Populating Mongoose objects from id to new field

Question

I was working with mongoose to populate field of ids with their respective documents to a new field.my question is assuming my cart model is -

let CartSchema = new mongoose.Schema({
    userId: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User'
    },
    productIds: [
        {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'Product'
        }
    ]
});

i want to populate the products so i used

Cart.find({}).populate("products").exec(function (err, cart) {
    console.log(cart)
}

but this populates the documents in the same field name productIds and i want to populate those fields in a new field name called "products" so i tried this

let CartSchema = new mongoose.Schema({
        userId: {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'User'
        },
        productIds: [
            {
                type: String
            }
        ]
    }, { toJSON: { virtuals: true } });

CartSchema.virtual('products', {
    ref: 'Product',
    localField: 'productIds',
    foreignField: '_id',
});

Cart.find({}).populate("products").exec(function (err, cart) {
    console.log(cart)
}

but returned empty array named products.so how can i populate the productIds array to a new field name products with their respective document array.

Thanks.

Answer 1

There's a way to do this - it's called Virtuals (see docs). The idea is to create a "virtual property" which is not actually saved to the DB and acts as a computed property. As per the example provided by qinshenxue on the related github issue:

// declare your ID field as a regular string
var countrySchema = new mongoose.Schema({
    capitalId: {type:String}
});

// create a virtual field which links between the field you've just declared 
// and the related collection. 
// localField is the name of the connecting field, 
// foreign field is a corresponding field in the connected collection
// justOne says that it'll populate a single connected object, 
// set it to false if you need to get an array
countrySchema.virtual('capital',{
    ref: 'City',
    localField: 'capitalId',
    foreignField: '_id',
    justOne: true
});

// tell Mongoose to retreive the virtual fields
countrySchema.set('toObject', { virtuals: true });
countrySchema.set('toJSON', { virtuals: true });

// now you can populate your virtual field like it actually exists
// the following will return a Country object in the 'capital' field
Country.find().populate('capital') 

Answer 2

the approch is correct you should see your data poulated in the products field. make sure you have the correct data and model n