当前位置：首页 > news >正文

[LangChain] 19. 持久化记忆

news 2026/3/27 0:37:43

目前我们所使用的 Memory，大多只存在于内存中，一旦进程关闭、用户刷新页面，所有历史对话都会丢失。实际项目中，我们常常希望：

让用户“第二次回来”还能接着上次对话继续聊
将多轮聊天记录保存在本地或数据库中，用于分析、审计、训练、回溯

这时候，我们就需要将 Memory 做持久化操作，从而实现“记忆不丢失”。

要进行持久化操作，无非就两种方式：

存储至文件
存储至数据库

课堂练习：手动封装一个做持久化处理的 FileChatMessageHistory 类。

import { BaseListChatMessageHistory } from "@langchain/core/chat_history";
import fs from "fs/promises";
import { AIMessage, HumanMessage } from "langchain";
import path from "path";export class FileChatMessageHistory extends BaseListChatMessageHistory {constructor(filepath) {super();this.filepath = filepath;this._q = Promise.resolve();}_enqueue(fn) {const run = () => fn();const p = this._q.then(run, run);this.q = p.catch(() => {});return p;}async _ensureDir() {await fs.mkdir(path.dirname(this.filepath), { recursive: true });}async _atomicWrite(text) {await this._ensureDir();const tmp = `.tmp-${Date.now()}-${Math.random().toString(36).substring(2)}`;await fs.writeFile(tmp, text, "utf8");await fs.rename(tmp, this.filepath);}async _readRaw() {// "[{type: 'human', content: 'xxxx'},{type: 'ai', content: 'xxxx}]"try {const txt = await fs.readFile(this.filepath, "utf8");const arr = JSON.parse(txt);return Array.isArray(arr) ? arr : [];} catch (e) {if (e && e.code === "ENOENT") return [];if (e instanceof SyntaxError) {console.warn(`历史文件损坏，已忽略：${this.filepath}`);return [];}throw e;}}async _saveMessages(messages) {const raw = messages.map((m) => ({type: m.type,content: m.content,}));await this._atomicWrite(JSON.stringify(raw, null, 2));}// 下面的方法就是对外的接口async getMessages() {const raw = await this._readRaw(); // 从文件中进行读取return raw.map((r) =>r.type === "human"? new HumanMessage(r.content): new AIMessage(r.content));}/*** 添加一条消息* @param {*} message 消息对象*/async addMessage(message) {return this._enqueue(async () => {const msgs = await this.getMessages();msgs.push(message);await this._saveMessages(msgs);});}async addMessages(messages) {return this._enqueue(async () => {const msgs = await this.getMessages();msgs.push(...messages);await this._saveMessages(msgs);});}async clear() {return this._enqueue(async () => {this._atomicWrite("[]");});}
}

什么时候做持久化？

不需要每一轮都写磁盘，这样太频繁了：