Calculate custom property based on populate element - node.js

Question

I have two Schemas : recipe and product
var recipeSchema = new mongoose.Schema({
name: {
type: String,
required: true
},
products: [{
product: { type: mongoose.Schema.Types.ObjectId, ref: 'Product' },
productWeight: Number,
productPrice: Number
}]
})
var productSchema = new mongoose.Schema({
name: {
type: String,
required: true
},
weight: {
type: Number,
required: true
},
price: {
type: Number,
required: true
}
})
And I have addRecipe function
module.exports.addRecipe = function(req, res){
Recipe
.create({
name: req.body.name,
products: req.body.products
}, function(err, recipe){
if(err){
console.log("Error creating recipe");
res
.status(400)
.json(err);
} else {
console.log("Recipe created", recipe);
res
.status(201)
.json(recipe);
}
})
}
I'd like to calculate productPrice for every object in array (productPrice = product.price * productWeight / product.Weight).
My posted JSON.
{
"name": "Cake",
"products": [
{
"product": "59728a3f7765441b503e31bc",
"productWeight": 100
},
{
"product": "59728a3f7765441b503e31bd",
"productWeight": 200
},
{
"product": "59728a3f7765441b503e31be",
"productWeight": 50
},
{
"product": "59728a3f7765441b503e31bf",
"productWeight": 500
}
]
}
I'd like also update productPrice on product or reicpe edit.
Is it possible to do this?
Thanks!

Answer 1

I would use a virtual for this, but I don't think it is possible to use it without introducing another schema.
var RecipeProductSchema = new mongoose.Schema({
product: { type: mongoose.Schema.Types.ObjectId, ref: 'Product' },
productWeight: Number
});
// note: product must be populated before calling this property
RecipeProductSchema.virtual('productPrice').get(function() {
return this.product.price * this.productWeight / this.product.weight;
});
var RecipeSchema = new mongoose.Schema({
name: {
type: String,
required: true
},
products: [RecipeProductSchema]
})