CODE EXAMPLE FOR JAVASCRIPT

mongoose virtuals

//virtual properties are fields that are not stored in the database
//but are computed from other fields.
//we can use them to add extra fields to our schema

//model/tourModel.js
tourSchema.virtual('durationWeeks').get(function() {
     //we use this.duration because we want to use this in getter
     return this.duration/7
})
const tourSchema= new mongoose.Schema({},{
     toJSON:{virtuals:true}, // in options object we can pass virtuals:true to get virtual properties in json
     toObject:{virtuals:true},
})

//we cann't use virtual properties in our query because they are not stored in the database