MongoDB is a source-available cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with optional schemas. MongoDB is developed by MongoDB Inc. and licensed under the Server Side Public License (SSPL). - Wikipedia
This notebook goes over how to use the MongoDBChatMessageHistory class to store chat message history in a Mongodb database.

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Setup

The integration lives in the langchain-mongodb package, so we need to install that. 
pip install -qU langchain-mongodb
It’s also helpful (but not needed) to set up LangSmith for best-in-class observability 
# os.environ["LANGSMITH_TRACING"] = "true"
# os.environ["LANGSMITH_API_KEY"] = getpass.getpass()

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Usage

To use the storage you need to provide only 2 things:
  1. Session Id - a unique identifier of the session, like user name, email, chat id etc.
  2. Connection string - a string that specifies the database connection. It will be passed to MongoDB create_engine function.
If you want to customize where the chat histories go, you can also pass:
  1. database_name - name of the database to use
  2. collection_name - collection to use within that database
from langchain_mongodb.chat_message_histories import MongoDBChatMessageHistory

chat_message_history = MongoDBChatMessageHistory(
    session_id="test_session",
    connection_string="mongodb://mongo_user:password123@mongo:27017",
    database_name="my_db",
    collection_name="chat_histories",
)

chat_message_history.add_user_message("Hello")
chat_message_history.add_ai_message("Hi")

chat_message_history.messages

[HumanMessage(content='Hello'), AIMessage(content='Hi')]

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Chaining

We can easily combine this message history class with LCEL Runnables To do this we will want to use OpenAI, so we need to install that. You will also need to set the OPENAI_API_KEY environment variable to your OpenAI key. 
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain_openai import ChatOpenAI

import os

assert os.environ["OPENAI_API_KEY"], (
    "Set the OPENAI_API_KEY environment variable with your OpenAI API key."
)

prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "You are a helpful assistant."),
        MessagesPlaceholder(variable_name="history"),
        ("human", "{question}"),
    ]
)

chain = prompt | ChatOpenAI()

chain_with_history = RunnableWithMessageHistory(
    chain,
    lambda session_id: MongoDBChatMessageHistory(
        session_id=session_id,
        connection_string="mongodb://mongo_user:password123@mongo:27017",
        database_name="my_db",
        collection_name="chat_histories",
    ),
    input_messages_key="question",
    history_messages_key="history",
)

# This is where we configure the session id
config = {"configurable": {"session_id": "<SESSION_ID>"}}

chain_with_history.invoke({"question": "Hi! I'm bob"}, config=config)

AIMessage(content='Hi Bob! How can I assist you today?')

chain_with_history.invoke({"question": "Whats my name"}, config=config)

AIMessage(content='Your name is Bob. Is there anything else I can help you with, Bob?')