Create a mapper

Configure the classes strategy and describe class metadata with AutoMap decorators.

Install the packages

npm install @automapper/core @automapper/classes reflect-metadata

pnpm add @automapper/core @automapper/classes reflect-metadata

bun add @automapper/core @automapper/classes reflect-metadata

Enable experimentalDecorators and emitDecoratorMetadata in tsconfig.json, then import reflect-metadata before decorated classes are evaluated.

Create one mapper

import { classes } from '@automapper/classes';
import { createMapper } from '@automapper/core';

export const mapper = createMapper({
  strategyInitializer: classes(),
});

A typical application keeps one mapper per strategy. Mappings registered on that mapper are reused by every map operation.

Describe class metadata

Decorate properties that participate in mapping. Give nested classes an explicit type callback and omit sensitive properties that should not be mapped by convention.

import { AutoMap } from '@automapper/classes';

export class User {
  @AutoMap()
  firstName!: string;

  @AutoMap()
  lastName!: string;

  @AutoMap()
  username!: string;

  password!: string;

  @AutoMap(() => Bio)
  bio!: Bio;
}

export class Bio {
  @AutoMap(() => Job)
  job!: Job;

  @AutoMap()
  birthday!: Date;

  @AutoMap()
  avatarUrl!: string;
}

export class Job {
  @AutoMap()
  title!: string;

  @AutoMap()
  salary!: number;
}

import { AutoMap } from '@automapper/classes';

export class UserDto {
  @AutoMap()
  firstName!: string;

  @AutoMap()
  lastName!: string;

  @AutoMap()
  fullName!: string;

  @AutoMap()
  username!: string;

  @AutoMap(() => BioDto)
  bio!: BioDto;
}

export class BioDto {
  @AutoMap()
  jobTitle!: string;

  @AutoMap()
  jobSalary!: number;

  @AutoMap()
  birthday!: string;

  @AutoMap()
  avatarUrl!: string;
}

The classes strategy can infer primitive design types. Nested models and arrays should use explicit callbacks such as @AutoMap(() => Bio) and @AutoMap(() => [User]).