AsyncMongoClient support for MongoDBChatMessageHistory

[BParvatkar]

I am trying to use AsyncMongoClient for MongoDBChatMessageHistory.

def get_chat_history(client: AsyncMongoClient, session_id: str) -> MongoDBChatMessageHistory:
    return MongoDBChatMessageHistory(
        connection_string=None,
        session_id=session_id,
        client=client,
        database_name="db",
        collection_name="conversation",
    )


prompt = ChatPromptTemplate.from_messages(
        [
            ("system", "You're an assistant"),
            MessagesPlaceholder("history"),
            ("human", "{input}"),
        ]
    )

    llm = ChatBedrockConverse(
        model_id="model_id", region_name="region_name", provider="provider"
    )
    chain = prompt | llm
    chain_with_history = RunnableWithMessageHistory(
        chain,
        get_session_history=lambda session_id: get_chat_history(client, session_id),
        input_messages_key="input",
        history_messages_key="history",
    )

Console message

/Users/mongodb-setup/.venv/lib/python3.12/site-packages/langchain_mongodb/chat_message_histories.py:169: RuntimeWarning: coroutine 'AsyncCollection.insert_one' was never awaited
  self.collection.insert_one(
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

I saw that MongoDBChatMessageHistory expects MongoClient and not AsyncMongoClient. Is there a way to use it? Or the support isnt available yet?

[blink1073]

HI @BParvatkar, we intentionally only support the synchronous MongoClient across all of the APIs in this library. We are in fact removing the AsyncSqliteSaver class in next release of langgraph-checkpointer-mongodb. The pattern we are using is to have async methods on our classes to support async users. The alternative would be to have duplicate logic for all of the classes, which we originally did for AsyncSqliteSaver, but it proved to be difficult to maintain and we did not want to repeat the pattern for all classes.

[BParvatkar]

Is there a working example on how this can be used? Probably with RunnableWithMessageHistory

[blink1073]

The base class of MongoDBChatMessageHistory has async methods that call the synchronous methods in an executor: https://github.com/langchain-ai/langchain/blob/986302322f1077122434ff09914e8ce23e03cbc5/libs/core/langchain_core/chat_history.py#L116.

So, you can use a synchronous client, and then call the async methods on RunnableWithMessageHistory, such as ainvoke.

[BParvatkar]

Thanks. I will check it out. Also, one more question. MongoDBChatMessageHistory does not provide an option to send ClientSession. How are transactions supported? I want to rollback changes based on certain criteria after receiving messages. Currently, I have defined a wrapper that overrides the session property after it is initialized.

[blink1073]

That is a good call-out, we do not yet support transactions. I've opened https://jira.mongodb.org/browse/INTPYTHON-774 to track that feature, and https://jira.mongodb.org/browse/INTPYTHON-773 to track making async usage more obvious.