Standardized API responses for NestJS

• Metadata-based wrapper to provide customizable and standardized API response objects;
• Built-in handling of pagination, sorting and filtering;
• Allows route handlers to keep returning classes instead of wrapper objects, so they remain fully compatible with interceptors;
• Automatic OpenAPI documentation with proper response schema for all features
• Generation of OpenAPI response examples with proper serialization for each user role

Getting started

🚀   Install

$ npm install nest-standard-response

🔮   Add to your app's imports array

app.module.ts

import { StandardResponseModule } from 'nest-standard-response';

@Module({
  imports: [
    StandardResponseModule.forRoot(options), // options can be ommited
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Check out the options that this module accepts in the Advanced Configuration section.

📦   All routes are now wrapped

By default, all routes are automatically wrapped in a standard response object:

// route returns dtos @get("/books") listBooks(): BookDto[] { const books = [ new BookDto({ title: "Dune", year: 1965 }), new BookDto({ title: "Jaws", year: 1974 }), new BookDto({ title: "Emma", year: 1815 }), ]; return books; }

// but response is wrapped { success: true, isArray: true, // auto infered data: [ { title: "Dune", year: 1965 }, { title: "Jaws", year: 1974 }, { title: "Emma", year: 1815 }, ] }

To skip wrapping a particular route, just decorate the handler with @RawResponse().

It's possible to invert this behavior to not wrap any route automatically, and only wrap routes annotated with @StandardResponse() instead. Check out how.

🚦   Wrapping only happens at the end of the NestJS' request pipeline

So interceptors like ClassSerializer and RoleSerializer work transparently without any custom logic.

🔥   Add features to your route

Just decorate a route with @StandardResponse({...options}) and pass in the options you want. Adding features will:

• Automatically prepare a route to receive query parameters for that feature;
• Parse and validate the input of these query parameters, and make them injectable into the handler;
• Add fields to the response object to let the client know the state of these features (and to allow discoverability of defaults when the route is called without any query params);
• Add documentation to Swagger with fully qualified schemas and examples;

To access this information during the request, use the @StandardParam() parameter decorator to inject a params object into your handler. This object contains the parsed query params, all the configuration values you set in the @StandardResponse(), plus methods to manipulate and add data into the response.

// route @get("/books") @StandardResponse({ isPaginated: true }) async listBooks( @StandardParam() params: StandardParams ): BookDto[] { const { books, count } = await this.bookService.list({ // already validated values safe to use limit: params.pagination.limit, offset: params.pagination.offset, }); // add extra information into the response params.setPaginationInfo({ count: count }) return books; }

// response { success: true, isArray: true, isPaginated: true, pagination: { limit: 10, offset: 0, defaultLimit: 10, // 👇 added in handler count: 33 }, data: [ { title: "Dune", year: 1965 }, { title: "Jaws", year: 1974 }, { title: "Emma", year: 1815 }, ] }

🎁   Combine features!

Features can be freely combined, or used all at once.

For example, using the features shown bellow, the route could be called like this:

/books?limit=8&offset=16&sort=-author,title&filter=author^=Frank;year>=1960;year>=1970
Note: This url was NOT url-encoded for readability (but you would need to encode yours)

// route @get("/books") @StandardResponse({ // 👇 declare type to get OpenApi docs type: [BookDto], isPaginated: true, defaultLimit: 12, maxLimit: 20, isSorted: true, sortableFields: ["title", "author"], isFiltered: true, filterableFields: ["author", "year"], }) async listBooks( @StandardParam() params: StandardParams ): BookDto[] { const { books, count } = await this.bookService.list({ limit: params.pagination.limit, offset: params.pagination.offset, sort: params.sorting.sort, filter: params.filtering.filter, }); // 👆 to see how the 'sort' and 'filter' // params are parsed, look at the // SortingInfo and FilteringInfo classes // in the @StandardParam() section of // this document // 👇 add extra information into the response params.setPaginationInfo({ count: count }) params.setMessage('A full-featured example!') return books; }

// response { success: true, message: "A full-featured example!", isArray: true, isPaginated: true, isSorted: true, isFiltered: true, pagination: { query: "limit=8&offset=16", limit: 8, offset: 16, defaultLimit: 12, maxLimit: 20, count: 33 }, sorting: { sortableFields: ["title", "author"], query: "-author,title", sort: [ { field: "author", order: "des" }, { field: "title", order: "asc" } ] }, filtering: { filterableFields: ["author", "year"], query: "author^=Frank;year>=1960;year>=1970", filter: { allOf: [ { anyOf: [ { field: 'author', operation: '^=', value: "Frank" }, ]}, { anyOf: [ { field: 'year', operation: '>=', value: 1960 }, ]}, { anyOf: [ { field: 'year', operation: '<=', value: 1970 }, ]} ] } }, data: [ ... ] }

For detailed information on the objects generated by filtering and sorting, as well as a list of all operations available, see the documentation for the @StandardParam() decorator.

---

Reference

• @StandardResponse() ^decorator
  • StandardResponseOptions
• @RawResponse() ^decorator
• @StandardParam() ^{parameter decorator}
• Advanced Configuration

🟠   @StandardResponse(options?: StandardResponseOptions)

A decorator that wraps the return of a route into a standardized API response object (while still allowing the handler to return true DTOs or other model class instances — this makes interceptors like caching, ClassSerializer, or RoleSerializer work transparently.)

The wrapper allows custom messages to be set in the response, and has optional features to handle common tasks, like pagination, sorting and filtering.

It can also optionally apply swagger's documentation, providing the correct combined schema for the DTO and the wrapper including any of its features. If given an array of Roles, it can also build Swagger route response examples for each user role, containing the reponse as it would be serialized for that user group.

import { UserDto } from './dto/user.dto';

@Controller('users')
export class UsersController {
  constructor(
    private readonly usersService: UsersService,
  ) {}

  @Get('/')
  @StandardResponse({ type: [UserDto] })
  async findAll(): Promise<UserDto[]> {
    const users = await this.usersService.findAll();
    return users // <--- returns an array of UserDtos
  }
}

// get /api/users
// Response:
{
  "success": true,
  "isArray": true,
  "data": [
    Users... // <--- The returned array is delivered inside the data property
  ]
}

(TODO image of swagger UI with the response examples dropdown open. Comparing a response for User and Admin, with arrows showcasing the extra fields returned only to admin)

🔸   StandardResponseOptions

Option	Type	Description
type	Class	The class that represents the object(s) that will be returned from the route (for example, a Model or a DTO). This option is required to get auto-documentation.
description	string	Used as the desciption field of the response in the OpenAPI docs.
isPaginated	boolean	Mark the route to serve paginated responses, and allow the use of pagination options. This will capture and validate limit and offset query parameters, and make them available in the handler via @StandardParam. Also sets up pagination fields in the response object.
isSorted	boolean	Mark the route to serve sorted responses, and allow the use of sorting options. This will capture and validate the sort query parameter, and make it available in the handler via @StandardParam. Also sets up sorting fields in the response object.
isFiltered	boolean	Mark the route to serve filtered responses, and allow the use of filtering options. This will capture and validate the filter query parameter, parse it into a FilteringQuery, an and make it available in the handler via @StandardParam. Also sets up filtering fields in the response object.
defaultLimit	number	(Pagination option) The value to used for limit if the query param is missing. (Defaults to 10)
maxLimit	number	(Pagination option) The maximum value accepted by the limit query param.
minLimit	number	(Pagination option) The minimum value accepted by the limit query param.
sortableFields	string[]	(Sorting option) A list of fields that can used for sorting. If left undefined, all fields will be accepted. An empty array allows no fields.
filterableFields	string[]	(Filtering option) A list of fields that can used for filtering. If left undefined, all fields will be accepted. An empty array allows no fields.

---

🟠   @RawResponse()

The default behavior of StandardResponse is to wrap the response from all routes application wide. This keeps the API consistent and predictable. However, if you need to skip this behavior for a particular route, just set the @RawResponse() decorator:

@Controller('external-api-integration')
export class ExternalApiIntegrationController {
  @Get('/')
  @RawResponse() // <--- will skip wrapping
  async findAll(): Promise<SomeCustomObject> {
    return customObject;
  }
}

If you're adding StandardResponse into an existing app, it might be useful to invert this behavior to create a gradual transition path. To do this, set the interceptAll option to false when importing the StandardResponseModule in your application. This way, routes will only be wrapped if they have explicitly set the @StandardResponse() decorator. See more information in the "Configuring" section bellow.

---

🟠   @StandardParam()

A parameter decorator used to inject a StandardParams object in the route handler.

This object allows access to:

• All options set in @StandardResponse();
• Information captured from query parameters, parsed and validated;
• Methods to include and modify fields in the response object;

import { UserDto } from './dto/user.dto';

@Controller('users')
export class UsersController {
  constructor(
    private readonly usersService: UsersService,
  ) {}

  @Get('/')
  @StandardResponse({
    type: [UserDto],
    isPaginated: true,
    maxLimit: 24,
    defaultLimit 12,
  })
  async findAll(
    @StandardParam() params: StandardParams // <--- inject into handler
  ): Promise<UserDto[]> {
    const [users, count] = await this.usersService.findAll({
      limit: params.pagination.limit,
      offset: params.pagination.offset,
    });
    params.setPaginationInfo({ count: 348 }) // <--- set additional info
    return users;
  }
}

// get /api/users?limit=15&offset=30
// Response:
{
  "success": true,
  "isArray": true,
  "isPaginated": true,
  "pagination: {
    count: 348, // <--- added inside the handler
    limit: 15, // <--- from query
    offset: 30,
    maxLimit: 24, // <--- from decorator options
    defaultLimit: 12,
  }
  "data": [
    Users...
  ]
}

The params object injected with @StandardParam() contains these keys:

Key	Type	Description
pagination	PaginationInfo	Only available when the response isPaginated option is true.
sorting	SortingInfo	Only available when the response isSorted option is true.
filtering	FilteringInfo	Only available when the response isFiltered option is true.
setPaginationInfo()	(info: {}) => void	Allows modifying the pagination metadata inside the route handler to add extra information or to reflect some dynamic condition. For example, to add a pagination count. The object passed to this method will be merged with the current information, so partial updates are OK.
setSortingInfo()	(info: {}) => void	Allows modifying the sorting metadata inside the route handler.
setFilteringInfo()	(info: {}) => void	Allows modifying the filtering metadata inside the route handler.
setMessage()	(message: string) => void	Allows setting a custom message in the response object.

🔸   PaginationInfo

Property	Type	Description
query?	string	The original string from the request for the limit and offset query params. [ReadOnly]
limit?	number	How many items to send. This is the same as the limit query param, but parsed and validated.
offset?	number	How many items to skip. This is the same as the offset query param, but parsed and validated.
count?	number	The total count of items that are being paginated. This value needs to be set inside the handler using the setPaginationInfo() method.
maxLimit?	number	The maximum value accepted by the limit query param. [ReadOnly] (From the options set in @StandardResponse()).
minLimit?	number	The minimum value accepted by the limit query param. [ReadOnly] (From the options set in @StandardResponse()).
defaultLimit?	number	The default number of items to send if no query limit is provided. [ReadOnly] (From the options set in @StandardResponse()).

🔸   SortingInfo

Property	Type	Description
query?	string	The original string from the request for the sort query param.
sortableFields?	string[]	A list of all the fields that can used for sorting. [ReadOnly] (From the options set in @StandardResponse()).
sort?	SortingOperation[]	An array of SortingOperation objects parsed from the query.
SortingOperation
field	string	The name of the field being sorted.
order	'asc' | 'des'	Order of the sorting operation. These strings are available in an enum for static typing: SortingOrder.ASC and SortingOrder.DES.

🔸   FilteringInfo

Property	Type	Description
query?	string	The original string from the request for the filter query param.
filterableFields?	string[]	A list of all the fields that can used for filtering. [ReadOnly] (From the options set in @StandardResponse()).
filter?	{ allOf: FilteringQueryGroup[] }	Filter is an object parsed from the query containing a single property: allOf. This is an array of FilteringQueryGroup objects. All of these filter groups should be combined using an AND operation.
FilteringQueryGroup
anyOf	FilteringQueryOperation[]	An array of FilteringQueryOperation objects. These filters should be combined using an OR operation.
FilteringQueryOperation
field	string	Name of the field to filter on.
operation	string	The comparison operation to perform. Possible operators are bellow.
value	string	Value used for the comparison.

Operation	Description	URL Encoded Form	Example
==	Equals	%3D%3D	.
!=	Not Equals	!%3D	.
<=	Less than or equal to	%3C%3D	.
<	Less than	%3C	.
>=	Greater than or equal to	%3E%3D	.
>	Greater than	%3E	.
=@	Contains	%3D@	.
!@	Does not contain	!@	.
=^	Starts with	%3D%5E	.
=$	Ends with	%3D%24	.

These rules are similar to other APIs like Google Analytics or Matomo Analytics.

🔸   Building the search query

When building a query, all AND operations should be separated by a semicolon (;), and all OR operations should be separed by a comma (,). For example:

This query will filter all books available for lending, which were first published in France OR Italy, between 1970 AND 1999, whose author starts with Vittorio OR ends with Alatri:

available==true;country==France,country==Italy;year>=1970;year<=1999;author=^Vittorio,author=$Alatri

The resulting parsed object from this query will be:

{ allOf: [
  { anyOf: [
    { field: 'available', operation: '==', value: true },
  ]},
  { anyOf: [
    { field: 'country', operation: '==', value: 'France' },
    { field: 'country', operation: '==', value: 'Italy' },
  ]},
  { anyOf: [
    { field: 'year', operation: '>=', value: 1970 },
  ]},
  { anyOf: [
    { field: 'year', operation: '<=', value: 1999 },
  ]},
  { anyOf: [
    { field: 'author', operation: '=^', value: 'Vittorio' },
    { field: 'author', operation: '=$', value: 'Alatri' },
  ]},
]}

---

🟠   Advanced configuration

✅ validateResponse

Allows you to provide a validation function to stop the return of a route if certain conditions are met.

For example: this can abort a request if a route tries to return — instead a DTO — a raw DB document or some other object that may leak information not intended to be exposed.

This function should return false to abort the request.

@Module({
  imports: [
    StandardResponseModule.forRoot({
      validateResponse: (data) => {
        if (isMongooseObject(data)) return false;
        return true;
      },
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

✅ interceptAll

Setting interceptAll to false will invert the default behavior of wrapping all routes by default, and will instead only wrap routes decorated with @StandardResponse().

@Module({
  imports: [
    StandardResponseModule.forRoot({
      interceptAll: false
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

---

🚀   TODO Milestones

• Allow setting any custom field in the repsonse object by exposing a method in the StandardParam: setExtra(field, value);

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