Sequelize中出现Cannot read properties of undefined (reading 'define')错误求助

场景还原 #

使用Node.js + Express + TypeScript + Sequelize搭建服务时，按以下代码结构组织出现报错：

1. 在server.service.ts中初始化Sequelize实例并通过桶式导出：

// File --> server.service.ts
import { Sequelize } from 'sequelize';

const sequelize: Sequelize = new Sequelize(DB_NAME, DB_USER, DB_PASSWORD, {
  dialect: "mysql",
  host: DB_HOST,
  pool: { idle: 10000, max: 10, min: 0 },
});

export { sequelize };

2. 在models/User.ts中导入该实例定义模型：

import { DataTypes, ModelDefined, Optional } from "sequelize";
import { Role, User as Usr } from "../types";
import { sequelize } from "../services";

type UserOptionalsAttr = Optional<Usr, "id" | "role">;

const User: ModelDefined<Usr, UserOptionalsAttr> = sequelize.define(
  "User",
  {
    email: {
      allowNull: false,
      type: DataTypes.STRING,
      unique: true,
      validate: { isEmail: true },
    },
    id: {
      autoIncrement: true,
      onDelete: "CASCADE",
      onUpdate: "CASCADE",
      primaryKey: true,
      type: DataTypes.INTEGER,
    },
    password: {
      allowNull: false,
      type: DataTypes.STRING,
      validate: { max: 16, min: 3 },
    },
    role: {
      allowNull: false,
      defaultValue: Role.USER,
      type: DataTypes.STRING,
    },
    username: { allowNull: false, type: DataTypes.STRING },
  },
  { tableName: "users", timestamps: true }
);
export { User };

3. 在控制器中使用模型查询时触发错误：

const foundedUser = await User.findOne({
  where: { email },
});

报错信息：Cannot read properties of undefined (reading 'define')

原因分析 #

这是循环依赖/模块加载顺序异常导致的问题。桶式导入（barrel import）会打乱模块加载顺序，当模型文件尝试导入sequelize实例时，server.service.ts可能还未完成实例初始化，导致导入的sequelize为undefined。

解决方案 #

1. 调整模型加载顺序，确保实例先初始化 #

修改server.service.ts，在Sequelize实例完全初始化后再加载所有模型：

// server.service.ts
import { Sequelize } from 'sequelize';

const sequelize: Sequelize = new Sequelize(DB_NAME, DB_USER, DB_PASSWORD, {
  dialect: "mysql",
  host: DB_HOST,
  pool: { idle: 10000, max: 10, min: 0 },
});

// 延迟加载模型，确保实例已就绪
(async () => {
  await import('./models/User');
  // 可添加更多模型导入
})();

export { sequelize };

2. 优化模型桶式导入结构 #

创建models/index.ts作为模型统一出口，确保模型在实例初始化后加载：

// models/index.ts
import { sequelize } from '../services/server.service';
import { User } from './User';

// 确保模型与实例关联完成
export { User };

控制器中从模型统一入口导入：

import { User } from '../models';

// 查询代码保持不变
const foundedUser = await User.findOne({ where: { email } });

3. 检查TypeScript配置 #

确保tsconfig.json的模块配置支持正确的加载顺序：

{
  "compilerOptions": {
    "module": "CommonJS",
    "target": "ES6",
    "esModuleInterop": true,
    "skipLibCheck": true
  }
}

4. 避免直接从服务桶导入实例 #

如果使用了services/index.ts作为桶文件，直接导入具体的server.service.ts而非桶文件，减少加载顺序不确定性：

// models/User.ts
// 替换 import { sequelize } from "../services";
import { sequelize } from "../services/server.service";

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