NestJS中导入mysql2/promise包失败，调用createConnection报错

问题 #

在NestJS项目中按照Drizzle ORM的MySQL集成指引操作，导入mysql2/promise包时出现异常，实现代码如下：

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";
import * as schema from './schema';

export const DrizzleAsyncProvider = 'drizzleProvider';

export const drizzleProvider = {
  provide: DrizzleAsyncProvider,
  useFactory: async () => {
    console.log(mysql, '<<<');

    const connection = await mysql.createConnection({
      host: 'host',
      user: 'user',
      database: 'database',
      password: 'password'
    });
    const db = drizzle(connection, { schema, mode: 'default' });

    return db;
  },
  exports: [DrizzleAsyncProvider],
}

运行时抛出错误：

[Nest] 16326  - 04/20/2024, 8:31:46 PM     LOG [NestFactory] Starting Nest application...
undefined <<<
[Nest] 16326  - 04/20/2024, 8:31:46 PM   ERROR [ExceptionHandler] Cannot read properties of undefined (reading 'createConnection')
TypeError: Cannot read properties of undefined (reading 'createConnection')

错误显示导入的mysql对象为undefined，无法调用createConnection方法。

解决方案 #

• 重新安装mysql2依赖
  先排查是否依赖安装不完整，执行命令重新安装：

  npm uninstall mysql2 && npm install mysql2
  # 若使用pnpm或yarn，替换为对应包管理器命令
  

• 调整导入语法
  mysql2/promise的导出格式可能和默认导入不兼容，可改用两种方式：

  1. 直接导入createConnection方法：

     import { drizzle } from "drizzle-orm/mysql2";
     import { createConnection } from "mysql2/promise";
     import * as schema from './schema';
     
     // ... useFactory中直接调用
     const connection = await createConnection({ /* 配置项 */ });
     

  2. 使用命名空间导入，并确保TypeScript配置正确：

     import * as mysql from "mysql2/promise";
     

     同时在项目根目录的tsconfig.json中开启ES模块兼容：

     {
       "compilerOptions": {
         "esModuleInterop": true,
         "allowSyntheticDefaultImports": true
       }
     }
     

• 验证NestJS模块配置
  确认drizzleProvider已被添加到对应模块的providers数组中，若需要跨模块复用，需在模块的exports数组中声明DrizzleAsyncProvider。

内容的提问来源于stack exchange，提问作者i474