Fix CREATE_SESSION_NODE_QUERY (#378)

* Fix CREATE_SESSION_NODE_QUERY

* Add test

* Update CHANGELOG

Author: stellasia

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Next
 
+### Fixed
+
+- Fixed a bug where Session nodes were duplicated.
+
 ## 1.8.0
 
 ### Added

src/neo4j_graphrag/message_history.py

@@ -26,7 +26,9 @@
 )
 
 CREATE_SESSION_NODE_QUERY = (
-    "MERGE (s:`{node_label}` {{id:$session_id, createdAt: datetime()}})"
+    "MERGE (s:`{node_label}` {{id:$session_id}}) "
+    "ON CREATE SET s.createdAt=datetime() "
+    "ON MATCH SET s.updatedAt=datetime() "
 )
 
 DELETE_SESSION_AND_MESSAGES_QUERY = (

tests/e2e/test_message_history_e2e.py

@@ -136,3 +136,18 @@ def test_neo4j_message_window_size(driver: neo4j.Driver) -> None:
         == "I'd be happy to help you find the perfect car."
     )
     assert message_history.messages[0]["role"] == "assistant"
+
+
+def test_neo4j_message_history_session_id_unique(driver: neo4j.Driver) -> None:
+    driver.execute_query(query_="MATCH (n) DETACH DELETE n;")
+    Neo4jMessageHistory(session_id="123", driver=driver)
+    Neo4jMessageHistory(session_id="123", driver=driver)
+
+    results = driver.execute_query(
+        query_="MATCH (s:`Session`) WHERE s.id = '123' RETURN s"
+    )
+    records = results.records
+    assert len(records) == 1
+    session = records[0]["s"]
+    assert session.get("createdAt") is not None
+    assert session.get("updatedAt") is not None