Populate query in nodejs and mongodb (using mongoose) - node.js

Question

I have 2 collections for product and product price. In product collection there is a field named product_id which is in String and the same field is in productprice collection with the same name as String.
How can I decide Schema for this and how to populate for which product comes with a field as productprice with it?
product fields : _id,Product_id,name
Product price fields :
_id,Product_id,price
where the same value is in Product_id for both the collections.
const productpriceSchema = mongoose.Schema({
Product_id: {
type: mongoose.Schema.ObjectID,
ref: 'Product'
},
price: String
});
const productSchema = mongoose.Schema({
Product_Name: type: String,
User_Object_ID :type: String,
cid :type: String
});
const Product = module.exports = mongoose.model('Product', productSchema);
const Productprice = module.exports = mongoose.model('Product_price', productpriceSchema);
module.exports.productwithprice = function(callback,limit){
Productprice.find({}, callback).populate('Product_id')
}

Answer 1

//Product Schema
//you don't have to give field _id, mongodb will automatically generate it.
const productSchema = new Schema({
Product_Id: String,
name: String
});
const Product = mongoose.model('Product', productSchema);
//Product Price Schema
const productPriceSchema = new Schema({
Product_Id: {
type: Schema.ObjectId,
ref: 'Product'
},
price: String
});
const ProductPrice = mongoose.model('ProductPrice', productPriceSchema)
ProductPrice.find({query})
.populate('Product_Id')
.exec((err, products) => {
//Logic
});

Answer 2

var ProductSchema = new Schema({
name: String,
productId: String
});
var PriceSchema = new Schema({
name: String,
productId: String
});
ProductSchema.virtual('price', {
ref: 'Price', // The model to use
localField: 'productId', // Find price where `localField`
foreignField: 'productId', // is equal to `foreignField`
// If `justOne` is true, 'price' will be a single doc as opposed to
// an array. `justOne` is false by default.
justOne: true
});
var Product = mongoose.model('Product ', ProductSchema);
var Price = mongoose.model('Price ', PriceSchema);
Product.find({}).populate('price').exec(function(error, products) {
/* `products.price` is available now */
});
For detail, please check Populate Virtuals section of Mongoose population.