使用时间旅行

当与基于模型进行决策的非确定性系统（例如由LLM驱动的智能体）一起工作时，详细检查其决策过程可能很有用：

1. 理解推理：分析导致成功结果的过程步骤。
2. 调试错误：确定错误发生的位置和原因。
3. 探索替代方案：测试不同的路径以发现更好的解决方案。

LangGraph提供了时间旅行功能以支持这些用例。具体来说，您可以从先前的检查点恢复执行——要么重新播放相同的状态，要么修改它以探索替代方案。在所有情况下，恢复过去的执行都会在历史中产生一个新的分支。

要使用 LangGraph 中的 时间旅行：

1. 使用invoke或stream方法，以初始输入运行图。
2. 在现有线程中识别一个检查点：使用getStateHistory()方法检索特定thread_id的执行历史并定位所需的checkpoint_id。或者，在希望执行暂停的节点之前设置断点。然后您可以找到记录到该断点的最近检查点。
3. 更新图状态（可选）：使用updateState方法在检查点修改图的状态并从替代状态恢复执行。
4. 从检查点恢复执行：使用invoke或stream方法，输入null，并包含适当的thread_id和checkpoint_id的配置。

关于时间旅行的概念概述，请参阅时间旅行。

在工作流中

本示例构建了一个简单的LangGraph工作流程，该工作流程生成一个笑话主题并使用LLM编写笑话。它演示了如何运行图、检索过去的执行检查点、可选地修改状态，并从选定的检查点恢复执行以探索不同的结果。

设置

首先，我们需要安装所需的软件包

npm install @langchain/langgraph @langchain/anthropic

接下来，我们需要为Anthropic（我们将使用的LLM）设置API密钥

process.env.ANTHROPIC_API_KEY = "YOUR_API_KEY";

在 LangSmith 上注册，快速发现问题和提升您的 LangGraph 项目性能。LangSmith 允许您使用跟踪数据来调试、测试和监控使用 LangGraph 构建的 LLM 应用程序。

import { v4 as uuidv4 } from "uuid";
import * as z from "zod";
import { StateGraph, START, END } from "@langchain/langgraph";
import { ChatAnthropic } from "@langchain/anthropic";
import { MemorySaver } from "@langchain/langgraph";

const State = z.object({
  topic: z.string().optional(),
  joke: z.string().optional(),
});

const model = new ChatAnthropic({
  model: "claude-sonnet-4-5",
  temperature: 0,
});

// Build workflow
const workflow = new StateGraph(State)
  // Add nodes
  .addNode("generateTopic", async (state) => {
    // LLM call to generate a topic for the joke
    const msg = await model.invoke("Give me a funny topic for a joke");
    return { topic: msg.content };
  })
  .addNode("writeJoke", async (state) => {
    // LLM call to write a joke based on the topic
    const msg = await model.invoke(`Write a short joke about ${state.topic}`);
    return { joke: msg.content };
  })
  // Add edges to connect nodes
  .addEdge(START, "generateTopic")
  .addEdge("generateTopic", "writeJoke")
  .addEdge("writeJoke", END);

// Compile
const checkpointer = new MemorySaver();
const graph = workflow.compile({ checkpointer });

1. 运行图

const config = {
  configurable: {
    thread_id: uuidv4(),
  },
};

const state = await graph.invoke({}, config);

console.log(state.topic);
console.log();
console.log(state.joke);

输出：

How about "The Secret Life of Socks in the Dryer"? You know, exploring the mysterious phenomenon of how socks go into the laundry as pairs but come out as singles. Where do they go? Are they starting new lives elsewhere? Is there a sock paradise we don't know about? There's a lot of comedic potential in the everyday mystery that unites us all!

# The Secret Life of Socks in the Dryer

I finally discovered where all my missing socks go after the dryer. Turns out they're not missing at all—they've just eloped with someone else's socks from the laundromat to start new lives together.

My blue argyle is now living in Bermuda with a red polka dot, posting vacation photos on Sockstagram and sending me lint as alimony.

2. 识别检查点

// The states are returned in reverse chronological order.
const states = [];
for await (const state of graph.getStateHistory(config)) {
  states.push(state);
}

for (const state of states) {
  console.log(state.next);
  console.log(state.config.configurable?.checkpoint_id);
  console.log();
}

输出：

[]
1f02ac4a-ec9f-6524-8002-8f7b0bbeed0e

['writeJoke']
1f02ac4a-ce2a-6494-8001-cb2e2d651227

['generateTopic']
1f02ac4a-a4e0-630d-8000-b73c254ba748

['__start__']
1f02ac4a-a4dd-665e-bfff-e6c8c44315d9

// This is the state before last (states are listed in chronological order)
const selectedState = states[1];
console.log(selectedState.next);
console.log(selectedState.values);

输出：

['writeJoke']
{'topic': 'How about "The Secret Life of Socks in the Dryer"? You know, exploring the mysterious phenomenon of how socks go into the laundry as pairs but come out as singles. Where do they go? Are they starting new lives elsewhere? Is there a sock paradise we don\\'t know about? There\\'s a lot of comedic potential in the everyday mystery that unites us all!'}

3. 更新状态

updateState 将创建一个新的检查点。新的检查点将与相同的线程相关联，但具有新的检查点ID。

const newConfig = await graph.updateState(selectedState.config, {
  topic: "chickens",
});
console.log(newConfig);

输出：

{'configurable': {'thread_id': 'c62e2e03-c27b-4cb6-8cea-ea9bfedae006', 'checkpoint_ns': '', 'checkpoint_id': '1f02ac4a-ecee-600b-8002-a1d21df32e4c'}}

4. 从检查点恢复执行

await graph.invoke(null, newConfig);

输出：

{
  'topic': 'chickens',
  'joke': 'Why did the chicken join a band?\n\nBecause it had excellent drumsticks!'
}

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