Serializing

By default, all entities are monkey patched with toObject() and toJSON methods:

export interface AnyEntity<K = number | string> {
  toObject(parent?: AnyEntity, isCollection?: boolean): Record<string, any>;
  toJSON(...args: any[]): Record<string, any>;
  // ...
}

When you serialize your entity via JSON.stringify(entity), its toJSON method will be called automatically. You can provide custom implementation for toJSON, while using toObject for initial serialization:

@Entity()
export class Book {

  // ...

  toJSON(strict = true, strip = ['id', 'email'], ...args: any[]): { [p: string]: any } {
    const o = this.toObject(...args); // do not forget to pass rest params here

    if (strict) {
      strip.forEach(k => delete o[k]);
    }

    return o;
  }

}

Do not forget to pass rest params when calling toObject(...args), otherwise the results might not be stable.

Hidden Properties

If you want to omit some properties from serialized result, you can mark them with hidden flag on @Property() decorator:

@Entity()
export class Book {

  @Property({ hidden: true })
  hiddenField = Date.now();

}

const book = new Book(...);
console.log(book.toObject().hiddenField); // undefined
console.log(book.toJSON().hiddenField); // undefined

Shadow Properties

The opposite situation where you want to define a property that lives only in memory (is not persisted into database) can be solved by defining your property as persist: false. Such property can be assigned via one of Entity.assign(), em.create() and em.merge(). It will be also part of serialized result.

This can be handle when dealing with additional values selected via QueryBuilder or MongoDB's aggregations.

@Entity()
export class Book {

  @Property({ persist: false })
  count?: number;

}

const book = new Book(...);
book.assign({ count: 123 });
console.log(book.toObject().count); // 123
console.log(book.toJSON().count); // 123