Summary  
This chapter covers defining Data Transfer Object (DTO) classes to specify expected data structures and using decorators to map incoming request payloads to those DTOs, ensuring type safety and consistency.

General domain of usage  
RESTful web APIs


Create a new file in the `src` folder:

```ts id="dtofile"
create-user.dto.ts
```

Add the following code:

```ts id="dto5"
export class CreateUserDto {
  name: string;
  age: number;
}
```

This DTO defines the structure of the data your application expects.

Now use it in your controller:

```ts id="dto6"
import { Controller, Post, Body } from '@nestjs/common';
import { CreateUserDto } from './create-user.dto';

@Controller('users')
export class UsersController {
  @Post()
  createUser(@Body() body: CreateUserDto) {
    return body;
  }
}
```

Here is what is happening:

* `CreateUserDto`: defines required fields;
* `@Body()`: extracts request data;
* `CreateUserDto`: ensures the data follows the defined structure.

Now send a request with data:

```json id="dto7"
{
  "name": "Alice",
  "age": 30
}
```

The controller receives structured data based on the DTO.

Using DTOs keeps your data consistent and avoids repeating type definitions across your application.


Where is a DTO typically used in Nest.js?

Learn how to build structured backend applications with Nest.js. Organize your code using controllers, services, and modules, handle requests and data validation, and create a complete API using a scalable architecture.

Creating and Using DTOs