函数 entrypoint

使用 entrypoint 函数定义 LangGraph 工作流。

函数签名

封装函数最多必须接受两个参数。第一个参数是函数的输入。第二个（可选）参数是 LangGraphRunnableConfig 对象。如果您希望向函数传递多个参数，可以将其作为对象传递。

辅助函数

流式传输

要将数据写入“自定义”流，请使用 getWriter 函数，或使用 LangGraphRunnableConfig.writer 属性。

状态管理

可以使用 getPreviousState 函数来访问在同一线程 ID 上上次调用 entrypoint 时返回的先前状态。

如果您希望保存除返回值以外的状态，可以使用 entrypoint.final 函数。

示例：使用 entrypoint 和 tasks

import { task, entrypoint } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";
import { interrupt, Command } from "@langchain/langgraph";

const composeEssay = task("compose", async (topic: string) => {
  await new Promise(r => setTimeout(r, 1000)); // Simulate slow operation
  return `An essay about ${topic}`;
});

const reviewWorkflow = entrypoint({
  name: "review",
  checkpointer: new MemorySaver()
}, async (topic: string) => {
  const essay = await composeEssay(topic);
  const humanReview = await interrupt({
    question: "Please provide a review",
    essay
  });
  return {
    essay,
    review: humanReview
  };
});

// Example configuration for the workflow
const config = {
  configurable: {
    thread_id: "some_thread"
  }
};

// Topic for the essay
const topic = "cats";

// Stream the workflow to generate the essay and await human review
for await (const result of reviewWorkflow.stream(topic, config)) {
  console.log(result);
}

// Example human review provided after the interrupt
const humanReview = "This essay is great.";

// Resume the workflow with the provided human review
for await (const result of reviewWorkflow.stream(new Command({ resume: humanReview }), config)) {
  console.log(result);
}
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示例：访问上一个返回值

import { entrypoint, getPreviousState } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";

const accumulator = entrypoint({
  name: "accumulator",
  checkpointer: new MemorySaver()
}, async (input: string) => {
  const previous = getPreviousState<number>();
  return previous !== undefined ? `${previous } ${input}` : input;
});

const config = {
  configurable: {
    thread_id: "some_thread"
  }
};
await accumulator.invoke("hello", config); // returns "hello"
await accumulator.invoke("world", config); // returns "hello world"
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示例：使用 entrypoint.final 保存值

import { entrypoint, getPreviousState } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";

const myWorkflow = entrypoint({
  name: "accumulator",
  checkpointer: new MemorySaver()
}, async (num: number) => {
  const previous = getPreviousState<number>();

  // This will return the previous value to the caller, saving
  // 2 * num to the checkpoint, which will be used in the next invocation
  // for the `previous` parameter.
  return entrypoint.final({
    value: previous ?? 0,
    save: 2 * num
  });
});

const config = {
  configurable: {
    thread_id: "some_thread"
  }
};

await myWorkflow.invoke(3, config); // 0 (previous was undefined)
await myWorkflow.invoke(1, config); // 6 (previous was 3 * 2 from the previous invocation)
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