Add is not null to query builder

gqlalchemy/query_builders/declarative_base.py

@@ -30,7 +30,13 @@
 from gqlalchemy.graph_algorithms.integrated_algorithms import IntegratedAlgorithm
 from gqlalchemy.vendors.memgraph import Memgraph
 from gqlalchemy.models import Node, Relationship
-from gqlalchemy.utilities import to_cypher_labels, to_cypher_properties, to_cypher_value, to_cypher_qm_arguments
+from gqlalchemy.utilities import (
+    to_cypher_labels,
+    to_cypher_properties,
+    to_cypher_value,
+    to_cypher_qm_arguments,
+    to_null_operator,
+)
 from gqlalchemy.vendors.database_client import DatabaseClient
 
 
@@ -186,7 +192,7 @@ def _build_where_query(self, item: str, operator: Operator, **kwargs) -> "Declar
 
         if value is None:
             if literal is None:
-                raise GQLAlchemyLiteralAndExpressionMissing(clause=self.type)
+                operator_str = to_null_operator(operator_str)
 
             value = to_cypher_value(literal)
         elif literal is not None:

gqlalchemy/utilities.py

@@ -84,10 +84,20 @@ def _is_torch_tensor(value):
     return False
 
 
+def to_null_operator(value: str) -> str:
+    if value == "=":
+        return "IS"
+    if value == "!=" or value == "<>":
+        return "IS NOT"
+    raise InvalidOperatorException(f"Operator {value} can not be used with None")
+
+
 def to_cypher_value(value: Any, config: NetworkXCypherConfig = None) -> str:
     """Converts value to a valid Cypher type."""
     if config is None:
         config = NetworkXCypherConfig()
+    if value is None:
+        return "null"
 
     value_type = type(value)
 
@@ -264,3 +274,7 @@ def __str__(self) -> str:
 
 class NanException(Exception):
     pass
+
+
+class InvalidOperatorException(Exception):
+    pass

tests/query_builders/test_query_builders.py

@@ -358,6 +358,26 @@ def test_where_property(self, vendor):
 
         mock.assert_called_with(expected_query)
 
+    @pytest.mark.parametrize("operator", ["<>", "!=", "="])
+    def test_where_property_null_operators(self, vendor, operator):
+        query_builder = (
+            vendor[1]
+            .match()
+            .node(labels="L1", variable="n")
+            .to(relationship_type="TO")
+            .node(labels="L2", variable="m")
+            .where(item="n.name", operator=operator, literal=None)
+            .return_()
+        )
+        expected_query = (
+            f" MATCH (n:L1)-[:TO]->(m:L2) WHERE n.name IS {'NOT ' if operator != '=' else ''}null RETURN * "
+        )
+
+        with patch.object(vendor[0], "execute_and_fetch", return_value=None) as mock:
+            query_builder.execute()
+
+        mock.assert_called_with(expected_query)
+
     def test_where_not_property(self, vendor):
         query_builder = (
             vendor[1]