如何在 mongodb 和 nodejs 中使用 $lookup，因为我的是空的

Question

I am looking for a way to search for data that has a foreign key. But I haven't found it yet. I've been stuck here for a day. Here is my model

 const mongoose = require('mongoose'); const UserCGN = mongoose.Schema({ username: String, cours: String }) module.exports = mongoose.model('UserCGN', UserCGN); const mongoose = require('mongoose'); const Cours = mongoose.Schema({ name_Cours: String, date_Commenc: Date }) module.exports = mongoose.model('dataCours', Cours);

And I have a data in my database like it

dans UserCGN

username:"njatotianafiononana@gmail.com" cours:"Anglais"

et dans le dataCours

name_Cours:"Anglais" date_Commenc:2022-01-12T00:00:00.000+00:00

Et voici mon code pour récuperer

 var coursM = await CoursModel.aggregate( [ { $lookup: { from: "CGNModel", localField: "name_Cours", foreignField: "cours", as: "inventory_docs" } } ] ) console.log("coursM", coursM);

In my table inventory_docs is always empty. Please, help me

Answer 1

These two models should be connected. From the snippet you provided, it looks like you forgot to do it, and the model should loke something like this. This way you could do lookup with foreignField: "_id"

const Cours = mongoose.Schema({
    name_Cours: [
      { 
         type: mongoose.Schema.Types.ObjectId,
         ref: 'UserCGN',            
      }
    ],
    date_Commenc: Date
})