Adding timestamp in additional args

memory.py

@@ -34,10 +34,10 @@ class CustomMongoDBChatMessageHistory(MongoDBChatMessageHistory):
         return messages
 
     def add_user_message(self, message: str) -> None:
-        self.append(HumanMessage(content=message))
+        self.append(HumanMessage(content=message, additional_kwargs={"timestamp": datetime.utcnow()}))
 
     def add_ai_message(self, message: str) -> None:
-        self.append(AIMessage(content=message))
+        self.append(AIMessage(content=message, additional_kwargs={"timestamp": datetime.utcnow()}))
 
     def append(self, message: BaseMessage) -> None:
         """Append the message to the record in MongoDB with the desired format"""
@@ -56,7 +56,7 @@ class CustomMongoDBChatMessageHistory(MongoDBChatMessageHistory):
             # Update the messages array with the new message object
             self.collection.update_one(
                 {"SessionId": self.session_id},
-                {"$push": {"messages": json.dumps(_message_to_dict(message))}},
+                {"$push": {"messages": json.dumps(_message_to_dict(message), default=str)}},
                 upsert=True
             )
         except errors.WriteError as err: