Commands

When a user needs to input data into the application, they must send this data in the body of a request. This body encapsulates the necessary data to perform an operation. This body is called the command or DTO (Data Transfer Object).

A command in NestJS is a simple class with properties. We use the class-validator package to validate this body. The validation module in the template project validates all body requests by default.

Example

INFO

Don't forget to add @ApiProperty() decorators to generate OpenAPI documentation.

Below is an example of a command to create a new product.

export class CreateProductCommand {
  @ApiProperty({ type: String, example: 'Wise Cookies' })
  @IsString()
  @IsNotEmpty()
  name: string

  @ApiProperty({ type: Number })
  @IsNumber()
  @IsPositive({ message: 'Price must be a positive number' })
  price: number

  @ApiProperty({ type: Number })
  @IsNumber()
  @Min(0, { message: 'Stock must be at least 0' })
  stock: number

  @ApiProperty({ enum: ProductCategory, enumName: 'ProductCategory', required: false })
  @IsOptional()
  @IsEnum(ProductCategory)
  category?: ProductCategory

  @ApiProperty({ type: String, isArray: true })
  @IsArray()
  @IsString({ each: true })
  @ArrayMinSize(1, { message: 'There should be at least 1 tag' })
  tags: string[]
}

If the provided decorators in the class-validator package are not sufficient for your needs, you can always create a custom validator by implementing the ValidatorConstraintInterface interface.

When the command is ready, you can use it in your controller by applying the @Body() decorator before the function parameter.

@Controller('products')
export class CreateProductController {
  @Post()
  async createOne(
    @Body() command: CreateProductCommand
  ) {
    await this.useCase.createProduct(command);
  }
}

INFO

Make sure to import the command without the type prefix.

NestJS will otherwise not be able to validate the command.

✅ import { CreateProductCommand } from './create-product.command';

❌ import type { CreateProductCommand } from './create-product.command.ts';