Complete context compression through middleware

OSS Product Help LangChain
,
1 
I am trying to use middleware to summarize and compress context. But it is appended by default. If I want to override it, what should I do? This is my code; it is appended by default.

from langchain.agents.middleware import before_model
from langchain_core.messages import SystemMessage

from model.llm.deepseek.deepseek_llm import deepseek


@before_model
def summary_messages(state,runtime):
    print(state["messages"])
    print(len(state["messages"]))
    if len(state["messages"]) > 20:
        result = deepseek.invoke(
            f"总结一下对话记录生成概要{state['messages']}"
        )
        return {"messages":[result]}
    return None
2

there are some built-in middleware - why not using them? :slight_smile: Prebuilt middleware - Docs by LangChain

3

if you want your own middleware, use RemoveMessage(id=REMOVE_ALL_MESSAGES) before the new messages to clear the existing state, then add the summary + recent messages:

return {
    "messages": [
        RemoveMessage(id=REMOVE_ALL_MESSAGES),
        HumanMessage(content=f"Summary:\n\n{result.content}"),
        *messages[-5:],
    ]
}

summarize all messages except the last 5