开发者问题收集

类型错误：无法读取未定义的属性“belongsTo”

2020-12-29
4612
node.js graphql sequelize.js

我尝试在两个模型“Trainer 和 Course”之间建立多对多关联，因此我创建了第三个模型“CourseTrainer”来尝试建立一对多关系。 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, { ^

TypeError：无法读取未定义的属性“belongsTo” at Object。 (C:\Users\DELL\Downloads\graphql-12.18.2020\graphql-12.18.2020\graphql-12.18.2020\serverapp\database\database.js:54:14) at Module._compile (internal/modules/cjs/loader.js:1063:30) at 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 require (internal/modules/cjs/helpers.js:88:18) 在 Object. (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) 位于 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
  }

Trainer 的模型代码 

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

Course 的模型代码 

module.exports = (sequelize,DataTypes)=>{
    const Course  = sequelize.define("tblCourse",{
      intCourseID: {
        type: DataTypes.INTEGER,
        primaryKey: true,
        autoIncrement: true,
      },             
      strCourseName: {
        type: DataTypes.STRING
    },
    },)
    return Course
  }
2个回答

对我来说，问题在于我在不同的文件中定义了 belongsTo 关联。

解决方案是将关联移动到执行查询的同一文件中。例如 

Grid.belongsToMany(Link, { through: GridLink, foreignKey: 'gridId'})
Link.belongsToMany(Grid, { through: GridLink, foreignKey: 'linkId'})

exports.listLinksInGrid = (gridId) => {
  return Grid.findOne({
    where: {
      id: gridId
    },
    include: Link
  });
};

而不是 

Grid.belongsToMany(Link, { through: GridLink, foreignKey: 'gridId'})

exports.listLinksInGrid = (gridId) => {
  return Grid.findOne({
    where: {
      id: gridId
    },
    include: Link
  });
};

Link.belongsToMany(Grid, { through: GridLink, foreignKey: 'linkId'})
Reese James Wahlin
2022-06-05

当您调用此方法时： 

db.trainer.belongsTo(...)

db 对象中没有 .trainer 对象，因此 db.trainer 为 undefined ，并且您会收到错误消息，告诉您无法访问 undefined 值上的属性 .belongsTo() 。

我们可以在此处看到您声明 db 对象的位置： 

const db = {};

然后，沿着代码往下找到您尝试执行 db.trainer.belongsTo(...) 的位置，但其中没有定义 db.trainer 。您确实有这个： 

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

那么，也许您打算使用它？ 

db.tblTrainer.belongsTo(...)
jfriend00
2020-12-29