import * as mongoose from 'mongoose'; import { Typegoose, prop, pre } from '../../typegoose'; @pre('save', function(next) { if (this.model === 'Trabant') { this.isSedan = true; } next(); }) export class Car extends Typegoose { @prop({ required: true }) model: string; @prop() isSedan?: boolean; } export const model = new Car().getModelForClass(Car);