Operations

In OpenAPI terms, paths are endpoints (resources), such as /users or /reports/summary, that your API exposes, and operations are the HTTP methods used to manipulate these paths, such as GET, POST or DELETE.

Tags

To attach a controller to a specific tag, use the @ApiTags(...tags) decorator.

@ApiTags('cats')
@Controller('cats')
export class CatsController {}

Headers

To define custom headers that are expected as part of the request, use @ApiHeader().

@ApiHeader({
  name: 'X-MyHeader',
  description: 'Custom header',
})
@Controller('cats')
export class CatsController {}

Responses

To define a custom HTTP response, use the @ApiResponse() decorator.

@Post()
@ApiResponse({ status: 201, description: 'The record has been successfully created.'})
@ApiResponse({ status: 403, description: 'Forbidden.'})
async create(@Body() createCatDto: CreateCatDto) {
  this.catsService.create(createCatDto);
}

Nest provides a set of short-hand API response decorators that inherit from the @ApiResponse decorator:

• @ApiOkResponse()
• @ApiCreatedResponse()
• @ApiAcceptedResponse()
• @ApiNoContentResponse()
• @ApiMovedPermanentlyResponse()
• @ApiBadRequestResponse()
• @ApiUnauthorizedResponse()
• @ApiNotFoundResponse()
• @ApiForbiddenResponse()
• @ApiMethodNotAllowedResponse()
• @ApiNotAcceptableResponse()
• @ApiRequestTimeoutResponse()
• @ApiConflictResponse()
• @ApiTooManyRequestsResponse()
• @ApiGoneResponse()
• @ApiPayloadTooLargeResponse()
• @ApiUnsupportedMediaTypeResponse()
• @ApiUnprocessableEntityResponse()
• @ApiInternalServerErrorResponse()
• @ApiNotImplementedResponse()
• @ApiBadGatewayResponse()
• @ApiServiceUnavailableResponse()
• @ApiGatewayTimeoutResponse()
• @ApiDefaultResponse()

@Post()
@ApiCreatedResponse({ description: 'The record has been successfully created.'})
@ApiForbiddenResponse({ description: 'Forbidden.'})
async create(@Body() createCatDto: CreateCatDto) {
  this.catsService.create(createCatDto);
}

To specify a return model for a request, we must create a class and annotate all properties with the @ApiProperty() decorator.

export class Cat {
  @ApiProperty()
  id: number;

  @ApiProperty()
  name: string;

  @ApiProperty()
  age: number;

  @ApiProperty()
  breed: string;
}

Then the Cat model can be used in combination with the type property of the response decorator.

@ApiTags('cats')
@Controller('cats')
export class CatsController {
  @Post()
  @ApiCreatedResponse({
    description: 'The record has been successfully created.',
    type: Cat,
  })
  async create(@Body() createCatDto: CreateCatDto): Promise<Cat> {
    return this.catsService.create(createCatDto);
  }
}

Let's open the browser and verify the generated Cat model:

File upload

You can enable file upload for a specific method with the @ApiBody decorator together with @ApiConsumes(). Here's a full example using the File Upload technique:

@UseInterceptors(FileInterceptor('file'))
@ApiConsumes('multipart/form-data')
@ApiBody({
  description: 'List of cats',
  type: FileUploadDto,
})
uploadFile(@UploadedFile() file) {}

Where FileUploadDto is defined as follows:

class FileUploadDto {
  @ApiProperty({ type: 'string', format: 'binary' })
  file: any;
}

To handle multiple files uploading, you can define FilesUploadDto as follows:

class FilesUploadDto {
  @ApiProperty({ type: 'array', items: { type: 'string', format: 'binary' } })
  files: any[];
}

Extensions

To add an Extension to a request use the @ApiExtension() decorator. The extension name must be prefixed with x-.

@ApiExtension('x-foo', { hello: 'world' })

Advanced: Generic ApiResponse

With the ability to provide Raw Definitions, we can define Generic schema for Swagger UI. Assume we have the following DTO:

export class PaginatedDto<TData> {
  @ApiProperty()
  total: number;

  @ApiProperty()
  limit: number;

  @ApiProperty()
  offset: number;

  results: TData[];
}

We skip decorating results as we will be providing a raw definition for it later. Now, let's define another DTO and name it, for example, CatDto, as follows:

export class CatDto {
  @ApiProperty()
  name: string;

  @ApiProperty()
  age: number;

  @ApiProperty()
  breed: string;
}

With this in place, we can define a PaginatedDto<CatDto> response, as follows:

@ApiOkResponse({
  schema: {
    allOf: [
      { $ref: getSchemaPath(PaginatedDto) },
      {
        properties: {
          results: {
            type: 'array',
            items: { $ref: getSchemaPath(CatDto) },
          },
        },
      },
    ],
  },
})
async findAll(): Promise<PaginatedDto<CatDto>> {}

In this example, we specify that the response will have allOf PaginatedDto and the results property will be of type Array<CatDto>.

• getSchemaPath() function that returns the OpenAPI Schema path from within the OpenAPI Spec File for a given model.
• allOf is a concept that OAS 3 provides to cover various Inheritance related use-cases.

Lastly, since PaginatedDto is not directly referenced by any controller, the SwaggerModule will not be able to generate a corresponding model definition just yet. In this case, we must add it as an Extra Model. For example, we can use the @ApiExtraModels() decorator on the controller level, as follows:

@Controller('cats')
@ApiExtraModels(PaginatedDto)
export class CatsController {}

If you run Swagger now, the generated swagger.json for this specific endpoint should have the following response defined:

"responses": {
  "200": {
    "description": "",
    "content": {
      "application/json": {
        "schema": {
          "allOf": [
            {
              "$ref": "#/components/schemas/PaginatedDto"
            },
            {
              "properties": {
                "results": {
                  "$ref": "#/components/schemas/CatDto"
                }
              }
            }
          ]
        }
      }
    }
  }
}

To make it reusable, we can create a custom decorator for PaginatedDto, as follows:

export const ApiPaginatedResponse = <TModel extends Type<any>>(
  model: TModel,
) => {
  return applyDecorators(
    ApiOkResponse({
      schema: {
        allOf: [
          { $ref: getSchemaPath(PaginatedDto) },
          {
            properties: {
              results: {
                type: 'array',
                items: { $ref: getSchemaPath(model) },
              },
            },
          },
        ],
      },
    }),
  );
};

info Hint Type<any> interface and applyDecorators function are imported from the @nestjs/common package.

With this in place, we can use the custom @ApiPaginatedResponse() decorator on our endpoint:

@ApiPaginatedResponse(CatDto)
async findAll(): Promise<PaginatedDto<CatDto>> {}

For client generation tools, this approach poses an ambiguity in how the PaginatedResponse<TModel> is being generated for the client. The following snippet is an example of a client generator result for the above GET / endpoint.

// Angular
findAll(): Observable<{ total: number, limit: number, offset: number, results: CatDto[] }>

As you can see, the Return Type here is ambiguous. To workaround this issue, you can add a title property to the schema for ApiPaginatedResponse:

export const ApiPaginatedResponse = <TModel extends Type<any>>(model: TModel) => {
  return applyDecorators(
    ApiOkResponse({
      schema: {
        title: `PaginatedResponseOf${model.name}`
        allOf: [
          // ...
        ],
      },
    }),
  );
};

Now the result of the client generator tool will become:

// Angular
findAll(): Observable<PaginatedResponseOfCatDto>