How to populate in 3 collection in mongoDB with Mongoose - node.js

Question

I have three collections such as User, Program, and `Agenda. Those models as follows.
User Model
const mongoose = require('mongoose');
const UserSchema = mongoose.Schema({
name: {type:String},
email: {type:String}
},{timestamps:true
}
);
module.exports = mongoose.model('User', UserSchema);
Program Model
const mongoose = require('mongoose');
const NoteSchema = mongoose.Schema({
name: {type:String},
timefrom: {type:Date},
timeto: {type:Date},
status: {type:String},
venue: {type:String},
timetype: {type:Number},
userid:{type:mongoose.Schema.Types.ObjectId,ref : 'User', required: true},
logo :{type:String,default: 'programe'}
},{timestamps:true
});
module.exports = mongoose.model('Program', NoteSchema);
Agenda Model
const mongoose = require('mongoose');
const AgendaSchema = mongoose.Schema({
name: {type:String},
timefrom: {type:Date},
timeto: {type:Date},
status: {type:String},
proorder: {type:String},
proid:{type:mongoose.Schema.Types.ObjectId,ref : 'Program', required: true}
},
{timestamps:true}
);
module.exports = mongoose.model('Agenda', AgendaSchema);
Now I only get agenda and program data only.
Agenda Controller
// Retrieve and return all agenda from the database.
exports.findAll = (req, res) => {
Agenda.find()
.populate('proid')
//.populate('userid')
.then(agendas => {
res.send(agendas);
}).catch(err => {
res.status(500).send({
message: err.message || "Some error occurred while retrieving agenda."
});
});
};
When I go to this URL and GET method I want to populate agenda document(done), related program document(done) and related user document(this I want)?
The wanted query as like this
SELECT *
FROM users, programs, agendas
WHERE agendas.proid = programs.id AND programs.userid = users.id

Answer 1

You can either use $lookup aggregation
Agenda.aggregate([
{ "$lookup": {
"from": Program.collection.name,
"let": { "proid": "$proid" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$proid" ] } } },
{ "$lookup": {
"from": User.collection.name,
"let": { "userid": "$userid" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$userid" ] } } },
],
"as": "userid"
}},
{ "$unwind": "$userid" }
],
"as": "proid"
}},
{ "$unwind": "$proid" }
])
Or with populate
Agenda.find()
.populate([{ path: 'proid', populate: { path: 'userid' }}])
Both will give you the same result

Answer 2

You can use .populate() and { populate : { path : 'field' } }.
Example:
Agenda.find(). //Collection 1
populate({path:'proid', //Collection 2
populate:{path:'userid' //Collection 3
}})
.exec();
After the 4 collection, you need to identify the model, if it can't be wrong
Example:
Agenda.find(). //Collection 1
populate({path:'proid', //Collection 2
populate:{path:'userid', //Collection 3
populate:{path:'otherFiel', model: Collection //Collection 4 and more
}}})
.exec();
And to finish, if you want get only some fields of some Collection, you can use the propiertie select
Example:
Agenda.find().
populate({path:'proid', select:'name status venue'
populate:{path:'userid'
}})
.exec();