Implement $not (#14)

See: https://www.mongodb.com/docs/manual/reference/operator/query/not/

---------

Co-authored-by: Koen Bollen <213502+koenbollen@users.noreply.github.com>

Author: erikdubbelboer

filter/converter.go

@@ -125,6 +125,20 @@ func (c *Converter) convertFilter(filter map[string]any, paramIndex int) (string
 					conditions = append(conditions, strings.Join(inner, " "+op+" "))
 				}
 			}
+		case "$not":
+			vv, ok := value.(map[string]any)
+			if !ok {
+				return "", nil, fmt.Errorf("invalid value for $not operator (must be object): %v", value)
+			}
+			innerConditions, innerValues, err := c.convertFilter(vv, paramIndex)
+			if err != nil {
+				return "", nil, err
+			}
+			paramIndex += len(innerValues)
+			// Just putting a NOT around the condition is not enough, a non existing jsonb field will for example
+			// make the whole inner condition NULL. And NOT NULL is still a falsy value, so we need to check for NULL explicitly.
+			conditions = append(conditions, fmt.Sprintf("(NOT COALESCE(%s, FALSE))", innerConditions))
+			values = append(values, innerValues...)
 		default:
 			if !isValidPostgresIdentifier(key) {
 				return "", nil, fmt.Errorf("invalid column name: %s", key)
@@ -148,6 +162,8 @@ func (c *Converter) convertFilter(filter map[string]any, paramIndex int) (string
 						return "", nil, fmt.Errorf("$or as scalar operator not supported")
 					case "$and":
 						return "", nil, fmt.Errorf("$and as scalar operator not supported")
+					case "$not":
+						return "", nil, fmt.Errorf("$not as scalar operator not supported")
 					case "$in":
 						if !isScalarSlice(v[operator]) {
 							return "", nil, fmt.Errorf("invalid value for $in operator (must array of primatives): %v", v[operator])

filter/converter_test.go

@@ -224,6 +224,30 @@ func TestConverter_Convert(t *testing.T) {
 			nil,
 			fmt.Errorf("invalid column name: \"bla = 1 --"),
 		},
+		{
+			"$not operator",
+			nil,
+			`{"$not": {"name": "John"}}`,
+			`(NOT COALESCE(("name" = $1), FALSE))`,
+			[]any{"John"},
+			nil,
+		},
+		{
+			"$not in the wrong place",
+			nil,
+			`{"name": {"$not": {"$eq": "John"}}}`,
+			``,
+			nil,
+			fmt.Errorf("$not as scalar operator not supported"),
+		},
+		{
+			"$not with a scalar",
+			nil,
+			`{"$not": "John"}`,
+			``,
+			nil,
+			fmt.Errorf("invalid value for $not operator (must be object): John"),
+		},
 	}
 
 	for _, tt := range tests {

fuzz/fuzz_test.go

@@ -37,6 +37,8 @@ func FuzzConverter(f *testing.F) {
 		`{"status": {"$in": []}}`,
 		`{"$or": [{}, {}]}`,
 		`{"\"bla = 1 --": 1}`,
+		`{"$not": {"name": "John"}}`,
+		`{"name": {"$not": {"$eq": "John"}}}`,
 	}
 	for _, tc := range tcs {
 		f.Add(tc, true)

integration/postgres_test.go

@@ -309,6 +309,18 @@ func TestIntegration_BasicOperators(t *testing.T) {
 			[]int{3, 4, 5, 6, 7, 8, 9, 10},
 			nil,
 		},
+		{
+			`$not on jsonb column`,
+			`{"$not": {"pet": "cat"}}`,
+			[]int{1, 3, 5, 7, 9, 10},
+			nil,
+		},
+		{
+			`$not on normal column`,
+			`{"$not": {"mount": "horse"}}`,
+			[]int{3, 4, 5, 6, 7, 8, 9, 10},
+			nil,
+		},
 	}
 
 	for _, tt := range tests {