node.js - 类型错误 : Cannot read property 'belongsTo' of undefined

Question

我正在尝试在 2 个模型“培训师和类(class)”之间建立多对多的关联，因此我使用第三个模型“CourseTrainer”来尝试 1 对多的关系。
但我收到此错误:
C:\Users\DELL\Downloads\graphql-12.18.2020\graphql-12.18.2020\graphql-12.18.2020\serverapp\database\database.js:54
db.trainer.belongsTo(db.tblCourseTrainer, {
^
类型错误:无法读取未定义的属性“belongsTo”
在对象。 (C:\Users\DELL\Downloads\graphql-12.18.2020\graphql-12.18.2020\graphql-12.18.2020\serverapp\database\database.js:54:14)
在 Module._compile (internal/modules/cjs/loader.js:1063:30)
在 Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
在 Module.load (internal/modules/cjs/loader.js:928:32)
在 Function.Module._load (internal/modules/cjs/loader.js:769:14)
在 Module.require (internal/modules/cjs/loader.js:952:19)
在要求 (internal/modules/cjs/helpers.js:88:18)
在对象。 (C:\Users\DELL\Downloads\graphql-12.18.2020\graphql-12.18.2020\graphql-12.18.2020\serverapp\graphql\resolvers\user.js:6:12)
在 Module._compile (internal/modules/cjs/loader.js:1063:30)
在 Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
数据库代码:

const Sequelize = require('sequelize');
const db = {};
const sequelize =  new Sequelize("firstDB"," "," ", {
  //from the DB amazom
  host: '  ',
    dialect: 'mysql',
    define: {
      timestamps: false,
      freezeTableName: true
    },
    operatorsAliases: false,
    pool: {
      max: 5,
      min: 0,
      acquire: 30000,
      idle: 10000
    },
  });

  db.sequelize = sequelize
  db.Sequelize = Sequelize
  db.Sequelize = sequelize
  db.Sequelize = sequelize
  db.Sequelize = sequelize
  db.Sequelize = sequelize
  db.Sequelize = sequelize

  
  db.tblUser = require("./models/user")(sequelize, Sequelize);
  db.vewStudentCourseTrainer = require("./models/studentCourseTrainer")(sequelize, Sequelize);
  db.tblTrainer = require("./models/trainer")(sequelize, Sequelize);
  db.tblCourse = require("./models/course")(sequelize,Sequelize);
  db.tblStudent = require("./models/student")(sequelize,Sequelize);
  db.tblCourseTrainer = require("./models/courseTrainer")(sequelize, Sequelize);
  db.tblStudentCourse = require("./models/studentCourse")(sequelize, Sequelize);

  db.tblCourseTrainer.hasMany(db.tblTrainer, { as: "trainer" });
  db.trainer.belongsTo(db.tblCourseTrainer, {
    foreignKey: "intTrainerID",
    as: "trainerID",
  });

  module.exports = db

CourseTrainer 的模型代码

module.exports = (sequelize,DataTypes)=>{
    const CourseTrainer  = sequelize.define("tblCourseTrainer",{
      intCourseTrainerID: {
        type: DataTypes.INTEGER,
        primaryKey: true,
        autoIncrement: true,
      },             
      intCourseID: {
        type: DataTypes.INTEGER,
        foreignKey: true,
    },
    intTrainerID: {
        type: DataTypes.INTEGER,
        foreignKey: true,
    },
},)
    return CourseTrainer
  }

培训师的型号代码

module.exports = (sequelize,DataTypes)=>{
    const Trainer  = sequelize.define("tblTrainer",{
      intTrainerID: {
        type: DataTypes.INTEGER,
        primaryKey: true,
        autoIncrement: true,
      },             
      strTrainerName: {
        type: DataTypes.STRING
    },
    
    },)
    return Trainer
  }

类(class)模型代码

module.exports = (sequelize,DataTypes)=>{
    const Course  = sequelize.define("tblCourse",{
      intCourseID: {
        type: DataTypes.INTEGER,
        primaryKey: true,
        autoIncrement: true,
      },             
      strCourseName: {
        type: DataTypes.STRING
    },
    },)
    return Course
  }

Answer 1

当你调用这个时:

db.trainer.belongsTo(...)

.trainer 对象中没有 db 对象，因此 db.trainer 是 undefined，您会收到错误消息，告诉您无法访问 .belongsTo() 值上的属性 undefined。
我们可以在这里看到你在哪里声明 db 对象:

const db = {};

并且，然后按照代码一直到您尝试执行 db.trainer.belongsTo(...) 的地方，并且在那里您没有定义 db.trainer 。你有这个:

db.tblTrainer = require("./models/trainer")(sequelize, Sequelize);

所以，也许你打算使用这个？

db.tblTrainer.belongsTo(...)