How use the $lookup in mongodb and nodejs because mine is empty-CodePudding

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:"[email protected]" 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

CodePudding user response：

Are these two models connected in any way? 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
})

CodePudding user response：

Thanks for your help, It is my update in model

const mongoose = require('mongoose');

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

module.exports = mongoose.model('dataCours', Cours);

And in my $lookup

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

And my data like that in dataCours

id:62ac815300878fa91f1549b9 name_Cours:Array 0:62a33ab745819dea27c8943d date_Commenc:2022-01-12T00:00:00.000 00:00

And in usercng, I have a id

_id:62a33ab745819dea27c8943d

But the result is empty