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子图

子图是一个用作另一个图中的节点的图——这是应用于 LangGraph 的封装概念。子图允许您构建包含多个组件(这些组件本身就是图)的复杂系统。

Subgraph

使用子图的一些原因包括

  • 构建多智能体系统
  • 当您想在多个图中重用一组节点时
  • 当您希望不同团队独立地处理图的不同部分时,您可以将每个部分定义为子图,只要子图接口(输入和输出模式)得到遵守,父图就可以在不了解子图任何细节的情况下构建

添加子图时的主要问题是父图和子图如何通信,即它们在图执行期间如何相互传递状态。有两种情况

  • 父图和子图在其状态模式中具有共享状态键。在这种情况下,您可以将子图作为节点包含在父图中

    from langgraph.graph import StateGraph, MessagesState, START
    
    # Subgraph
    
    def call_model(state: MessagesState):
        response = model.invoke(state["messages"])
        return {"messages": response}
    
    subgraph_builder = StateGraph(State)
    subgraph_builder.add_node(call_model)
    ...
    subgraph = subgraph_builder.compile()
    
    # Parent graph
    
    builder = StateGraph(State)
    builder.add_node("subgraph_node", subgraph)
    builder.add_edge(START, "subgraph_node")
    graph = builder.compile()
    ...
    graph.invoke({"messages": [{"role": "user", "content": "hi!"}]})
    
  • 父图和子图具有不同的模式(其状态模式中没有共享状态键)。在这种情况下,您必须从父图中的节点内部调用子图:当父图和子图具有不同的状态模式,并且您需要在调用子图之前或之后转换状态时,这很有用

    from typing_extensions import TypedDict, Annotated
    from langchain_core.messages import AnyMessage
    from langgraph.graph import StateGraph, MessagesState, START
    from langgraph.graph.message import add_messages
    
    class SubgraphMessagesState(TypedDict):
        subgraph_messages: Annotated[list[AnyMessage], add_messages]
    
    # Subgraph
    
    def call_model(state: SubgraphMessagesState):
        response = model.invoke(state["subgraph_messages"])
        return {"subgraph_messages": response}
    
    subgraph_builder = StateGraph(SubgraphMessagesState)
    subgraph_builder.add_node("call_model_from_subgraph", call_model)
    subgraph_builder.add_edge(START, "call_model_from_subgraph")
    ...
    subgraph = subgraph_builder.compile()
    
    # Parent graph
    
    def call_subgraph(state: MessagesState):
        response = subgraph.invoke({"subgraph_messages": state["messages"]})
        return {"messages": response["subgraph_messages"]}
    
    builder = StateGraph(State)
    builder.add_node("subgraph_node", call_subgraph)
    builder.add_edge(START, "subgraph_node")
    graph = builder.compile()
    ...
    graph.invoke({"messages": [{"role": "user", "content": "hi!"}]})