactionOptions['transactionOptions']['isolationLevel'] =
+                $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel;
         }
 
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
diff --git a/Spanner/tests/System/TransactionTest.php b/Spanner/tests/System/TransactionTest.php
index 99b9931cb025..02f3558f2185 100644
--- a/Spanner/tests/System/TransactionTest.php
+++ b/Spanner/tests/System/TransactionTest.php
@@ -22,6 +22,7 @@
 use Google\Cloud\Core\Exception\ServiceException;
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\V1\DirectedReadOptions\ReplicaSelection\Type as ReplicaType;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * @group spanner
@@ -409,6 +410,11 @@ public function testRunTransactionILBWithMultipleOperations()
                         'id' => $id,
                         'name' => uniqid(self::TESTING_PREFIX),
                         'birthday' => new Date(new \DateTime)
+                    ],
+                    'transaction' => [
+                        'begin' => [
+                            'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+                        ]
                     ]
                 ]
             );
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index a63c361fc6a8..78b37d67c0f6 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -57,6 +57,7 @@
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
 use Google\Cloud\Core\Exception\ServiceException;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * @group spanner
@@ -970,6 +971,38 @@ public function testTransaction()
         $this->assertInstanceOf(Transaction::class, $t);
     }
 
+    public function testTransactionWithIsolationLevel()
+    {
+        $this->connection->beginTransaction(Argument::allOf(
+            Argument::withEntry('session', $this->session->name()),
+            Argument::withEntry(
+                'database',
+                DatabaseAdminClient::databaseName(
+                    self::PROJECT,
+                    self::INSTANCE,
+                    self::DATABASE
+                )
+            ),
+            Argument::withEntry('requestOptions', [
+                'transactionTag' => self::TRANSACTION_TAG,
+            ]),
+            Argument::withEntry('transactionOptions', [
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+            ])
+        ))
+            ->shouldBeCalled()
+            ->willReturn(['id' => self::TRANSACTION]);
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+
+        $t = $this->database->transaction([
+            'tag' => self::TRANSACTION_TAG,
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ]);
+        $this->assertInstanceOf(Transaction::class, $t);
+    }
+
     public function testTransactionNestedTransaction()
     {
         $this->expectException(\BadMethodCallException::class);
@@ -1258,6 +1291,34 @@ public function testExecute()
         $this->assertEquals(10, $rows[0]['ID']);
     }
 
+    public function testExecuteWithIsolationLevel()
+    {
+        $sql = 'SELECT * FROM Table';
+
+        $this->connection->executeStreamingSql(Argument::allOf(
+            Argument::withEntry('sql', $sql),
+            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']]),
+            Argument::withEntry('transaction', [
+                'begin' => [
+                    'readWrite' => [],
+                    'isolationLevel' => IsolationLevel::REPEATABLE_READ
+                ]
+            ])
+        ))->shouldBeCalled()->willReturn($this->resultGenerator());
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+
+        $res = $this->database->execute($sql, [
+            'transactionType' => SessionPoolInterface::CONTEXT_READWRITE,
+            'begin' => [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]
+        ]);
+        $this->assertInstanceOf(Result::class, $res);
+        $rows = iterator_to_array($res->rows());
+        $this->assertEquals(10, $rows[0]['ID']);
+    }
+
     public function testExecuteWithSingleSession()
     {
         $this->database->___setProperty('sessionPool', null);
@@ -1332,6 +1393,40 @@ public function testExecutePartitionedUpdate()
         $this->assertEquals(1, $res);
     }
 
+    public function testExecutePartitionedUpdateWithIsolationLevel()
+    {
+        $sql = 'UPDATE foo SET bar = @bar';
+        $this->connection->beginTransaction(Argument::allOf(
+            Argument::withEntry('transactionOptions', [
+                'partitionedDml' => [],
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+            ]),
+            Argument::withEntry('singleUse', false)
+        ))->shouldBeCalled()->willReturn([
+            'id' => self::TRANSACTION
+        ]);
+
+        $this->connection->executeStreamingSql(Argument::allOf(
+            Argument::withEntry('sql', $sql),
+            Argument::withEntry('transaction', [
+                'id' => self::TRANSACTION,
+            ]),
+            Argument::withEntry('transactionOptions', [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]),
+            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']])
+        ))->shouldBeCalled()->willReturn($this->resultGenerator(true));
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+        $res = $this->database->executePartitionedUpdate($sql, [
+            'transactionOptions' => [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]
+        ]);
+
+        $this->assertEquals(1, $res);
+    }
+
     public function testRead()
     {
         $table = 'Table';
@@ -2139,6 +2234,51 @@ public function testBatchWriteWithExcludeTxnFromChangeStreams()
         ]);
     }
 
+    public function testRunTransactionIsolationLevel()
+    {
+        $gapic = $this->prophesize(SpannerClient::class);
+
+        $sessName = SpannerClient::sessionName(self::PROJECT, self::INSTANCE, self::DATABASE, self::SESSION);
+        $session = new SessionProto(['name' => $sessName]);
+        $resultSet = new ResultSet(['stats' => new ResultSetStats(['row_count_exact' => 0])]);
+        $gapic->createSession(Argument::cetera())->shouldBeCalled()->willReturn($session);
+        $gapic->deleteSession(Argument::cetera())->shouldBeCalled();
+
+        $sql = 'SELECT example FROM sql_query';
+        $stream = $this->prophesize(ServerStream::class);
+        $stream->readAll()->shouldBeCalledOnce()->willReturn([$resultSet]);
+        $gapic->executeStreamingSql($sessName, $sql, Argument::that(function (array $options) {
+            $this->assertArrayHasKey('transaction', $options);
+            $this->assertNotNull($transactionOptions = $options['transaction']->getBegin());
+            $this->assertEquals(IsolationLevel::REPEATABLE_READ, $transactionOptions->getIsolationLevel());
+            return true;
+        }))
+            ->shouldBeCalledOnce()
+            ->willReturn($stream->reveal());
+
+        $database = new Database(
+            new Grpc(['gapicSpannerClient' => $gapic->reveal()]),
+            $this->instance,
+            $this->lro->reveal(),
+            $this->lroCallables,
+            self::PROJECT,
+            self::DATABASE
+        );
+
+        $database->runTransaction(
+            function (Transaction $t) use ($sql) {
+                // Run a fake query
+                $t->executeUpdate($sql);
+
+                // Simulate calling Transaction::commmit()
+                $prop = new \ReflectionProperty($t, 'state');
+                $prop->setAccessible(true);
+                $prop->setValue($t, Transaction::STATE_COMMITTED);
+            },
+            ['transactionOptions' => ['isolationLevel' => IsolationLevel::REPEATABLE_READ]]
+        );
+    }
+
     private function createStreamingAPIArgs()
     {
         $row = ['id' => 1];
diff --git a/Spanner/tests/Unit/TransactionTypeTest.php b/Spanner/tests/Unit/TransactionTypeTest.php
index d228794c863b..210d07a04d73 100644
--- a/Spanner/tests/Unit/TransactionTypeTest.php
+++ b/Spanner/tests/Unit/TransactionTypeTest.php
@@ -34,6 +34,7 @@
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\Transaction;
 use Google\Cloud\Spanner\V1\SpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
@@ -84,7 +85,8 @@ public function testDatabaseRunTransactionPreAllocate()
         $this->connection->beginTransaction(Argument::allOf(
             Argument::withEntry('singleUse', false),
             Argument::withEntry('transactionOptions', [
-                'readWrite' => []
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
             ])
         ))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
@@ -123,7 +125,8 @@ public function testDatabaseTransactionPreAllocate()
         $this->connection->beginTransaction(Argument::allOf(
             Argument::withEntry('singleUse', false),
             Argument::withEntry('transactionOptions', [
-                'readWrite' => []
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED,
             ])
         ))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
@@ -740,7 +743,8 @@ public function testDatabaseReadBeginReadWrite($chunks)
     public function testTransactionPreAllocatedRollback()
     {
         $this->connection->beginTransaction(Argument::withEntry('transactionOptions', [
-            'readWrite' => []
+            'readWrite' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
         ]))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
         $sess = SpannerClient::sessionName(

From d1432158622c8835d718035411b5f0d52ff8851a Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 20:34:55 +0000
Subject: [PATCH 06/24] Fix style issues

---
 Spanner/src/Transaction.php | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index 6af89ce71f48..dd7d3d76d4a0 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -249,13 +249,12 @@ public function executeUpdate($sql, array $options = [])
             );
         }
 
-        if (
-            $this->type() === self::TYPE_SINGLE_USE &&
+        if ($this->type() === self::TYPE_SINGLE_USE &&
             isset($options['transaction']['begin']['isolationLevel']) ||
             isset($options['transaction']['single_use']['isolationLevel'])
         ) {
             throw new ValidationException(
-                'The isolation level can only be applied to read/write transactions.'.
+                'The isolation level can only be applied to read/write transactions.' .
                 'Single use transactions are not read/write',
             );
         }

From a3f2c86c17980da72ed7c11ee466b962e2f30a97 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 21:47:19 +0000
Subject: [PATCH 07/24] Update the executePartitionUpdate method

---
 Spanner/src/Database.php            | 11 ++++++-----
 Spanner/tests/Unit/DatabaseTest.php | 26 +++++---------------------
 2 files changed, 11 insertions(+), 26 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 96b64c974f39..ac096d0a9cfa 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -40,6 +40,7 @@
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
+use InvalidArgumentException;
 
 /**
  * Represents a Cloud Spanner Database.
@@ -1923,6 +1924,11 @@ public function batchWrite(array $mutationGroups, array $options = [])
     public function executePartitionedUpdate($statement, array $options = [])
     {
         unset($options['requestOptions']['transactionTag']);
+
+        if (isset($options['transactionOptions']['isolationLevel'])) {
+            throw new InvalidArgumentException('Partitioned DML cannot be configured with an isolation level');
+        }
+
         $session = $this->selectSession(SessionPoolInterface::CONTEXT_READWRITE);
 
         $beginTransactionOptions = [
@@ -1936,11 +1942,6 @@ public function executePartitionedUpdate($statement, array $options = [])
                 $options['transactionOptions']['excludeTxnFromChangeStreams'];
         }
 
-        if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
-            $beginTransactionOptions['transactionOptions']['isolationLevel'] =
-                $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel;
-        }
-
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
 
         $options = $this->addLarHeader($options);
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index 78b37d67c0f6..dabbb3a4758b 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -58,6 +58,8 @@
 use Prophecy\PhpUnit\ProphecyTrait;
 use Google\Cloud\Core\Exception\ServiceException;
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
+use InvalidArgumentException;
+use Kreait\Firebase\Exception\Messaging\InvalidArgument;
 
 /**
  * @group spanner
@@ -1393,31 +1395,13 @@ public function testExecutePartitionedUpdate()
         $this->assertEquals(1, $res);
     }
 
-    public function testExecutePartitionedUpdateWithIsolationLevel()
+    public function testExecutePartitionedUpdateWithIsolationLevelShouldRaise()
     {
         $sql = 'UPDATE foo SET bar = @bar';
-        $this->connection->beginTransaction(Argument::allOf(
-            Argument::withEntry('transactionOptions', [
-                'partitionedDml' => [],
-                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
-            ]),
-            Argument::withEntry('singleUse', false)
-        ))->shouldBeCalled()->willReturn([
-            'id' => self::TRANSACTION
-        ]);
-
-        $this->connection->executeStreamingSql(Argument::allOf(
-            Argument::withEntry('sql', $sql),
-            Argument::withEntry('transaction', [
-                'id' => self::TRANSACTION,
-            ]),
-            Argument::withEntry('transactionOptions', [
-                'isolationLevel' => IsolationLevel::REPEATABLE_READ
-            ]),
-            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']])
-        ))->shouldBeCalled()->willReturn($this->resultGenerator(true));
 
         $this->refreshOperation($this->database, $this->connection->reveal());
+        $this->expectException(InvalidArgumentException::class);
+
         $res = $this->database->executePartitionedUpdate($sql, [
             'transactionOptions' => [
                 'isolationLevel' => IsolationLevel::REPEATABLE_READ

From 095b631d0b17ced8890dc3e8d27f9f76d41e0123 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Mon, 2 Jun 2025 21:41:17 +0000
Subject: [PATCH 08/24] Perform a transaction with the Client's isolation level
 when set

---
 Spanner/src/Database.php | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index ac096d0a9cfa..2b8d7305b27a 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -934,7 +934,9 @@ public function runTransaction(callable $operation, array $options = [])
         ];
 
         // There isn't anything configurable here.
-        $options['transactionOptions'] = $this->configureTransactionOptions($options['transactionOptions'] ?? []);
+        $options['transactionOptions'] = $this->configureTransactionOptions([
+            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
+        ]);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,

From 5823a912ce1d156f6a16364680a9f13f1dc87490 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 21:42:51 +0000
Subject: [PATCH 09/24] Pass the isolationLevel from the SpannerClient down to
 operation

---
 Spanner/src/Connection/Grpc.php |  2 ++
 Spanner/src/Database.php        | 16 ++++++++++++++--
 Spanner/src/Instance.php        | 11 ++++++++++-
 Spanner/src/SpannerClient.php   | 17 +++++++++++++++--
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/Spanner/src/Connection/Grpc.php b/Spanner/src/Connection/Grpc.php
index a70de619bf69..182f68fc23e7 100644
--- a/Spanner/src/Connection/Grpc.php
+++ b/Spanner/src/Connection/Grpc.php
@@ -1111,6 +1111,8 @@ public function beginTransaction(array $args)
             $pdml = new PartitionedDml();
             $options->setPartitionedDml($pdml);
             $args = $this->addLarHeader($args, $this->larEnabled);
+        } elseif (isset($transactionOptions['isolationLevel'])) {
+            $options->setIsolationLevel($transactionOptions['isolationLevel']);
         }
 
         // NOTE: if set for read-only actions, will throw exception
diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 583a5e9c2aee..257b1ccfafec 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -37,6 +37,7 @@
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
 
@@ -192,6 +193,11 @@ class Database
      */
     private $returnInt64AsObject;
 
+    /**
+     * @var int
+     */
+    private int $isolationLevel;
+
     /**
      * Create an object representing a Database.
      *
@@ -210,6 +216,8 @@ class Database
      *        be returned as a {@see \Google\Cloud\Core\Int64} object for 32 bit
      *        platform compatibility. **Defaults to** false.
      * @param string $databaseRole The user created database role which creates the session.
+     * @param int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      */
     public function __construct(
         ConnectionInterface $connection,
@@ -221,7 +229,8 @@ public function __construct(
         ?SessionPoolInterface $sessionPool = null,
         $returnInt64AsObject = false,
         array $info = [],
-        $databaseRole = ''
+        $databaseRole = '',
+        $isolationLevel = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
     ) {
         $this->connection = $connection;
         $this->instance = $instance;
@@ -239,6 +248,7 @@ public function __construct(
         $this->databaseRole = $databaseRole;
         $this->directedReadOptions = $instance->directedReadOptions();
         $this->returnInt64AsObject = $returnInt64AsObject;
+        $this->isolationLevel = $isolationLevel;
     }
 
     /**
@@ -813,7 +823,9 @@ public function transaction(array $options = [])
         }
 
         // There isn't anything configurable here.
-        $options['transactionOptions'] = $this->configureTransactionOptions();
+        $options['transactionOptions'] = $this->configureTransactionOptions([
+            'isolationLevel' => $this->isolationLevel
+        ]);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,
diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index b8fa34e9f4cf..43accfdf10e9 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -126,6 +126,11 @@ class Instance
      */
     private $directedReadOptions;
 
+    /**
+     * @var int
+     */
+    private $isolationLevel;
+
     /**
      * Create an object representing a Cloud Spanner instance.
      *
@@ -148,6 +153,8 @@ class Instance
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions}
      *           If using the `replicaSelection::type` setting, utilize the constants available in
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions\ReplicaSelection\Type} to set a value.
+     * @param int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      */
     public function __construct(
@@ -168,6 +175,7 @@ public function __construct(
 
         $this->setLroProperties($lroConnection, $lroCallables, $this->name);
         $this->directedReadOptions = $options['directedReadOptions'] ?? [];
+        $this->isolationLevel = $options['isolationLevel'];
     }
 
     /**
@@ -530,7 +538,8 @@ public function database($name, array $options = [])
             isset($options['sessionPool']) ? $options['sessionPool'] : null,
             $this->returnInt64AsObject,
             isset($options['database']) ? $options['database'] : [],
-            isset($options['databaseRole']) ? $options['databaseRole'] : ''
+            isset($options['databaseRole']) ? $options['databaseRole'] : '',
+            isset($options['isolationLevel']) ? $options['isolationLevel'] : $this->isolationLevel,
         );
     }
 
diff --git a/Spanner/src/SpannerClient.php b/Spanner/src/SpannerClient.php
index 64a969177cde..42d39c14d0e6 100644
--- a/Spanner/src/SpannerClient.php
+++ b/Spanner/src/SpannerClient.php
@@ -36,6 +36,7 @@
 use Google\Cloud\Spanner\Connection\LongRunningConnection;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Psr\Cache\CacheItemPoolInterface;
 use Psr\Http\StreamInterface;
 
@@ -138,6 +139,11 @@ class SpannerClient
      */
     private $directedReadOptions;
 
+    /**
+     * @var int
+     */
+    private $isolationLevel;
+
     /**
      * Create a Spanner client. Please note that this client requires
      * [the gRPC extension](https://cloud.google.com/php/grpc).
@@ -201,6 +207,8 @@ class SpannerClient
      *           **Defaults to** `true` (enabled).
      *     @type string $universeDomain The expected universe of the credentials. Defaults to
      *            "googleapis.com"
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @throws GoogleException If the gRPC extension is not enabled.
      */
@@ -218,7 +226,8 @@ public function __construct(array $config = [])
             'projectIdRequired' => true,
             'hasEmulator' => (bool) $emulatorHost,
             'emulatorHost' => $emulatorHost,
-            'queryOptions' => []
+            'queryOptions' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED,
         ];
 
         if (!empty($config['useDiscreteBackoffs'])) {
@@ -279,6 +288,7 @@ public function __construct(array $config = [])
         ]);
 
         $this->directedReadOptions = $config['directedReadOptions'] ?? [];
+        $this->isolationLevel = $config['isolationLevel'];
     }
 
     /**
@@ -558,7 +568,10 @@ public function instance($name, array $instance = [])
             $name,
             $this->returnInt64AsObject,
             $instance,
-            ['directedReadOptions' => $this->directedReadOptions]
+            [
+                'directedReadOptions' => $this->directedReadOptions,
+                'isolationLevel' => $this->isolationLevel
+            ]
         );
     }
 

From 76f0512ff31129c8bdcc2a91be004cef93fa120c Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 23:24:24 +0000
Subject: [PATCH 10/24] Add support for isolationLevel to the Database class

---
 Spanner/src/Connection/Grpc.php               | 4 +++-
 Spanner/src/Database.php                      | 9 +++++++--
 Spanner/src/Operation.php                     | 6 +++++-
 Spanner/src/Transaction.php                   | 2 ++
 Spanner/src/TransactionConfigurationTrait.php | 4 ++++
 5 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Spanner/src/Connection/Grpc.php b/Spanner/src/Connection/Grpc.php
index 182f68fc23e7..a5395dca5201 100644
--- a/Spanner/src/Connection/Grpc.php
+++ b/Spanner/src/Connection/Grpc.php
@@ -1111,7 +1111,9 @@ public function beginTransaction(array $args)
             $pdml = new PartitionedDml();
             $options->setPartitionedDml($pdml);
             $args = $this->addLarHeader($args, $this->larEnabled);
-        } elseif (isset($transactionOptions['isolationLevel'])) {
+        }
+
+        if (isset($transactionOptions['isolationLevel'])) {
             $options->setIsolationLevel($transactionOptions['isolationLevel']);
         }
 
diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 257b1ccfafec..b339ed190626 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -811,6 +811,8 @@ public function snapshot(array $options = [])
      *           Session labels may be applied using the `labels` key.
      *     @type string $tag A transaction tag. Requests made using this transaction will
      *           use this as the transaction tag.
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @return Transaction
      * @throws \BadMethodCallException If attempting to call this method within
@@ -822,9 +824,8 @@ public function transaction(array $options = [])
             throw new \BadMethodCallException('Nested transactions are not supported by this client.');
         }
 
-        // There isn't anything configurable here.
         $options['transactionOptions'] = $this->configureTransactionOptions([
-            'isolationLevel' => $this->isolationLevel
+            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
         ]);
 
         $session = $this->selectSession(
@@ -949,6 +950,10 @@ public function runTransaction(callable $operation, array $options = [])
                 if (!isset($options['transactionOptions']['partitionedDml'])) {
                     $options['begin'] = $options['transactionOptions'];
                 }
+
+                if (!isset($options['transactionOptions']['isolationLevel'])) {
+                    $options['transactionOptions']['isolationLevel'] = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
+                }
             } else {
                 $options['isRetry'] = true;
             }
diff --git a/Spanner/src/Operation.php b/Spanner/src/Operation.php
index 6c8aeecace91..e9f4d9748994 100644
--- a/Spanner/src/Operation.php
+++ b/Spanner/src/Operation.php
@@ -25,6 +25,7 @@
 use Google\Cloud\Spanner\Connection\ConnectionInterface;
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Rpc\Code;
 use InvalidArgumentException;
 
@@ -455,6 +456,8 @@ public function read(
      *           `false`.
      *     @type array $begin The begin transaction options.
      *           [Refer](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#transactionoptions)
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @return Transaction
      */
@@ -463,7 +466,8 @@ public function transaction(Session $session, array $options = [])
         $options += [
             'singleUse' => false,
             'isRetry' => false,
-            'requestOptions' => []
+            'requestOptions' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
         ];
         $transactionTag = $this->pluck('tag', $options, false);
         if (isset($transactionTag)) {
diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index 3d740cac45f3..b7a1577e5777 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -98,6 +98,8 @@ class Transaction implements TransactionalReadInterface
      *
      *     @type array $begin The begin Transaction options.
      *           [Refer](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#transactionoptions)
+     *     @type int $isolationLevel level of Isolation for this transaction instance
+     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @param ValueMapper $mapper Consumed internally for properly map mutation data.
      * @throws \InvalidArgumentException if a tag is specified on a single-use transaction.
diff --git a/Spanner/src/TransactionConfigurationTrait.php b/Spanner/src/TransactionConfigurationTrait.php
index 31dfa76809c7..f0b6219174bf 100644
--- a/Spanner/src/TransactionConfigurationTrait.php
+++ b/Spanner/src/TransactionConfigurationTrait.php
@@ -152,6 +152,10 @@ private function configureTransactionOptions(array $options = [])
             $transactionOptions['excludeTxnFromChangeStreams'] = $options['excludeTxnFromChangeStreams'];
         }
 
+        if (isset($options['isolationLevel'])) {
+            $transactionOptions['isolationLevel'] = $options['isolationLevel'];
+        }
+
         return $transactionOptions;
     }
 

From 1185ae4ba48054ad2affa7e57f0d90ebd0646bed Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 15 Apr 2025 23:26:15 +0000
Subject: [PATCH 11/24] Update the Instance class

---
 Spanner/src/Instance.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index 43accfdf10e9..97fa56920444 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -539,7 +539,7 @@ public function database($name, array $options = [])
             $this->returnInt64AsObject,
             isset($options['database']) ? $options['database'] : [],
             isset($options['databaseRole']) ? $options['databaseRole'] : '',
-            isset($options['isolationLevel']) ? $options['isolationLevel'] : $this->isolationLevel,
+            $options['isolationLevel'] ?? $this->isolationLevel,
         );
     }
 

From e8d54c738ceb849eeee40326fd01bed701a693cf Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 16 Apr 2025 21:40:43 +0000
Subject: [PATCH 12/24] Add configuration for Database

---
 Spanner/src/Database.php    | 21 +++++++++++++++++----
 Spanner/src/Instance.php    |  3 ++-
 Spanner/src/Transaction.php | 12 ++++++++++++
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index b339ed190626..ee9f687c0286 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -1648,11 +1648,12 @@ public function delete($table, KeySet $keySet, array $options = [])
      *           timestamp.
      *     @type Duration $exactStaleness Represents a number of seconds. Executes
      *           all reads at a timestamp that is $exactStaleness old.
-     *     @type bool $begin If true, will begin a new transaction. If a
+     *     @type bool|array $begin If true, will begin a new transaction. If a
      *           read/write transaction is desired, set the value of
      *           $transactionType. If a transaction or snapshot is created, it
      *           will be returned as `$result->transaction()` or
      *           `$result->snapshot()`. **Defaults to** `false`.
+     *           If $begin is an array {@see TransactionOptions}
      *     @type string $transactionType One of `SessionPoolInterface::CONTEXT_READ`
      *           or `SessionPoolInterface::CONTEXT_READWRITE`. If read/write is
      *           chosen, any snapshot options will be disregarded. If `$begin`
@@ -1697,12 +1698,16 @@ public function execute($sql, array $options = [])
                 $this->pluck('sessionOptions', $options, false) ?: []
             );
 
-        list(
+        [
             $options['transaction'],
             $options['transactionContext']
-        ) = $this->transactionSelector($options);
+        ] = $this->transactionSelector($options);
         $options = $this->addLarHeader($options, true, $options['transactionContext']);
 
+        if ($options['transactionType'] === SessionPoolInterface::CONTEXT_READWRITE && $this->isolationLevel) {
+            $options['transaction']['begin']['isolationLevel'] ??= $this->isolationLevel;
+        }
+
         $options['directedReadOptions'] = $this->configureDirectedReadOptions(
             $options,
             $this->directedReadOptions ?? []
@@ -1767,7 +1772,7 @@ public function mutationGroup()
      *           transactions.
      * }
      *
-     * @retur \Generator {@see \Google\Cloud\Spanner\V1\BatchWriteResponse}
+     * @return \Generator {@see \Google\Cloud\Spanner\V1\BatchWriteResponse}
      *
      * @throws ApiException if the remote call fails
      */
@@ -1911,6 +1916,8 @@ public function batchWrite(array $mutationGroups, array $options = [])
      *           Please note, if using the `priority` setting you may utilize the constants available
      *           on {@see \Google\Cloud\Spanner\V1\RequestOptions\Priority} to set a value.
      *           Please note, the `transactionTag` setting will be ignored as it is not supported for partitioned DML.
+     *     @type array $transactionOptions Transaction options.
+     *           {@see V1\TransactionOptions}
      * }
      * @return int The number of rows modified.
      */
@@ -1924,10 +1931,16 @@ public function executePartitionedUpdate($statement, array $options = [])
                 'partitionedDml' => [],
             ]
         ];
+
         if (isset($options['transactionOptions']['excludeTxnFromChangeStreams'])) {
             $beginTransactionOptions['transactionOptions']['excludeTxnFromChangeStreams'] =
                 $options['transactionOptions']['excludeTxnFromChangeStreams'];
         }
+
+        if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
+            $options['transactionOptions']['isolationLevel'] ??= $this->isolationLevel;
+        }
+
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
 
         $options = $this->addLarHeader($options);
diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index 97fa56920444..80fdd9a53177 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -32,6 +32,7 @@
 use Google\Cloud\Spanner\Connection\ConnectionInterface;
 use Google\Cloud\Spanner\Connection\IamInstance;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * Represents a Cloud Spanner instance
@@ -175,7 +176,7 @@ public function __construct(
 
         $this->setLroProperties($lroConnection, $lroCallables, $this->name);
         $this->directedReadOptions = $options['directedReadOptions'] ?? [];
-        $this->isolationLevel = $options['isolationLevel'];
+        $this->isolationLevel = $options['isolationLevel'] ?? IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
     }
 
     /**
diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index b7a1577e5777..6af89ce71f48 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -248,6 +248,18 @@ public function executeUpdate($sql, array $options = [])
                 . ' This option should be set at the transaction level.'
             );
         }
+
+        if (
+            $this->type() === self::TYPE_SINGLE_USE &&
+            isset($options['transaction']['begin']['isolationLevel']) ||
+            isset($options['transaction']['single_use']['isolationLevel'])
+        ) {
+            throw new ValidationException(
+                'The isolation level can only be applied to read/write transactions.'.
+                'Single use transactions are not read/write',
+            );
+        }
+
         $options = $this->buildUpdateOptions($options);
         return $this->operation
             ->executeUpdate($this->session, $this, $sql, $options);

From 06896015e6d3c49c6614b28559562dfe0f7d9d56 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 20:27:41 +0000
Subject: [PATCH 13/24] Add tests for isolationLevel

---
 Spanner/src/Database.php                   |   9 +-
 Spanner/tests/System/TransactionTest.php   |   6 +
 Spanner/tests/Unit/DatabaseTest.php        | 140 +++++++++++++++++++++
 Spanner/tests/Unit/TransactionTypeTest.php |  10 +-
 4 files changed, 158 insertions(+), 7 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index ee9f687c0286..5339168ffa6f 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -1698,13 +1698,13 @@ public function execute($sql, array $options = [])
                 $this->pluck('sessionOptions', $options, false) ?: []
             );
 
-        [
+        list(
             $options['transaction'],
             $options['transactionContext']
-        ] = $this->transactionSelector($options);
+        ) = $this->transactionSelector($options);
         $options = $this->addLarHeader($options, true, $options['transactionContext']);
 
-        if ($options['transactionType'] === SessionPoolInterface::CONTEXT_READWRITE && $this->isolationLevel) {
+        if (isset($options['transaction']['readWrite'])) {
             $options['transaction']['begin']['isolationLevel'] ??= $this->isolationLevel;
         }
 
@@ -1938,7 +1938,8 @@ public function executePartitionedUpdate($statement, array $options = [])
         }
 
         if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
-            $options['transactionOptions']['isolationLevel'] ??= $this->isolationLevel;
+            $beginTransactionOptions['transactionOptions']['isolationLevel'] =
+                $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel;
         }
 
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
diff --git a/Spanner/tests/System/TransactionTest.php b/Spanner/tests/System/TransactionTest.php
index 99b9931cb025..02f3558f2185 100644
--- a/Spanner/tests/System/TransactionTest.php
+++ b/Spanner/tests/System/TransactionTest.php
@@ -22,6 +22,7 @@
 use Google\Cloud\Core\Exception\ServiceException;
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\V1\DirectedReadOptions\ReplicaSelection\Type as ReplicaType;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * @group spanner
@@ -409,6 +410,11 @@ public function testRunTransactionILBWithMultipleOperations()
                         'id' => $id,
                         'name' => uniqid(self::TESTING_PREFIX),
                         'birthday' => new Date(new \DateTime)
+                    ],
+                    'transaction' => [
+                        'begin' => [
+                            'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+                        ]
                     ]
                 ]
             );
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index a63c361fc6a8..78b37d67c0f6 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -57,6 +57,7 @@
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
 use Google\Cloud\Core\Exception\ServiceException;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 
 /**
  * @group spanner
@@ -970,6 +971,38 @@ public function testTransaction()
         $this->assertInstanceOf(Transaction::class, $t);
     }
 
+    public function testTransactionWithIsolationLevel()
+    {
+        $this->connection->beginTransaction(Argument::allOf(
+            Argument::withEntry('session', $this->session->name()),
+            Argument::withEntry(
+                'database',
+                DatabaseAdminClient::databaseName(
+                    self::PROJECT,
+                    self::INSTANCE,
+                    self::DATABASE
+                )
+            ),
+            Argument::withEntry('requestOptions', [
+                'transactionTag' => self::TRANSACTION_TAG,
+            ]),
+            Argument::withEntry('transactionOptions', [
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+            ])
+        ))
+            ->shouldBeCalled()
+            ->willReturn(['id' => self::TRANSACTION]);
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+
+        $t = $this->database->transaction([
+            'tag' => self::TRANSACTION_TAG,
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ]);
+        $this->assertInstanceOf(Transaction::class, $t);
+    }
+
     public function testTransactionNestedTransaction()
     {
         $this->expectException(\BadMethodCallException::class);
@@ -1258,6 +1291,34 @@ public function testExecute()
         $this->assertEquals(10, $rows[0]['ID']);
     }
 
+    public function testExecuteWithIsolationLevel()
+    {
+        $sql = 'SELECT * FROM Table';
+
+        $this->connection->executeStreamingSql(Argument::allOf(
+            Argument::withEntry('sql', $sql),
+            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']]),
+            Argument::withEntry('transaction', [
+                'begin' => [
+                    'readWrite' => [],
+                    'isolationLevel' => IsolationLevel::REPEATABLE_READ
+                ]
+            ])
+        ))->shouldBeCalled()->willReturn($this->resultGenerator());
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+
+        $res = $this->database->execute($sql, [
+            'transactionType' => SessionPoolInterface::CONTEXT_READWRITE,
+            'begin' => [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]
+        ]);
+        $this->assertInstanceOf(Result::class, $res);
+        $rows = iterator_to_array($res->rows());
+        $this->assertEquals(10, $rows[0]['ID']);
+    }
+
     public function testExecuteWithSingleSession()
     {
         $this->database->___setProperty('sessionPool', null);
@@ -1332,6 +1393,40 @@ public function testExecutePartitionedUpdate()
         $this->assertEquals(1, $res);
     }
 
+    public function testExecutePartitionedUpdateWithIsolationLevel()
+    {
+        $sql = 'UPDATE foo SET bar = @bar';
+        $this->connection->beginTransaction(Argument::allOf(
+            Argument::withEntry('transactionOptions', [
+                'partitionedDml' => [],
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+            ]),
+            Argument::withEntry('singleUse', false)
+        ))->shouldBeCalled()->willReturn([
+            'id' => self::TRANSACTION
+        ]);
+
+        $this->connection->executeStreamingSql(Argument::allOf(
+            Argument::withEntry('sql', $sql),
+            Argument::withEntry('transaction', [
+                'id' => self::TRANSACTION,
+            ]),
+            Argument::withEntry('transactionOptions', [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]),
+            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']])
+        ))->shouldBeCalled()->willReturn($this->resultGenerator(true));
+
+        $this->refreshOperation($this->database, $this->connection->reveal());
+        $res = $this->database->executePartitionedUpdate($sql, [
+            'transactionOptions' => [
+                'isolationLevel' => IsolationLevel::REPEATABLE_READ
+            ]
+        ]);
+
+        $this->assertEquals(1, $res);
+    }
+
     public function testRead()
     {
         $table = 'Table';
@@ -2139,6 +2234,51 @@ public function testBatchWriteWithExcludeTxnFromChangeStreams()
         ]);
     }
 
+    public function testRunTransactionIsolationLevel()
+    {
+        $gapic = $this->prophesize(SpannerClient::class);
+
+        $sessName = SpannerClient::sessionName(self::PROJECT, self::INSTANCE, self::DATABASE, self::SESSION);
+        $session = new SessionProto(['name' => $sessName]);
+        $resultSet = new ResultSet(['stats' => new ResultSetStats(['row_count_exact' => 0])]);
+        $gapic->createSession(Argument::cetera())->shouldBeCalled()->willReturn($session);
+        $gapic->deleteSession(Argument::cetera())->shouldBeCalled();
+
+        $sql = 'SELECT example FROM sql_query';
+        $stream = $this->prophesize(ServerStream::class);
+        $stream->readAll()->shouldBeCalledOnce()->willReturn([$resultSet]);
+        $gapic->executeStreamingSql($sessName, $sql, Argument::that(function (array $options) {
+            $this->assertArrayHasKey('transaction', $options);
+            $this->assertNotNull($transactionOptions = $options['transaction']->getBegin());
+            $this->assertEquals(IsolationLevel::REPEATABLE_READ, $transactionOptions->getIsolationLevel());
+            return true;
+        }))
+            ->shouldBeCalledOnce()
+            ->willReturn($stream->reveal());
+
+        $database = new Database(
+            new Grpc(['gapicSpannerClient' => $gapic->reveal()]),
+            $this->instance,
+            $this->lro->reveal(),
+            $this->lroCallables,
+            self::PROJECT,
+            self::DATABASE
+        );
+
+        $database->runTransaction(
+            function (Transaction $t) use ($sql) {
+                // Run a fake query
+                $t->executeUpdate($sql);
+
+                // Simulate calling Transaction::commmit()
+                $prop = new \ReflectionProperty($t, 'state');
+                $prop->setAccessible(true);
+                $prop->setValue($t, Transaction::STATE_COMMITTED);
+            },
+            ['transactionOptions' => ['isolationLevel' => IsolationLevel::REPEATABLE_READ]]
+        );
+    }
+
     private function createStreamingAPIArgs()
     {
         $row = ['id' => 1];
diff --git a/Spanner/tests/Unit/TransactionTypeTest.php b/Spanner/tests/Unit/TransactionTypeTest.php
index d228794c863b..210d07a04d73 100644
--- a/Spanner/tests/Unit/TransactionTypeTest.php
+++ b/Spanner/tests/Unit/TransactionTypeTest.php
@@ -34,6 +34,7 @@
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\Transaction;
 use Google\Cloud\Spanner\V1\SpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
@@ -84,7 +85,8 @@ public function testDatabaseRunTransactionPreAllocate()
         $this->connection->beginTransaction(Argument::allOf(
             Argument::withEntry('singleUse', false),
             Argument::withEntry('transactionOptions', [
-                'readWrite' => []
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
             ])
         ))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
@@ -123,7 +125,8 @@ public function testDatabaseTransactionPreAllocate()
         $this->connection->beginTransaction(Argument::allOf(
             Argument::withEntry('singleUse', false),
             Argument::withEntry('transactionOptions', [
-                'readWrite' => []
+                'readWrite' => [],
+                'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED,
             ])
         ))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
@@ -740,7 +743,8 @@ public function testDatabaseReadBeginReadWrite($chunks)
     public function testTransactionPreAllocatedRollback()
     {
         $this->connection->beginTransaction(Argument::withEntry('transactionOptions', [
-            'readWrite' => []
+            'readWrite' => [],
+            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
         ]))->shouldBeCalledTimes(1)->willReturn(['id' => self::TRANSACTION]);
 
         $sess = SpannerClient::sessionName(

From 80625cd450f8fa5a075820e704490c2adfb3c822 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 20:34:55 +0000
Subject: [PATCH 14/24] Fix style issues

---
 Spanner/src/Transaction.php | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index 6af89ce71f48..dd7d3d76d4a0 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -249,13 +249,12 @@ public function executeUpdate($sql, array $options = [])
             );
         }
 
-        if (
-            $this->type() === self::TYPE_SINGLE_USE &&
+        if ($this->type() === self::TYPE_SINGLE_USE &&
             isset($options['transaction']['begin']['isolationLevel']) ||
             isset($options['transaction']['single_use']['isolationLevel'])
         ) {
             throw new ValidationException(
-                'The isolation level can only be applied to read/write transactions.'.
+                'The isolation level can only be applied to read/write transactions.' .
                 'Single use transactions are not read/write',
             );
         }

From fac546098cd985c41a6b03aaa3bff211a8b5abeb Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Thu, 17 Apr 2025 21:47:19 +0000
Subject: [PATCH 15/24] Update the executePartitionUpdate method

---
 Spanner/src/Database.php            | 11 ++++++-----
 Spanner/tests/Unit/DatabaseTest.php | 26 +++++---------------------
 2 files changed, 11 insertions(+), 26 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 5339168ffa6f..c895e7e9e9aa 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -40,6 +40,7 @@
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
+use InvalidArgumentException;
 
 /**
  * Represents a Cloud Spanner Database.
@@ -1924,6 +1925,11 @@ public function batchWrite(array $mutationGroups, array $options = [])
     public function executePartitionedUpdate($statement, array $options = [])
     {
         unset($options['requestOptions']['transactionTag']);
+
+        if (isset($options['transactionOptions']['isolationLevel'])) {
+            throw new InvalidArgumentException('Partitioned DML cannot be configured with an isolation level');
+        }
+
         $session = $this->selectSession(SessionPoolInterface::CONTEXT_READWRITE);
 
         $beginTransactionOptions = [
@@ -1937,11 +1943,6 @@ public function executePartitionedUpdate($statement, array $options = [])
                 $options['transactionOptions']['excludeTxnFromChangeStreams'];
         }
 
-        if (isset($options['transactionOptions']['isolationLevel']) || $this->isolationLevel) {
-            $beginTransactionOptions['transactionOptions']['isolationLevel'] =
-                $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel;
-        }
-
         $transaction = $this->operation->transaction($session, $beginTransactionOptions);
 
         $options = $this->addLarHeader($options);
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index 78b37d67c0f6..dabbb3a4758b 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -58,6 +58,8 @@
 use Prophecy\PhpUnit\ProphecyTrait;
 use Google\Cloud\Core\Exception\ServiceException;
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
+use InvalidArgumentException;
+use Kreait\Firebase\Exception\Messaging\InvalidArgument;
 
 /**
  * @group spanner
@@ -1393,31 +1395,13 @@ public function testExecutePartitionedUpdate()
         $this->assertEquals(1, $res);
     }
 
-    public function testExecutePartitionedUpdateWithIsolationLevel()
+    public function testExecutePartitionedUpdateWithIsolationLevelShouldRaise()
     {
         $sql = 'UPDATE foo SET bar = @bar';
-        $this->connection->beginTransaction(Argument::allOf(
-            Argument::withEntry('transactionOptions', [
-                'partitionedDml' => [],
-                'isolationLevel' => IsolationLevel::REPEATABLE_READ,
-            ]),
-            Argument::withEntry('singleUse', false)
-        ))->shouldBeCalled()->willReturn([
-            'id' => self::TRANSACTION
-        ]);
-
-        $this->connection->executeStreamingSql(Argument::allOf(
-            Argument::withEntry('sql', $sql),
-            Argument::withEntry('transaction', [
-                'id' => self::TRANSACTION,
-            ]),
-            Argument::withEntry('transactionOptions', [
-                'isolationLevel' => IsolationLevel::REPEATABLE_READ
-            ]),
-            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']])
-        ))->shouldBeCalled()->willReturn($this->resultGenerator(true));
 
         $this->refreshOperation($this->database, $this->connection->reveal());
+        $this->expectException(InvalidArgumentException::class);
+
         $res = $this->database->executePartitionedUpdate($sql, [
             'transactionOptions' => [
                 'isolationLevel' => IsolationLevel::REPEATABLE_READ

From 9750d98723a2ad44858b8023fde3466c800d300f Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Mon, 2 Jun 2025 21:41:17 +0000
Subject: [PATCH 16/24] Perform a transaction with the Client's isolation level
 when set

---
 Spanner/src/Database.php | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index c895e7e9e9aa..a2cde3ffd347 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -935,7 +935,9 @@ public function runTransaction(callable $operation, array $options = [])
         ];
 
         // There isn't anything configurable here.
-        $options['transactionOptions'] = $this->configureTransactionOptions($options['transactionOptions'] ?? []);
+        $options['transactionOptions'] = $this->configureTransactionOptions([
+            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
+        ]);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,

From 2a230cd9bf21e9dd3701d47cd073d2a0bce0b1da Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 4 Jun 2025 17:45:12 +0000
Subject: [PATCH 17/24] Fix test issues

---
 Spanner/src/Database.php            | 11 ++++++++---
 Spanner/src/Operation.php           |  2 +-
 Spanner/tests/Unit/DatabaseTest.php |  2 +-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index a2cde3ffd347..e4271944d460 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -37,6 +37,7 @@
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\Session\SessionPoolInterface;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
+use Google\Cloud\Spanner\V1\TransactionOptions;
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
@@ -918,6 +919,8 @@ public function transaction(array $options = [])
      *           Session labels may be applied using the `labels` key.
      *     @type string $tag A transaction tag. Requests made using this transaction will
      *           use this as the transaction tag.
+     *     @type array transactionOptions Options for the transaction. {@see \Google\Cloud\Spanner\V1\TransactionOptions}
+     *           for available options
      * }
      * @return mixed The return value of `$operation`.
      * @throws \RuntimeException If a transaction is not committed or rolled back.
@@ -934,10 +937,12 @@ public function runTransaction(callable $operation, array $options = [])
             'maxRetries' => self::MAX_RETRIES,
         ];
 
+        if (!isset($options['transactionOptions']['isolationLevel'])) {
+            $options['transactionOptions']['isolationLevel'] = $this->isolationLevel;
+        }
+
         // There isn't anything configurable here.
-        $options['transactionOptions'] = $this->configureTransactionOptions([
-            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
-        ]);
+        $options['transactionOptions'] = $this->configureTransactionOptions($options['transactionOptions'] ?? []);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,
diff --git a/Spanner/src/Operation.php b/Spanner/src/Operation.php
index e9f4d9748994..5cddb1749911 100644
--- a/Spanner/src/Operation.php
+++ b/Spanner/src/Operation.php
@@ -467,7 +467,7 @@ public function transaction(Session $session, array $options = [])
             'singleUse' => false,
             'isRetry' => false,
             'requestOptions' => [],
-            'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
+            // 'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
         ];
         $transactionTag = $this->pluck('tag', $options, false);
         if (isset($transactionTag)) {
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index dabbb3a4758b..973ead97d3ec 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -82,7 +82,7 @@ class DatabaseTest extends TestCase
     const TRANSACTION_TAG = 'my-transaction-tag';
     const TEST_TABLE_NAME = 'Users';
     const TIMESTAMP = '2017-01-09T18:05:22.534799Z';
-    const BEGIN_RW_OPTIONS = ['begin' => ['readWrite' => []]];
+    const BEGIN_RW_OPTIONS = ['begin' => ['readWrite' => [], 'isolationLevel' => 0]];
 
     private $connection;
     private $instance;

From ffaecf519269cc3a803dbbe7eecc6684645eda7e Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 4 Jun 2025 18:31:22 +0000
Subject: [PATCH 18/24] Change logic for assinging IsolationLevel on
 runTransaction

---
 Spanner/src/Database.php  | 17 +++++++++--------
 Spanner/src/Operation.php |  4 +---
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index 37bc7d7eb22a..f38dd8e80251 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -937,14 +937,15 @@ public function runTransaction(callable $operation, array $options = [])
             'maxRetries' => self::MAX_RETRIES,
         ];
 
-        if (!isset($options['transactionOptions']['isolationLevel'])) {
+        $transactionOptions = (isset($options['transactionOptions'])) ? $options['transactionOptions'] : [];
+
+        if (!isset($transactionOptions['isolationLevel'])) {
             $options['transactionOptions']['isolationLevel'] = $this->isolationLevel;
         }
 
-        // There isn't anything configurable here.
         $options['transactionOptions'] = $this->configureTransactionOptions([
-            'isolationLevel' => $options['isolationLevel'] ?? $this->isolationLevel
-        ]);
+            'isolationLevel' => $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel
+        ] + $transactionOptions);
 
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,
@@ -956,14 +957,14 @@ public function runTransaction(callable $operation, array $options = [])
 
             // Initial attempt requires to set `begin` options (ILB).
             if ($attempt === 0) {
+                if (!isset($options['transactionOptions']['isolationLevel'])) {
+                    $options['transactionOptions']['isolationLevel'] = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
+                }
+
                 // Partitioned DML does not support ILB.
                 if (!isset($options['transactionOptions']['partitionedDml'])) {
                     $options['begin'] = $options['transactionOptions'];
                 }
-
-                if (!isset($options['transactionOptions']['isolationLevel'])) {
-                    $options['transactionOptions']['isolationLevel'] = IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED;
-                }
             } else {
                 $options['isRetry'] = true;
             }
diff --git a/Spanner/src/Operation.php b/Spanner/src/Operation.php
index 5cddb1749911..b47e439ac4ce 100644
--- a/Spanner/src/Operation.php
+++ b/Spanner/src/Operation.php
@@ -457,7 +457,6 @@ public function read(
      *     @type array $begin The begin transaction options.
      *           [Refer](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#transactionoptions)
      *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
-     *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      * @return Transaction
      */
@@ -466,8 +465,7 @@ public function transaction(Session $session, array $options = [])
         $options += [
             'singleUse' => false,
             'isRetry' => false,
-            'requestOptions' => [],
-            // 'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
+            'requestOptions' => []
         ];
         $transactionTag = $this->pluck('tag', $options, false);
         if (isset($transactionTag)) {

From c24dbd5ed23a003182b0d82d45aa8b077e75eee8 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 4 Jun 2025 19:02:16 +0000
Subject: [PATCH 19/24] Fix the SnippetDatabase test

---
 Spanner/tests/Snippet/DatabaseTest.php | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Spanner/tests/Snippet/DatabaseTest.php b/Spanner/tests/Snippet/DatabaseTest.php
index 486efd3922e0..d6c4c15eda24 100644
--- a/Spanner/tests/Snippet/DatabaseTest.php
+++ b/Spanner/tests/Snippet/DatabaseTest.php
@@ -40,6 +40,7 @@
 use Google\Cloud\Spanner\Tests\StubCreationTrait;
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\Transaction;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
 
@@ -462,7 +463,7 @@ public function testRunTransactionRollback()
             ->shouldBeCalled();
 
         $this->connection->executeStreamingSql(
-            Argument::withEntry('transaction', ['begin' => ['readWrite' => []]])
+            Argument::withEntry('transaction', ['begin' => ['readWrite' => [], 'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED]])
         )
             ->shouldBeCalled()
             ->willReturn($this->resultGeneratorData([

From 1990b0380e6736997fc5beeff36d2b6f7103b4c0 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Wed, 4 Jun 2025 19:13:58 +0000
Subject: [PATCH 20/24] Fix styling issues

---
 Spanner/src/Database.php               | 3 ++-
 Spanner/src/Operation.php              | 1 -
 Spanner/tests/Snippet/DatabaseTest.php | 7 ++++++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index f38dd8e80251..5d2261322476 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -919,7 +919,8 @@ public function transaction(array $options = [])
      *           Session labels may be applied using the `labels` key.
      *     @type string $tag A transaction tag. Requests made using this transaction will
      *           use this as the transaction tag.
-     *     @type array transactionOptions Options for the transaction. {@see \Google\Cloud\Spanner\V1\TransactionOptions}
+     *     @type array transactionOptions Options for the transaction.
+     *           {@see \Google\Cloud\Spanner\V1\TransactionOptions}
      *           for available options
      * }
      * @return mixed The return value of `$operation`.
diff --git a/Spanner/src/Operation.php b/Spanner/src/Operation.php
index b47e439ac4ce..043d504bb6b5 100644
--- a/Spanner/src/Operation.php
+++ b/Spanner/src/Operation.php
@@ -25,7 +25,6 @@
 use Google\Cloud\Spanner\Connection\ConnectionInterface;
 use Google\Cloud\Spanner\Session\Session;
 use Google\Cloud\Spanner\V1\SpannerClient as GapicSpannerClient;
-use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Rpc\Code;
 use InvalidArgumentException;
 
diff --git a/Spanner/tests/Snippet/DatabaseTest.php b/Spanner/tests/Snippet/DatabaseTest.php
index d6c4c15eda24..0f0ab0493e0b 100644
--- a/Spanner/tests/Snippet/DatabaseTest.php
+++ b/Spanner/tests/Snippet/DatabaseTest.php
@@ -463,7 +463,12 @@ public function testRunTransactionRollback()
             ->shouldBeCalled();
 
         $this->connection->executeStreamingSql(
-            Argument::withEntry('transaction', ['begin' => ['readWrite' => [], 'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED]])
+            Argument::withEntry('transaction', [
+                'begin' => [
+                    'readWrite' => [],
+                    'isolationLevel' => IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
+                ]
+            ])
         )
             ->shouldBeCalled()
             ->willReturn($this->resultGeneratorData([

From 00e98f3c44f94863004261cfcbf23de987692463 Mon Sep 17 00:00:00 2001
From: Hector Mendoza Jacobo <hecmenjac@google.com>
Date: Fri, 3 Oct 2025 19:07:44 -0400
Subject: [PATCH 21/24] Add the correct documentation for snapshotIsolation

---
 Spanner/src/Database.php            | 3 ++-
 Spanner/src/Instance.php            | 4 +++-
 Spanner/src/Transaction.php         | 1 +
 Spanner/tests/Unit/DatabaseTest.php | 4 ++--
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index f6639fc77f46..cd971ee10bb6 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -1932,13 +1932,14 @@ public function batchWrite(array $mutationGroups, array $options = [])
      *           {@see V1\TransactionOptions}
      * }
      * @return int The number of rows modified.
+     * @throws ValidationException
      */
     public function executePartitionedUpdate($statement, array $options = [])
     {
         unset($options['requestOptions']['transactionTag']);
 
         if (isset($options['transactionOptions']['isolationLevel'])) {
-            throw new InvalidArgumentException('Partitioned DML cannot be configured with an isolation level');
+            throw new ValidationException('Partitioned DML cannot be configured with an isolation level');
         }
 
         $session = $this->selectSession(SessionPoolInterface::CONTEXT_READWRITE);
diff --git a/Spanner/src/Instance.php b/Spanner/src/Instance.php
index 80fdd9a53177..6ef646012a19 100644
--- a/Spanner/src/Instance.php
+++ b/Spanner/src/Instance.php
@@ -154,7 +154,7 @@ class Instance
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions}
      *           If using the `replicaSelection::type` setting, utilize the constants available in
      *           {@see \Google\Cloud\Spanner\V1\DirectedReadOptions\ReplicaSelection\Type} to set a value.
-     * @param int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
+     *     @type int $isolationLevel The level of Isolation for the transactions executed by this Client's instance.
      *           **Defaults to** IsolationLevel::ISOLATION_LEVEL_UNSPECIFIED
      * }
      */
@@ -524,6 +524,8 @@ public function createDatabaseFromBackup($name, $backup, array $options = [])
      *     @type SessionPoolInterface $sessionPool A pool used to manage
      *           sessions.
      *     @type string $databaseRole The user created database role which creates the session.
+     *     @type int $isolationLevel The IsolationLevel set for the transaction.
+     *           Check {@see IsolationLevel} for more details.
      * }
      * @return Database
      */
diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index dd7d3d76d4a0..9ad1dc750f49 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -239,6 +239,7 @@ public function getCommitStats()
      *         been set when creating the transaction.
      * }
      * @return int The number of rows modified.
+     * @throws ValidationException
      */
     public function executeUpdate($sql, array $options = [])
     {
diff --git a/Spanner/tests/Unit/DatabaseTest.php b/Spanner/tests/Unit/DatabaseTest.php
index 4d251ed07855..1157838fb0e2 100644
--- a/Spanner/tests/Unit/DatabaseTest.php
+++ b/Spanner/tests/Unit/DatabaseTest.php
@@ -18,6 +18,7 @@
 namespace Google\Cloud\Spanner\Tests\Unit;
 
 use Google\ApiCore\ServerStream;
+use Google\ApiCore\ValidationException;
 use Google\Cloud\Core\Exception\AbortedException;
 use Google\Cloud\Core\Exception\NotFoundException;
 use Google\Cloud\Core\Exception\ServerException;
@@ -59,7 +60,6 @@
 use Google\Cloud\Core\Exception\ServiceException;
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use InvalidArgumentException;
-use Kreait\Firebase\Exception\Messaging\InvalidArgument;
 use Google\Cloud\Spanner\V1\ReadRequest\LockHint;
 use Google\Cloud\Spanner\V1\ReadRequest\OrderBy;
 
@@ -1402,7 +1402,7 @@ public function testExecutePartitionedUpdateWithIsolationLevelShouldRaise()
         $sql = 'UPDATE foo SET bar = @bar';
 
         $this->refreshOperation($this->database, $this->connection->reveal());
-        $this->expectException(InvalidArgumentException::class);
+        $this->expectException(ValidationException::class);
 
         $res = $this->database->executePartitionedUpdate($sql, [
             'transactionOptions' => [

From 53892bcc47bbdf7d2bd289430693dbd56039ae00 Mon Sep 17 00:00:00 2001
From: Hector Mendoza Jacobo <hecmenjac@google.com>
Date: Fri, 3 Oct 2025 20:32:46 -0400
Subject: [PATCH 22/24] Remove unnecessary import

---
 Spanner/src/Database.php | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index b815bc76fa08..d712e99626fb 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -41,7 +41,6 @@
 use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use Google\Cloud\Spanner\V1\TypeCode;
 use Google\Rpc\Code;
-use InvalidArgumentException;
 
 /**
  * Represents a Cloud Spanner Database.

From 975ef470aa0dc813cd0324f1d48e623cbdc9624e Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 7 Oct 2025 01:40:10 +0000
Subject: [PATCH 23/24] Update logic for transaction to handle
 snapshotIsolation

---
 Spanner/src/Transaction.php              | 39 +++++++-----
 Spanner/tests/Unit/OperationTest.php     | 22 +++++++
 Spanner/tests/Unit/SpannerClientTest.php | 76 +++++++++++++++++++++++-
 Spanner/tests/Unit/TransactionTest.php   | 59 ++++++++++++++++++
 4 files changed, 181 insertions(+), 15 deletions(-)

diff --git a/Spanner/src/Transaction.php b/Spanner/src/Transaction.php
index 9ad1dc750f49..f72e554f3fb1 100644
--- a/Spanner/src/Transaction.php
+++ b/Spanner/src/Transaction.php
@@ -231,12 +231,15 @@ public function getCommitStats()
      *           parameter types. Likewise, for structs, use
      *           {@see \Google\Cloud\Spanner\StructType}.
      *     @type array $requestOptions Request options.
-     *         For more information on available options, please see
-     *         [the upstream documentation](https://cloud.google.com/spanner/docs/reference/rest/v1/RequestOptions).
-     *         Please note, if using the `priority` setting you may utilize the constants available
-     *         on {@see \Google\Cloud\Spanner\V1\RequestOptions\Priority} to set a value.
-     *         Please note, the `transactionTag` setting will be ignored as the transaction tag should have already
-     *         been set when creating the transaction.
+     *           For more information on available options, please see
+     *           [the upstream documentation](https://cloud.google.com/spanner/docs/reference/rest/v1/RequestOptions).
+     *           Please note, if using the `priority` setting you may utilize the constants available
+     *           on {@see \Google\Cloud\Spanner\V1\RequestOptions\Priority} to set a value.
+     *           Please note, the `transactionTag` setting will be ignored as the transaction tag should have already
+     *           been set when creating the transaction.
+     *     @type array $transaction a set of Options for a transaction selector.
+     *           For more details on these options please
+     *           {@see https://cloud.google.com/spanner/docs/reference/rest/v1/TransactionSelector}
      * }
      * @return int The number of rows modified.
      * @throws ValidationException
@@ -250,14 +253,17 @@ public function executeUpdate($sql, array $options = [])
             );
         }
 
-        if ($this->type() === self::TYPE_SINGLE_USE &&
-            isset($options['transaction']['begin']['isolationLevel']) ||
-            isset($options['transaction']['single_use']['isolationLevel'])
-        ) {
-            throw new ValidationException(
-                'The isolation level can only be applied to read/write transactions.' .
-                'Single use transactions are not read/write',
-            );
+        if (isset($options['transaction']['begin']['isolationLevel']) && empty($this->transactionId)) {
+            if (isset($options['transaction']['begin']['readOnly'])) {
+                // isolationLevel can only be used with read/write transactions
+                throw new ValidationException(
+                    'The isolation level can only be applied to read/write transactions.' .
+                    'Single use transactions are not read/write',
+                );
+            }
+
+            // We are planning to create a new transaction, switch to pre allocated.
+            $this->type = self::TYPE_PRE_ALLOCATED;
         }
 
         $options = $this->buildUpdateOptions($options);
@@ -530,6 +536,11 @@ public function isRetry()
     private function buildUpdateOptions(array $options): array
     {
         unset($options['requestOptions']['transactionTag']);
+
+        if (!empty($options['transaction']['begin'])) {
+            $options['begin'] = $this->pluck('transaction', $options)['begin'];
+        }
+
         if (isset($this->tag)) {
             $options['requestOptions']['transactionTag'] = $this->tag;
         }
diff --git a/Spanner/tests/Unit/OperationTest.php b/Spanner/tests/Unit/OperationTest.php
index 40a2c4c315ea..0f8a3def30c7 100644
--- a/Spanner/tests/Unit/OperationTest.php
+++ b/Spanner/tests/Unit/OperationTest.php
@@ -41,6 +41,7 @@
 use Google\Cloud\Spanner\V1\Transaction as TransactionProto;
 use Google\Cloud\Spanner\V1\TransactionOptions;
 use Google\Cloud\Spanner\V1\TransactionOptions\ReadWrite\ReadLockMode as ReadLockMode;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
@@ -343,6 +344,27 @@ public function testTransaction()
         $this->assertEquals(self::TRANSACTION, $t->id());
     }
 
+    public function testTransactioWithIsolationLevel()
+    {
+        $this->connection->beginTransaction(Argument::allOf(
+            Argument::withEntry('database', self::DATABASE),
+            Argument::withEntry('session', $this->session->name()),
+            Argument::withEntry('isolationLevel', IsolationLevel::REPEATABLE_READ)
+        ))
+            ->shouldBeCalled()
+            ->willReturn(['id' => self::TRANSACTION]);
+
+        $this->operation->___setProperty('connection', $this->connection->reveal());
+
+        $options = [
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ];
+
+        $t = $this->operation->transaction($this->session, $options);
+        $this->assertInstanceOf(Transaction::class, $t);
+        $this->assertEquals(self::TRANSACTION, $t->id());
+    }
+
     public function testTransactionNoTag()
     {
         $this->connection->beginTransaction(Argument::allOf(
diff --git a/Spanner/tests/Unit/SpannerClientTest.php b/Spanner/tests/Unit/SpannerClientTest.php
index beeb17033339..c3751f707ae0 100644
--- a/Spanner/tests/Unit/SpannerClientTest.php
+++ b/Spanner/tests/Unit/SpannerClientTest.php
@@ -41,10 +41,12 @@
 use Google\Cloud\Spanner\SpannerClient;
 use Google\Cloud\Spanner\Tests\StubCreationTrait;
 use Google\Cloud\Spanner\Timestamp;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
 use Prophecy\PhpUnit\ProphecyTrait;
+use ReflectionClass;
 
 /**
  * @group spanner
@@ -81,7 +83,7 @@ public function setUp(): void
         $this->client = TestHelpers::stub(SpannerClient::class, [
             [
                 'projectId' => self::PROJECT,
-                'directedReadOptions' => $this->directedReadOptionsIncludeReplicas
+                'directedReadOptions' => $this->directedReadOptionsIncludeReplicas,
             ]
         ]);
     }
@@ -473,4 +475,76 @@ public function testSpannerClientWithDirectedRead()
             $this->directedReadOptionsIncludeReplicas
         );
     }
+
+    public function testClientPassesIsolationLevel()
+    {
+        /** @var SpannerClient $client */
+        $client = new SpannerClient([
+            'projectId' => self::PROJECT,
+            'directedReadOptions' => $this->directedReadOptionsIncludeReplicas,
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ]);
+
+        $reflectedClient = new ReflectionClass($client);
+        $property = $reflectedClient->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($client)
+        );
+
+        $instance = $client->instance('test');
+        $reflectedInstance = new ReflectionClass($instance);
+        $property = $reflectedInstance->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($instance)
+        );
+
+        $database = $instance->database('test');
+        $reflectedDb = new ReflectionClass($database);
+        $property = $reflectedDb->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($database)
+        );
+    }
+
+    public function testTransactionHasCorrectIsolationLevel()
+    {
+        /** @var SpannerClient $client */
+        $client = new SpannerClient([
+            'projectId' => self::PROJECT,
+            'directedReadOptions' => $this->directedReadOptionsIncludeReplicas,
+            'isolationLevel' => IsolationLevel::REPEATABLE_READ
+        ]);
+
+        $reflectedClient = new ReflectionClass($client);
+        $property = $reflectedClient->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($client)
+        );
+
+        $instance = $client->instance('test');
+        $reflectedInstance = new ReflectionClass($instance);
+        $property = $reflectedInstance->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($instance)
+        );
+
+        $database = $instance->database('test');
+        $reflectedDb = new ReflectionClass($database);
+        $property = $reflectedDb->getProperty('isolationLevel');
+        $property->setAccessible(true);
+        $this->assertEquals(
+            IsolationLevel::REPEATABLE_READ,
+            $property->getValue($database)
+        );
+    }
 }
diff --git a/Spanner/tests/Unit/TransactionTest.php b/Spanner/tests/Unit/TransactionTest.php
index 1563a9c9c9b6..23e620889a31 100644
--- a/Spanner/tests/Unit/TransactionTest.php
+++ b/Spanner/tests/Unit/TransactionTest.php
@@ -33,6 +33,7 @@
 use Google\Cloud\Spanner\Tests\StubCreationTrait;
 use Google\Cloud\Spanner\Timestamp;
 use Google\Cloud\Spanner\Transaction;
+use Google\Cloud\Spanner\V1\TransactionOptions\IsolationLevel;
 use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
@@ -642,6 +643,64 @@ public function testIsRetryTrue()
         $this->assertTrue($transaction->isRetry());
     }
 
+    public function testExecuteUpdateWithIsolationLevel()
+    {
+        $sql = 'UPDATE foo SET bar = @bar';
+        $this->connection->executeStreamingSql(Argument::allOf(
+            Argument::withEntry('sql', $sql),
+            Argument::withEntry('transaction', [
+                'begin' => [
+                    'readWrite' => [],
+                    'isolationLevel' => IsolationLevel::REPEATABLE_READ
+                ]
+            ]),
+            Argument::withEntry('headers', ['x-goog-spanner-route-to-leader' => ['true']])
+        ))->shouldBeCalled()->willReturn($this->resultGenerator(true));
+
+        $this->refreshOperation($this->transaction, $this->connection->reveal());
+
+        // Transaction without an ID to be able to use `begin`
+        $transaction = new Transaction(
+            $this->operation,
+            $this->session
+        );
+
+        $options = [
+            'transaction' => [
+                'begin' => [
+                    'isolationLevel' => IsolationLevel::REPEATABLE_READ
+                ]
+            ]
+        ];
+
+        $res = $transaction->executeUpdate($sql, $options);
+
+        $this->assertEquals(1, $res);
+    }
+
+    public function testSingleUseWithIsolationLevelThrowsAnExceptionOnReadOnly()
+    {
+        $this->expectException(ValidationException::class);
+
+        $sql = 'UPDATE foo SET bar = @bar';
+
+        $this->refreshOperation($this->transaction, $this->connection->reveal());
+
+        $options = [
+            'transaction' => [
+                'begin' => [
+                    'isolationLevel' => IsolationLevel::REPEATABLE_READ,
+                    'readOnly' => []
+                ]
+            ]
+        ];
+
+        $res = $this->singleUseTransaction->executeUpdate($sql, $options);
+
+        $this->assertEquals(1, $res);
+    }
+
+
     // *******
     // Helpers
 

From a21c6a71cc81b3517dba034b603c6c69f13844a3 Mon Sep 17 00:00:00 2001
From: hectorhammett <hecmenjac@google.com>
Date: Tue, 7 Oct 2025 01:42:04 +0000
Subject: [PATCH 24/24] Removed unnecessary line

---
 Spanner/src/Database.php | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Spanner/src/Database.php b/Spanner/src/Database.php
index d712e99626fb..7772f54ab19b 100644
--- a/Spanner/src/Database.php
+++ b/Spanner/src/Database.php
@@ -940,8 +940,6 @@ public function runTransaction(callable $operation, array $options = [])
             'isolationLevel' => $options['transactionOptions']['isolationLevel'] ?? $this->isolationLevel
         ] + $transactionOptions);
 
-        $options['transactionOptions'] = $this->configureTransactionOptions($options['transactionOptions'] ?? []);
-
         $session = $this->selectSession(
             SessionPoolInterface::CONTEXT_READWRITE,
             $this->pluck('sessionOptions', $options, false) ?: []