title: (node:3341) DeprecationWarning: Mongoose: mpromise
body: <p>I'm trying to develop a class on the top of the mongoose with my custom methods, so I extended the mongoose with my own class but when I invoke to create a new car method it works but its strip and error, here I let you see what I'm trying to do.</p>
  
  <p>I'm getting this warning</p>
  
  <pre><code>(node:3341) DeprecationWarning: Mongoose: mpromise (mongoose's default promise library) is deprecated, plug in your own promise library instead: http://mongoosejs.com/docs/promises.html
  </code></pre>
  
  <p>after I do</p>
  
  <pre><code>driver.createCar({
        carName: 'jeep',
        availableSeats: 4,
      }, callback);
  </code></pre>
  
  <p>driver is an instance of Driver class</p>
  
  <pre><code>const carSchema = new Schema({
    carName: String,
    availableSeats: Number,
    createdOn: { type: Date, default: Date.now },
  });
  const driverSchema = new Schema({
   email: String,
   name: String,
   city: String,
   phoneNumber: String,
   cars: [carSchema],
   userId: {
     type: Schema.Types.ObjectId,
     required: true,
   },
  createdOn: { type: Date, default: Date.now },
  });
  const DriverModel = mongoose.model('Driver', driverSchema);
  
  class Driver extends DriverModel {
    getCurrentDate() {
    return moment().format();
  }
  create(cb) {
    // save driver
    this.createdOn = this.getCurrentDate();
    this.save(cb);
  }
  remove(cb) {
    super.remove({
    _id: this._id,
   }, cb);
  }
  createCar(carData, cb) {
    this.cars.push(carData);
    this.save(cb);
  }
  getCars() {
    return this.cars;
   }
  }
  </code></pre>
  
  <p>any thoughts about what Im doing wrong?</p>