从 ConversationalChain 迁移

ConversationChain 结合了先前消息的记忆，以维持有状态的对话。

切换到 LCEL 实现的一些优点包括：

• 天生支持线程/独立会话。要使其与 ConversationChain 一起工作，您需要在链外实例化一个单独的内存类。
• 更明确的参数。ConversationChain 包含一个隐藏的默认提示，这可能会导致混淆。
• 支持流式传输。ConversationChain 仅通过回调支持流式传输。

RunnableWithMessageHistory 通过配置参数实现会话。它应该与返回 聊天消息历史 的可调用对象一起实例化。默认情况下，它期望此函数接受一个参数 session_id。

%pip install --upgrade --quiet langchain langchain-openai

import os
from getpass import getpass

os.environ["OPENAI_API_KEY"] = getpass()

旧版

from langchain.chains import ConversationChain
from langchain.memory import ConversationBufferMemory
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI

template = """
You are a pirate. Answer the following questions as best you can.
Chat history: {history}
Question: {input}
"""

prompt = ChatPromptTemplate.from_template(template)

memory = ConversationBufferMemory()

chain = ConversationChain(
    llm=ChatOpenAI(),
    memory=memory,
    prompt=prompt,
)

chain({"input": "how are you?"})

{'input': 'how are you?',
 'history': '',
 'response': "Arr matey, I be doin' well on the high seas, plunderin' and pillagin' as usual. How be ye?"}

LCEL

from langchain_core.chat_history import InMemoryChatMessageHistory
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain_openai import ChatOpenAI

prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "You are a pirate. Answer the following questions as best you can."),
        ("placeholder", "{chat_history}"),
        ("human", "{input}"),
    ]
)

history = InMemoryChatMessageHistory()


def get_history():
    return history


chain = prompt | ChatOpenAI() | StrOutputParser()

wrapped_chain = RunnableWithMessageHistory(
    chain,
    get_history,
    history_messages_key="chat_history",
)

wrapped_chain.invoke({"input": "how are you?"})

"Arr, me matey! I be doin' well, sailin' the high seas and searchin' for treasure. How be ye?"

上述示例对所有会话使用相同的 history。下面的示例演示如何为每个会话使用不同的聊天历史。

from langchain_core.chat_history import BaseChatMessageHistory
from langchain_core.runnables.history import RunnableWithMessageHistory

store = {}


def get_session_history(session_id: str) -> BaseChatMessageHistory:
    if session_id not in store:
        store[session_id] = InMemoryChatMessageHistory()
    return store[session_id]


chain = prompt | ChatOpenAI() | StrOutputParser()

wrapped_chain = RunnableWithMessageHistory(
    chain,
    get_session_history,
    history_messages_key="chat_history",
)

wrapped_chain.invoke(
    {"input": "Hello!"},
    config={"configurable": {"session_id": "abc123"}},
)

'Ahoy there, me hearty! What can this old pirate do for ye today?'

下一步

查看本教程，获取有关使用RunnableWithMessageHistory的更完整的构建指南。

查看LCEL 概念文档，以获取更多背景信息。