fix: add write messages to Chat History (#265)

* fix: add write definition for messages property in Chat History

* chore: add test for setting messages property in Chat History

* chore: lint fix

Author: vishwarajanand

src/langchain_google_cloud_sql_pg/chat_message_history.py

@@ -106,11 +106,17 @@ def create_sync(
         history = engine._run_as_sync(coro)
         return cls(cls.__create_key, engine, history)
 
-    @property  # type: ignore[override]
+    @property
     def messages(self) -> list[BaseMessage]:
-        """The abstraction required a property."""
+        """Fetches all messages stored in AlloyDB."""
         return self._engine._run_as_sync(self._history._aget_messages())
 
+    @messages.setter
+    def messages(self, value: list[BaseMessage]) -> None:
+        """Clear the stored messages and appends a list of messages to the record in AlloyDB."""
+        self.clear()
+        self.add_messages(value)
+
     async def aadd_message(self, message: BaseMessage) -> None:
         """Append the message to the record in PostgreSQL"""
         await self._engine._run_as_async(self._history.aadd_message(message))

tests/test_chatmessagehistory.py

@@ -163,6 +163,20 @@ async def test_chat_message_history_sync_messages(
     assert len(history2.messages) == 0
 
 
+@pytest.mark.asyncio
+async def test_chat_message_history_set_messages(
+    async_engine: PostgresEngine,
+) -> None:
+    history = await PostgresChatMessageHistory.create(
+        engine=async_engine, session_id="test", table_name=table_name_async
+    )
+    msg1 = HumanMessage(content="hi!")
+    msg2 = AIMessage(content="bye -_-")
+    # verify setting messages property adds to message history
+    history.messages = [msg1, msg2]
+    assert len(history.messages) == 2
+
+
 @pytest.mark.asyncio
 async def test_chat_table_async(async_engine):
     with pytest.raises(ValueError):