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# package community: Fix SQLChatMessageHistory ## Description Here is a rewrite of `SQLChatMessageHistory` to properly implement the asynchronous approach. The code circumvents [issue 22021](https://github.com/langchain-ai/langchain/issues/22021) by accepting a synchronous call to `def add_messages()` in an asynchronous scenario. This bypasses the bug. For the same reasons as in [PR 22](https://github.com/langchain-ai/langchain-postgres/pull/32) of `langchain-postgres`, we use a lazy strategy for table creation. Indeed, the promise of the constructor cannot be fulfilled without this. It is not possible to invoke a synchronous call in a constructor. We compensate for this by waiting for the next asynchronous method call to create the table. The goal of the `PostgresChatMessageHistory` class (in `langchain-postgres`) is, among other things, to be able to recycle database connections. The implementation of the class is problematic, as we have demonstrated in [issue 22021](https://github.com/langchain-ai/langchain/issues/22021). Our new implementation of `SQLChatMessageHistory` achieves this by using a singleton of type (`Async`)`Engine` for the database connection. The connection pool is managed by this singleton, and the code is then reentrant. We also accept the type `str` (optionally complemented by `async_mode`. I know you don't like this much, but it's the only way to allow an asynchronous connection string). In order to unify the different classes handling database connections, we have renamed `connection_string` to `connection`, and `Session` to `session_maker`. Now, a single transaction is used to add a list of messages. Thus, a crash during this write operation will not leave the database in an unstable state with a partially added message list. This makes the code resilient. We believe that the `PostgresChatMessageHistory` class is no longer necessary and can be replaced by: ``` PostgresChatMessageHistory = SQLChatMessageHistory ``` This also fixes the bug. ## Issue - [issue 22021](https://github.com/langchain-ai/langchain/issues/22021) - Bug in _exit_history() - Bugs in PostgresChatMessageHistory and sync usage - Bugs in PostgresChatMessageHistory and async usage - [issue 36](https://github.com/langchain-ai/langchain-postgres/issues/36) ## Twitter handle: pprados ## Tests - libs/community/tests/unit_tests/chat_message_histories/test_sql.py (add async test) @baskaryan, @eyurtsev or @hwchase17 can you check this PR ? And, I've been waiting a long time for validation from other PRs. Can you take a look? - [PR 32](https://github.com/langchain-ai/langchain-postgres/pull/32) - [PR 15575](https://github.com/langchain-ai/langchain/pull/15575) - [PR 13200](https://github.com/langchain-ai/langchain/pull/13200) --------- Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com> |
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🦜️🧑🤝🧑 LangChain Community
Quick Install
pip install langchain-community
What is it?
LangChain Community contains third-party integrations that implement the base interfaces defined in LangChain Core, making them ready-to-use in any LangChain application.
For full documentation see the API reference.
📕 Releases & Versioning
langchain-community is currently on version 0.0.x
All changes will be accompanied by a patch version increase.
💁 Contributing
As an open-source project in a rapidly developing field, we are extremely open to contributions, whether it be in the form of a new feature, improved infrastructure, or better documentation.
For detailed information on how to contribute, see the Contributing Guide.