Populate Models

Populate in mongoose

Situation: In many times, Models need to other model's data.

For example, A 'Book' model needs 'Author' model. In this case we can define author field in Book model. Or we can bring author models using POPULATE method.

If you dont know 'populate' look here "https://mongoosejs.com/docs/populate.html"

How to use populate.

• There is two models : Book, Author

Book ModelSchema

// models/Book.js
var BookSchema = mongoose.Schema({
    title: String,
    pageQunitity: Number,
    publishingCompany: String
}, {
    toJSON: { virtuals: true },        // To show populated data, we need to set thse to options
    toObject: { virtuals: true }    //
});

BookSchema.virtual('author', {
    ref: 'Author',
    localField: '_id',        // this means 'BookSchema._id'
    foreignField: 'book'     // this means 'models/author.js/ AuthorSchema.book'
});

// The ref option, which tells Mongoose which model to populate documents from.
// The localField and foreignField options. Mongoose will populate documents from the model in ref whose foreignField matches this document's localField.

Author ModelSchame

// models/author.js
var AuthorSchema = mongoose.Schema({
    book:{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Book',
        required: true
    },
    name: String,
    age: Number,
});

Adapting populate in query

We just need to put "populate('author')" when we find datas.

const book = await Book.findById(bookId).populate('author');

response

Before using populate.

{
    "success": true,
    "data": {
        "_id": "5f4674264ec3915394fcc374",
        "title": "Real book",
        "pageQunitity": 340,
        "publishingCompany": "acdc",
    }
}

After using populate.

{
    "success": true,
    "data": {
        "_id": "5f4674264ec3915394fcc374",
        "title": "Real book",
        "pageQunitity": 340,
        "publishingCompany": "acdc",
        "author": [                    // WE GOT 'AUTHOR' DATA !
            {
                "_id": "5f489aa99866a05b5016212d",
                "name": "jordan k",
                "age": 20
            }
        ]
    }
}