Tutorial: map a user to a DTO

See the repetitive transformation code AutoMapper replaces in a class-based application.

This tutorial maps a database-facing User model to a public UserDto. It uses @automapper/classes, but the same mapping concepts apply to other strategies.

export class User {
  firstName!: string;
  lastName!: string;
  username!: string;
  password!: string;
  bio!: Bio;
}

export class Bio {
  job!: Job;
  birthday!: Date;
  avatarUrl!: string;
}

export class Job {
  title!: string;
  salary!: number;
}

export class UserDto {
  firstName!: string;
  lastName!: string;
  fullName!: string;
  username!: string;
  bio!: BioDto;
}

export class BioDto {
  jobTitle!: string;
  jobSalary!: number;
  birthday!: string;
  avatarUrl!: string;
}

Without a mapping layer, constructors, factories, or services must repeatedly copy matching values, flatten bio.job, format the birthday, and compute fullName. That couples the destination model to its source and spreads transformation rules through the application.

The next steps move those rules into a mapper:

1. Create a mapper and describe model metadata.
2. Create mappings between model identifiers.
3. Configure the differences.
4. Group mappings in profiles.