子图

子图是作为另一个图中节点使用的图——这是应用于 LangGraph 的封装概念。子图允许你构建具有多个组件的复杂系统，而这些组件本身也是图。

使用子图的一些原因是：

• 构建多智能代理系统
• 当你想在多个图中重用一组节点时
• 当你希望不同团队独立处理图的不同部分时，你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，父图就可以在不知道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。有两种场景：

• 父图和子图在其状态模式中有**共享状态键**。在这种情况下，你可以将子图作为父图中的节点包含

=== "Python"

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)
...
# highlight-next-line
subgraph = subgraph_builder.compile()

# Parent graph

builder = StateGraph(State)
# highlight-next-line
builder.add_node("subgraph_node", subgraph)
builder.add_edge(START, "subgraph_node")
graph = builder.compile()
...
graph.invoke({"messages": [{"role": "user", "content": "hi!"}]})

=== "JavaScript"

import { StateGraph, MessagesZodState, START } from "@langchain/langgraph";

// Subgraph

const subgraphBuilder = new StateGraph(MessagesZodState).addNode(
  "callModel",
  async (state) => {
    const response = await model.invoke(state.messages);
    return { messages: response };
  }
);
// ... other nodes and edges
// highlight-next-line
const subgraph = subgraphBuilder.compile();

// Parent graph

const builder = new StateGraph(MessagesZodState)
  // highlight-next-line
  .addNode("subgraphNode", subgraph)
  .addEdge(START, "subgraphNode");
const graph = builder.compile();
// ...
await graph.invoke({ messages: [{ role: "user", content: "hi!" }] });

• 父图和子图有**不同的模式**（在其状态模式中没有共享状态键）。在这种情况下，你必须从父图中的节点内部调用子图：当父图和子图有不同的状态模式，并且你需要在调用子图之前或之后转换状态时，这很有用

=== "Python"

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):
    # highlight-next-line
    subgraph_messages: Annotated[list[AnyMessage], add_messages]

# Subgraph

# highlight-next-line
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")
...
# highlight-next-line
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)
# highlight-next-line
builder.add_node("subgraph_node", call_subgraph)
builder.add_edge(START, "subgraph_node")
graph = builder.compile()
...
graph.invoke({"messages": [{"role": "user", "content": "hi!"}]})

=== "JavaScript"

import { StateGraph, MessagesZodState, START } from "@langchain/langgraph";
import { z } from "zod";

const SubgraphState = z.object({
  // highlight-next-line
  subgraphMessages: MessagesZodState.shape.messages,
});

// Subgraph

const subgraphBuilder = new StateGraph(SubgraphState)
  // highlight-next-line
  .addNode("callModelFromSubgraph", async (state) => {
    const response = await model.invoke(state.subgraphMessages);
    return { subgraphMessages: response };
  })
  .addEdge(START, "callModelFromSubgraph");
// ...
// highlight-next-line
const subgraph = subgraphBuilder.compile();

// Parent graph

const builder = new StateGraph(MessagesZodState)
  // highlight-next-line
  .addNode("subgraphNode", async (state) => {
    const response = await subgraph.invoke({
      subgraphMessages: state.messages,
    });
    return { messages: response.subgraphMessages };
  })
  .addEdge(START, "subgraphNode");
const graph = builder.compile();
// ...
await graph.invoke({ messages: [{ role: "user", content: "hi!" }] });