nested route using @ApiParam, how to use a custom validator in nestjs?

Question

I’m looking for some help about custom validator & custom decorator in Nest.

FIRST CASE : working one

A DTO, with class-validator anotations :

import { IsNotEmpty, IsString } from 'class-validator';
import { IsOwnerExisting } from '../decorators/is-owner-existing.decorator';

export class CreatePollDto {
  @IsNotEmpty()
  @IsString()
  @IsOwnerExisting() // custom decorator, calling custom validator, using a service to check in db
  ownerEmail: string;

  @IsNotEmpty()
  @IsString()
  @NotContains(' ', { message: 'Slug should NOT contain any whitespace.' })
  slug: string;
}

I use it in a controller :

@Controller()
@ApiTags('/polls')
export class PollsController {
  constructor(private readonly pollsService: PollsService) {}

  @Post()
  public async create(@Body() createPollDto: CreatePollDto): Promise<Poll> {
    return await this.pollsService.create(createPollDto);
  }
}

When this endpoint is called, the dto is validating by class-validator, and my custom validator works. If the email doesn’t fit any user in database, a default message is displayed. That is how I understand it.

SECOND CASE : how to make it work ?

Now, I want to do something similar but in a nested route, with an ApiParam. I’d like to check with a custom validator if the param matches some object in database.
In that case, I can’t use a decorator in the dto, because the dto doesn’t handle the "slug" property, it’s a ManyToOne, and the property is on the other side.

// ENTITIES
export class Choice {
  @ManyToOne((type) => Poll)
  poll: Poll;
}

export class Poll {
  @Column({ unique: true })
  slug: string;

  @OneToMany((type) => Choice, (choice) => choice.poll, { cascade: true, eager: true })
  @JoinColumn()
  choices?: Choice[];
}

// DTOs
export class CreateChoiceDto {
  @IsNotEmpty()
  @IsString()
  label: string;

  @IsOptional()
  @IsString()
  imageUrl?: string;
}

export class CreatePollDto {
  @IsNotEmpty()
  @IsString()
  @NotContains(' ', { message: 'Slug should NOT contain any whitespace.' })
  slug: string;

  @IsOptional()
  @IsArray()
  @ValidateNested({ each: true })
  @Type(() => CreateChoiceDto)
  choices: CreateChoiceDto[] = [];
}

So where should I hook my validation ?

I’d like to use some decorator directly in the controller. Maybe it’s not the good place, I don’t know. I could do it in the service too.

@Controller()
@ApiTags('/polls/{slug}/choices')
export class ChoicesController {
  constructor(private readonly choicesService: ChoicesService) {}

  @Post()
  @ApiParam({ name: 'slug', type: String })
  async create(@Param('slug') slug: string, @Body() createChoiceDto: CreateChoiceDto): Promise<Choice> {
    return await this.choicesService.create(slug, createChoiceDto);
  }
}

As in my first case, I’d like to use something like following, but in the create method of the controller.

@ValidatorConstraint({ async: true })
export class IsSlugMatchingAnyExistingPollConstraint implements ValidatorConstraintInterface {
  constructor(@Inject(forwardRef(() => PollsService)) private readonly pollsService: PollsService) {}

  public async validate(slug: string, args: ValidationArguments): Promise<boolean> {
    return (await this.pollsService.findBySlug(slug)) ? true : false;
  }

  public defaultMessage(args: ValidationArguments): string {
    return `No poll exists with this slug : $value. Use an existing slug, or register one.`;
  }
}

Do you understand what I want to do ? Is it feasible ? What is the good way ?

Thanks a lot !

Jackie McDoniel · Accepted Answer · 2020-09-16 13:47:58Z

1

If you're needing to validate the slug with your custom rules you have one of two options

make a custom pipe that doesn't use class-validator and does the validation directly in it.
Use @Param() { slug }: CreatePollDto. This assumes that everything will be sent via URL parameters. You could always make the DTO a simple one such as

export class SlugDto {
  @IsNotEmpty()
  @IsString()
  @NotContains(' ', { message: 'Slug should NOT contain any whitespace.' })
  slug: string;
}

And then use @Param() { slug }: SlugDto, and now Nest will do the validation via the ValidationPipe for you.

answered Sep 16, 2020 at 13:47

Jackie McDoniel

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dev_Fares · Accepted Answer · 2020-09-16 09:52:50Z

0

If it didn't work with you with service try to use

getConnection().createQueryBuilder().select().from().where() I used it in custom decorator to make a isUnique and it works well, but niot with injectable service.

public async validate(slug: string, args: ValidationArguments): Promise<boolean> { return (await getConnection().createQueryBuilder().select(PollsEntityAlias).from(PollsEntity).where('PollsEntity.slug =:slug',{slug}))) ? true : false; }

answered Sep 16, 2020 at 9:52

dev_Fares

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2 Comments

Seraf Over a year ago

I don't think my problem is that. It's not that the validator isn't working, that it isn't validating. I wonder about my understanding of how to use a validator somewhere other than a dto : in a controller or maybe in a service.

Seraf Over a year ago

I’ve added explanations in my question above. However, I’ve figured out there was a bad copy-paste in the slug validator (it was injecting UsersService instead of PollsService). But that doesn’t change my questioning.

Seraf · Accepted Answer · 2020-09-16 15:36:59Z

That’s so greeat! Thanks a lot, it’s working.

I’ve tried something like that, but can’t find the good way.

The deconstructed { slug }: SlugDto, so tricky & clever ! I’ve tried slug : SlugDto, but it couldn’t work, I was like «..hmmm… how to do that… »

Just something else : in the controller method, I was using (as in documentation) @Param('slug'), but with the slugDto, it can’t work. Instead, it must be just @Param().

Finally, my method :

  @Post()
  @ApiParam({ name: 'slug', type: String })
  public async create(@Param() { slug }: SlugDto, @Body() createChoiceDto: CreateChoiceDto): Promise<Choice> {
    return await this.choicesService.create(slug, createChoiceDto);
  }

And the dto :

export class SlugDto {
  @IsNotEmpty()
  @IsString()
  @NotContains(' ', { message: 'Slug should NOT contain any whitespace.' })
  @IsSlugMatchingAnyExistingPoll()
  slug: string;
}

Agus Neira · Accepted Answer · 2022-11-03 15:39:13Z

Personally, I wouldn't register this as a class-validator decorator, because these are beyond the scopes of Nestjs's dependency injection. Getting a grasp of a service/database connection in order to check the existence of a poll would be troublesome and messy from a validator constraint. Instead, I would suggest implementing this as a pipe. If you want to only check if the poll exists, you could do something like:

@Injectable()
export class VerifyPollBySlugPipe implements PipeTransform {
    constructor(@InjectRepository(Poll) private repository: Repository<Poll>) {}

    transform(slug: string, metadata: ArgumentsMetadata): Promise<string> {
        let found: Poll = await repository.findOne({
          where: { slug }
        });
        if (!found) throw new NotFoundException(`No poll with slug ${slug} was found`);
        return slug;
    }
}

But, since you're already fetching the poll entry from the database, maybe you can give it a use in the service, so the same pipe can work to retrieve the entity and throw if not found. I answered a similar question here, you'd just need to add the throwing of the 404 to match your case. Hope it helps, good luck!

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