Serialization

Serializers provides clean abstraction layer towards data manipulation before sending the actual response. For instance, sensitive data like user's password should be always excluded from the eventual response. Furthermore, certain properties might require additional transformation, let's say, we don't want to send the whole database entity. Instead, we would like to pick only id and name. The rest should be automatically stripped. Unluckily, manually mapping all entities may bring a lot of confusedness.

Overview

In order to provide a straightforward way to carry out these operations, Nest comes with the ClassSerializerInterceptor class. It uses class-transformer package to provide a declarative and extensible way of transforming objects. Basically, the ClassSerializerInterceptor takes the value returned from the method and call classToPlain() function from class-transformer package.

Exclude properties

Let's assume that we want to automatically exclude a password property from the following entity:

import { Exclude } from 'class-transformer';

export class UserEntity {
  id: number;
  firstName: string;
  lastName: string;

  @Exclude()
  password: string;

  constructor(partial: Partial<UserEntity>) {
    Object.assign(this, partial);
  }
}

Then, return the instance of this class directly from the controller's method.

@UseInterceptors(ClassSerializerInterceptor)
@Get()
findOne(): UserEntity {
  return new UserEntity({
    id: 1,
    firstName: 'Kamil',
    lastName: 'Mysliwiec',
    password: 'password',
  });
}

Hint The ClassSerializerInterceptor is imported from @nestjs/common package.

Now, when you call this endpoint, you'll receive a following response:

{
  "id": 1,
  "firstName": "Kamil",
  "lastName": "Mysliwiec"
}

Expose properties

If you want to expose earlier precalculated property, simply use @Expose() decorator.

@Expose()
get fullName(): string {
  return `${this.firstName} ${this.lastName}`;
}

Transform

You can perform additional data transformation using @Transform() decorator. For example, you want to pick a name of the RoleEntity instead of returning the whole object.

@Transform(role => role.name)
role: RoleEntity;

Pass options

The transform options may vary depending on the certain factors. In order to override default settings, use @SerializeOptions() decorator.

@SerializeOptions({
  excludePrefixes: ['_'],
})
@Get()
findOne(): UserEntity {
  return {};
}

Hint The @SerializeOptions() decorator is imported from @nestjs/common package.

These opions will be passed as a second argument of the classToPlain() function.

Websockets & Microservices

All these guidelines cornern both WebSockets as well as microservices, regardless of transport method that is being used.

Learn more

In order to read more about available decorators, options, visit this page.