Decorator to return a 404 in a Nest controller

Question

I'm working on a backend using NestJS, (which is amazing btw). I have a 'standard get a single instance of an entity situation' similar to this example below.

@Controller('user') export class UserController {     constructor(private readonly userService: UserService) {}     ..     ..     ..     @Get(':id')     async findOneById(@Param() params): Promise<User> {         return userService.findOneById(params.id);     } 

This is incredibly simple and works - however, if the user does not exist, the service returns undefined and the controller returns a 200 status code and an empty response.

In order to make the controller return a 404, I came up with the following:

    @Get(':id')     async findOneById(@Res() res, @Param() params): Promise<User> {         const user: User = await this.userService.findOneById(params.id);         if (user === undefined) {             res.status(HttpStatus.NOT_FOUND).send();         }         else {             res.status(HttpStatus.OK).json(user).send();         }     }     ..     .. 

This works, but is a lot more code-y (yes it can be refactored).

This could really use a decorator to handle this situation:

    @Get(':id')     @OnUndefined(404)     async findOneById(@Param() params): Promise<User> {         return userService.findOneById(params.id);     } 

Anyone aware of a decorator that does this, or a better solution than the one above?

Answer 1

The shortest way to do this would be

@Get(':id') async findOneById(@Param() params): Promise<User> {     const user: User = await this.userService.findOneById(params.id);     if (user === undefined) {         throw new BadRequestException('Invalid user');     }     return user; } 

There is no point in decorator here because it would have the same code.

Note: BadRequestException is imported from @nestjs/common;

Edit

After some time with, I came with another solution, which is a decorator in the DTO:

import { registerDecorator, ValidationArguments, ValidationOptions, ValidatorConstraint } from 'class-validator'; import { createQueryBuilder } from 'typeorm';  @ValidatorConstraint({ async: true }) export class IsValidIdConstraint {      validate(id: number, args: ValidationArguments) {         const tableName = args.constraints[0];         return createQueryBuilder(tableName)             .where({ id })             .getOne()             .then(record => {                 return record ? true : false;             });     } }  export function IsValidId(tableName: string, validationOptions?: ValidationOptions) {     return (object, propertyName: string) => {         registerDecorator({             target: object.constructor,             propertyName,             options: validationOptions,             constraints: [tableName],             validator: IsValidIdConstraint,         });     }; }  

Then in your DTO:

export class GetUserParams {     @IsValidId('user', { message: 'Invalid User' })     id: number; } 

Hope it helps someone.