TypeORM MySQLDataSource未定义问题求助

我用Node.js+Express开发微服务，采用TypeORM搭配MySQL实现数据库映射。严格按照官方文档完成配置后，调试时发现Repository.ts里引用MySQLDataSource会报错，提示ReferenceError: MySQLDataSource is not defined。这是我第一次使用TypeORM，求解决办法。

相关代码 #

data-source.ts #

import "reflect-metadata";
import {DataSource} from 'typeorm';

/**
 * Various data source can be configured here
 */
export const MySQLDataSource = new DataSource({
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "root",
    password: "password",
    database: "ignite_tuition_node_db",
    entities: ["dist/entities/*.js"],
    logging: true,
    synchronize: true,
    entitySkipConstructor: true,
});

index.ts #

import "reflect-metadata";
import express, { Application } from "express";
const expressApp = require('./express-app');

const StartServer = async() => {

    // initialize the application server
    const app: Application = express();
    const PORT = process.env.PORT || 8000;
    
    await expressApp(app);

    // listen to the application server on PORT
    app.listen(PORT, (): void => {
        console.log(`Express application server running on address=> http://localhost:${PORT}`);
    });
}

StartServer();

express-app.ts #

/**
 * Express app
 */
module.exports = async (app: Application) => {

    // initialize mysql datasource
    MySQLDataSource.initialize()
    .then(() => console.log("MySQL Datasource has been successfully initialized"))
    .catch((e) => console.error("Error initializing mysql datasource", e));
    
    // configuring necessary properties for server
    app.use(express.json());

    // controller configuration
    TuitionController(app);
}

Repository.ts #

export function getRepository(entity: any): Repository<any> {
    try {
        return MySQLDataSource.getRepository(entity);
    } catch (e) {
        throw new TuitionServiceException(`Error occurred when finding ${entity} repository`);
    }
}

报错信息 #

MySQLDataSource
Uncaught ReferenceError ReferenceError: MySQLDataSource is not defined
    at eval (repl:1:1)

解决步骤 #

1. 补全缺失的导入语句 #

express-app.ts和Repository.ts都直接使用了MySQLDataSource，但没有从data-source.ts导入该变量，这是报错的核心原因。

• 修改express-app.ts，添加必要导入：

import { Application } from "express";
import { MySQLDataSource } from "./data-source"; // 导入数据源
import { TuitionController } from "./your-tuition-controller-path"; // 同时导入控制器，否则也会报错

注意替换./your-tuition-controller-path为TuitionController实际的文件路径。

• 修改Repository.ts，添加必要导入：

import { Repository } from "typeorm";
import { MySQLDataSource } from "./data-source"; // 导入数据源
import { TuitionServiceException } from "./your-exception-path"; // 导入自定义异常类

2. 统一模块导入规范 #

代码里同时混用了ESModule（import）和CommonJS（module.exports/require），可能导致模块加载异常，建议统一用ESModule：

• 修改express-app.ts的导出方式：

import { Application } from "express";
import { MySQLDataSource } from "./data-source";
import { TuitionController } from "./your-tuition-controller-path";

export default async (app: Application) => {
    app.use(express.json());
    TuitionController(app);
}

• 修改index.ts的导入方式：

import "reflect-metadata";
import express, { Application } from "express";
import expressApp from './express-app'; // 改用ESModule导入

const StartServer = async() => {
    const app: Application = express();
    const PORT = process.env.PORT || 8000;
    
    await expressApp(app);

    app.listen(PORT, () => {
        console.log(`Express application server running on address=> http://localhost:${PORT}`);
    });
}

StartServer();

3. 确保数据源先于业务代码初始化 #

避免在数据源未初始化时调用getRepository，可以把数据源初始化逻辑移到启动入口：

修改index.ts：

import "reflect-metadata";
import express, { Application } from "express";
import expressApp from './express-app';
import { MySQLDataSource } from "./data-source";

const StartServer = async() => {
    // 优先初始化数据源
    try {
        await MySQLDataSource.initialize();
        console.log("MySQL Datasource has been successfully initialized");
    } catch (e) {
        console.error("Error initializing mysql datasource", e);
        process.exit(1); // 初始化失败直接终止进程
    }

    const app: Application = express();
    const PORT = process.env.PORT || 8000;
    
    await expressApp(app);

    app.listen(PORT, () => {
        console.log(`Express application server running on address=> http://localhost:${PORT}`);
    });
}

StartServer();

内容的提问来源于stack exchange，提问作者CleanCodeOnline