- 1. API with NestJS #1. Controllers, routing and the module structure
- 2. API with NestJS #2. Setting up a PostgreSQL database with TypeORM
- 3. API with NestJS #3. Authenticating users with bcrypt, Passport, JWT, and cookies
- 4. API with NestJS #4. Error handling and data validation
- 5. API with NestJS #5. Serializing the response with interceptors
- 6. API with NestJS #6. Looking into dependency injection and modules
- 7. API with NestJS #7. Creating relationships with Postgres and TypeORM
- 8. API with NestJS #8. Writing unit tests
- 9. API with NestJS #9. Testing services and controllers with integration tests
- 10. API with NestJS #10. Uploading public files to Amazon S3
- 11. API with NestJS #11. Managing private files with Amazon S3
- 12. API with NestJS #12. Introduction to Elasticsearch
- 13. API with NestJS #13. Implementing refresh tokens using JWT
- 14. API with NestJS #14. Improving performance of our Postgres database with indexes
- 15. API with NestJS #15. Defining transactions with PostgreSQL and TypeORM
- 16. API with NestJS #16. Using the array data type with PostgreSQL and TypeORM
- 17. API with NestJS #17. Offset and keyset pagination with PostgreSQL and TypeORM
- 18. API with NestJS #18. Exploring the idea of microservices
- 19. API with NestJS #19. Using RabbitMQ to communicate with microservices
- 20. API with NestJS #20. Communicating with microservices using the gRPC framework
- 21. API with NestJS #21. An introduction to CQRS
- 22. API with NestJS #22. Storing JSON with PostgreSQL and TypeORM
- 23. API with NestJS #23. Implementing in-memory cache to increase the performance
- 24. API with NestJS #24. Cache with Redis. Running the app in a Node.js cluster
- 25. API with NestJS #25. Sending scheduled emails with cron and Nodemailer
- 26. API with NestJS #26. Real-time chat with WebSockets
- 27. API with NestJS #27. Introduction to GraphQL. Queries, mutations, and authentication
- 28. API with NestJS #28. Dealing in the N + 1 problem in GraphQL
- 29. API with NestJS #29. Real-time updates with GraphQL subscriptions
- 30. API with NestJS #30. Scalar types in GraphQL
- 31. API with NestJS #31. Two-factor authentication
- 32. API with NestJS #32. Introduction to Prisma with PostgreSQL
- 33. API with NestJS #33. Managing PostgreSQL relationships with Prisma
- 34. API with NestJS #34. Handling CPU-intensive tasks with queues
- 35. API with NestJS #35. Using server-side sessions instead of JSON Web Tokens
- 36. API with NestJS #36. Introduction to Stripe with React
- 37. API with NestJS #37. Using Stripe to save credit cards for future use
- 38. API with NestJS #38. Setting up recurring payments via subscriptions with Stripe
- 39. API with NestJS #39. Reacting to Stripe events with webhooks
- 40. API with NestJS #40. Confirming the email address
- 41. API with NestJS #41. Verifying phone numbers and sending SMS messages with Twilio
- 42. API with NestJS #42. Authenticating users with Google
- 43. API with NestJS #43. Introduction to MongoDB
- 44. API with NestJS #44. Implementing relationships with MongoDB
- 45. API with NestJS #45. Virtual properties with MongoDB and Mongoose
- 46. API with NestJS #46. Managing transactions with MongoDB and Mongoose
- 47. API with NestJS #47. Implementing pagination with MongoDB and Mongoose
- 48. API with NestJS #48. Definining indexes with MongoDB and Mongoose
- 49. API with NestJS #49. Updating with PUT and PATCH with MongoDB and Mongoose
- 50. API with NestJS #50. Introduction to logging with the built-in logger and TypeORM
- 51. API with NestJS #51. Health checks with Terminus and Datadog
- 52. API with NestJS #52. Generating documentation with Compodoc and JSDoc
- 53. API with NestJS #53. Implementing soft deletes with PostgreSQL and TypeORM
- 54. API with NestJS #54. Storing files inside a PostgreSQL database
- 55. API with NestJS #55. Uploading files to the server
- 56. API with NestJS #56. Authorization with roles and claims
- 57. API with NestJS #57. Composing classes with the mixin pattern
- 58. API with NestJS #58. Using ETag to implement cache and save bandwidth
- 59. API with NestJS #59. Introduction to a monorepo with Lerna and Yarn workspaces
- 60. API with NestJS #60. The OpenAPI specification and Swagger
- 61. API with NestJS #61. Dealing with circular dependencies
- 62. API with NestJS #62. Introduction to MikroORM with PostgreSQL
- 63. API with NestJS #63. Relationships with PostgreSQL and MikroORM
- 64. API with NestJS #64. Transactions with PostgreSQL and MikroORM
- 65. API with NestJS #65. Implementing soft deletes using MikroORM and filters
- 66. API with NestJS #66. Improving PostgreSQL performance with indexes using MikroORM
Sometimes we need to perform additional operations on the outcoming data. We might not want to expose specific properties or modify the response in some other way. In this article, we look into various solutions NestJS provides us with to change the data we send in the response.
You can find the code from this series in this repository.
Serialization
The first thing to look into is the serialization. It is a process of transforming the response data before returning it to the user.
In the previous parts of this series, we’ve removed the password in the various parts of our API. A better approach would be using the class-transformer.
users/user.entity.ts
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm'; import { Exclude } from 'class-transformer'; @Entity() class User { @PrimaryGeneratedColumn() public id?: number; @Column({ unique: true }) public email: string; @Column() public name: string; @Column() @Exclude() public password: string; } export default User; |
NestJS comes equipped with ClassSerializerInterceptor that uses class-transformer under the hood. To apply the above transformation, we need to use it in our controller:
1 2 3 | @Controller('authentication') @UseInterceptors(ClassSerializerInterceptor) class AuthenticationController |
If we find ourselves adding ClassSerializerInterceptor to a lot of controllers, we can configure it globally instead.
main.ts
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | import { NestFactory, Reflector } from '@nestjs/core'; import { AppModule } from './app.module'; import * as cookieParser from 'cookie-parser'; import { ClassSerializerInterceptor, ValidationPipe } from '@nestjs/common'; async function bootstrap() { const app = await NestFactory.create(AppModule); app.useGlobalPipes(new ValidationPipe()); app.useGlobalInterceptors(new ClassSerializerInterceptor( app.get(Reflector)) ); app.use(cookieParser()); await app.listen(3000); } bootstrap(); |
The ClassSerializerInterceptor needs the Reflector when initializing.
By default, all properties of our entities are exposed. We can change this strategy by providing additional options to the class-transformer. To do so, we need to use the @SerializeOptions() decorator.
1 2 3 4 5 | @Controller('authentication') @SerializeOptions({ strategy: 'excludeAll' }) export class AuthenticationController |
users/user.entity.ts
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm'; import { Expose } from 'class-transformer'; @Entity() class User { @PrimaryGeneratedColumn() public id?: number; @Column({ unique: true }) @Expose() public email: string; @Column() @Expose() public name: string; @Column() public password: string; } export default User; |
The @SerializeOptions() decorator has more options that you might find useful. It matches the options that you can provide for the classToPlain method in the class-transformer.
The class-transformer library has quite a few useful features. Another noteworthy one is the ability to transform values. To demonstrate it, let’s create a nullable column:
1 2 3 4 5 6 7 | @Entity() class Post { // ... @Column({ nullable: true }) public category?: string; } |
Since the category is a nullable column, it is optional, its value is null until we set it. This means sending null values in the response:
The above behavior might be considered undesirable and the most straightforward way to fix it is to use the @Transform decorator. If the value equals null, we don’t want to send in the response.
1 2 3 4 5 6 7 | @Column({ nullable: true }) @Transform(value => { if (value !== null) { return value; } }) public category?: string; |
Issues with using the @Res() decorator
In the previous part of this series, we’ve used the @Res() decorator to access the Express Response object. Thanks to that, we were able to attach cookies to the response.
1 2 3 4 5 6 7 8 9 10 | @HttpCode(200) @UseGuards(LocalAuthenticationGuard) @Post('log-in') async logIn(@Req() request: RequestWithUser, @Res() response: Response) { const {user} = request; const cookie = this.authenticationService.getCookieWithJwtToken(user.id); response.setHeader('Set-Cookie', cookie); user.password = undefined; return response.send(user); } |
Using the @Res() decorator strips us from some advantages of using NestJS. Unfortunately, it interferes with the ClassSerializerInterceptor. To prevent that, we can follow some advice from the creator of NestJS. If we use the request.res object instead of the @Res() decorator, we don’t put NestJS into the express-specific mode.
1 2 3 4 5 6 7 8 9 | @HttpCode(200) @UseGuards(LocalAuthenticationGuard) @Post('log-in') async logIn(@Req() request: RequestWithUser) { const {user} = request; const cookie = this.authenticationService.getCookieWithJwtToken(user.id); request.res.setHeader('Set-Cookie', cookie); return user; } |
The above is a neat little trick that we use to take advantage of the mechanisms built into NestJS while accessing the Response object directly.
Custom interceptors
Above, we use the @Transform decorator to skip a single property if it equals null. Doing so for every nullable property does not seem like a clean approach.
Fortunately, aside from using the ClassSerializerInterceptor, we can create our own interceptors. Interceptors can serve various purposes, and one of them is manipulating the request/response stream.
utils/excludeNull.interceptor.ts
1 2 3 4 5 6 7 8 9 10 11 12 13 | import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common'; import { Observable } from 'rxjs'; import { map } from 'rxjs/operators'; import recursivelyStripNullValues from './recursivelyStripNullValues'; @Injectable() export class ExcludeNullInterceptor implements NestInterceptor { intercept(context: ExecutionContext, next: CallHandler): Observable<any> { return next .handle() .pipe(map(value => recursivelyStripNullValues(value))); } } |
Each interceptor needs to implement the NestInterceptor and, therefore, the intercept method. It takes two arguments:
- ExecutionContext
- it provides information about the current context,
- CallHandler
- it contains the handle method that invokes the route handler and returns an RxJS Observable
The intercept method wraps the request/response stream, and we can add logic both before and after the execution of the route handler. In the above code, we invoke the route handle and modify the response.
Since there are quite a few places in the NestJS framework that make use of RxJS, the official TypeScript starter already contains it.
utils/recursivelyStripNullValues.ts
1 2 3 4 5 6 7 8 9 10 11 12 13 | function recursivelyStripNullValues(value: unknown): unknown { if (Array.isArray(value)) { return value.map(recursivelyStripNullValues); } if (value !== null && typeof value === 'object') { return Object.fromEntries( Object.entries(value).map(([key, value]) => [key, recursivelyStripNullValues(value)]) ); } if (value !== null) { return value; } } |
In the above function, we recursively travel the data structure and preserve values only if they differ from null. It works both for arrays and plain objects.
If you want to know more about recursion in JavaScript, check out Using recursion to traverse data structures. Execution context and the call stack
Also, every recursive function can be turned into an iterative one
Summary
In this article, we’ve looked into how we can modify the response that we send back to our users. While the most straightforward way to do so is to serialize the response with ClassSerializerInterceptor, we can also create our own interceptor. We’ve also looked into how we can bypass the issue of using the @Res() decorator.