vehicle.js

var mongoose = require('mongoose');
var Schema   = mongoose.Schema;

var PriceDetailsSchema = new Schema({
  minimum: Number,
  cancellationFee: Number,
  costPerDistance: Number
});

mongoose.model('PriceDetails', PriceDetailsSchema);

var VehicleSchema = new Schema({
  make: String,
  model: String,
  licensePlate: String,
  imageURL: String,
  max_parcel_weight: String,
  max_parcel_size: String,
  priceDetails: {type: Schema.ObjectId, ref: 'PriceDetails', required: true},
  createdAt: Date,
  updatedAt: Date
});

VehicleSchema.pre('save', function(next) {
  var now = new Date();
  this.updatedAt = now;
  if(!this.createdAt) {
    this.createdAt = now;
  }
  next();
});

module.exports = mongoose.model('Vehicle', VehicleSchema);