Node.js 在我的案例中，mongoose架构内部联接没有得到结果

我遵循了许多mongoose的示例，用于使用模式进行内部连接，但没有得到其他表的响应。 我的问题是我的代码中缺少了什么请帮助我

我还想知道课程和科目的成绩

//类主体模型

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema
const classModel  = require('../class/classModel');
const subjectModel  = require('../subject/subjectModel');

var classsubject = new Schema({    
    ClassId: String,
    SubjectId : String,
    IsShow: { type: Boolean, default : true},   
    classmodel: { type: mongoose.Schema.Types.ObjectId, ref: classModel },
    subjectmodel: { type: mongoose.Schema.Types.ObjectId, ref: subjectModel },

});

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema
const classModel  = require('../class/classModel');
const subjectModel  = require('../subject/subjectModel');

var classsubject = new Schema({    
    ClassId: String,
    SubjectId : String,
    IsShow: { type: Boolean, default : true},   
    classmodel: { type: mongoose.Schema.Types.ObjectId, ref: classinfo },
    subjectmodel: { type: mongoose.Schema.Types.ObjectId, ref: subjectModel },

});

//类模型

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema

var classinfo = new Schema({    
    ClassName: String,
    IsShow: { type: Boolean, default : true},   

});


module.exports = mongoose.model('classinfo', classinfo);

//主题模式

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema

var subject = new Schema({    
    SubjectName: String,
    IsShow: Boolean,   

});


module.exports = mongoose.model('subject', subject);

结果

[
        {
            "IsShow": true,
            "_id": "5e1efc0f354849246c472cfe",
            "SubjectId": "5e1da60bf52acb30b87e92c4",
            "ClassId": "5e1ec13ed777bf28d01e2481",          
            "__v": 0
        }]

---

您必须使用模型名，而不是像下面那样在填充中使用文件/对象名

exports.classSubjectList = async (req, res, next) => {
  const obj = await ClassSubject.find().populate('classinfo').exec();
  res.status(200).json({
        success: true,
        response: obj
      });
};

//类主体模型

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema
const classModel  = require('../class/classModel');
const subjectModel  = require('../subject/subjectModel');

var classsubject = new Schema({    
    ClassId: String,
    SubjectId : String,
    IsShow: { type: Boolean, default : true},   
    classmodel: { type: mongoose.Schema.Types.ObjectId, ref: classModel },
    subjectmodel: { type: mongoose.Schema.Types.ObjectId, ref: subjectModel },

});

const mongoose = require('mongoose');
mongoose.Promise = global.Promise 
const Schema = mongoose.Schema
const classModel  = require('../class/classModel');
const subjectModel  = require('../subject/subjectModel');

var classsubject = new Schema({    
    ClassId: String,
    SubjectId : String,
    IsShow: { type: Boolean, default : true},   
    classmodel: { type: mongoose.Schema.Types.ObjectId, ref: classinfo },
    subjectmodel: { type: mongoose.Schema.Types.ObjectId, ref: subjectModel },

});