validate nested objects using class-validator in nest.js controller

Question

I want to validate body payload using class-validator in a nest.js controller. My currency.dto.ts file is like this:

import {
  IsNotEmpty,
  IsString,
  ValidateNested,
  IsNumber,
  IsDefined,
} from 'class-validator';

class Data {

  @IsNotEmpty()
  @IsString()
  type: string;

  @IsNotEmpty()
  @IsNumber()
  id: number;
}

export class CurrencyDTO {
  @ValidateNested({ each: true })
  @IsDefined()
  data: Data[];
}

and in my nest.js controller, I use it like this.

  @Post()
  @UseGuards(new AuthTokenGuard())
  @UsePipes(new ValidationPipe())
  addNewCurrency(@Req() req, @Body() data: CurrencyDTO) {
    console.log('data', data);
  }

my validation pipe class is like this:

import {
  PipeTransform,
  Injectable,
  ArgumentMetadata,
  BadRequestException,
  HttpException,
  HttpStatus,
} from '@nestjs/common';
import { validate, IsInstance } from 'class-validator';
import { plainToClass, Exclude } from 'class-transformer';

@Injectable()
export class ValidationPipe implements PipeTransform<any> {
  async transform(value: any, metadata: ArgumentMetadata) {
    if (value instanceof Object && this.isEmpty(value)) {
      throw new HttpException(
        `Validation failed: No Body provided`,
        HttpStatus.BAD_REQUEST,
      );
    }
    const { metatype } = metadata;
    if (!metatype || !this.toValidate(metatype)) {
      return value;
    }
    const object = plainToClass(metatype, value);
    const errorsList = await validate(object);
    if (errorsList.length > 0) {
      const errors = [];
      for (const error of errorsList) {
        const errorsObject = error.constraints;
        const { isNotEmpty } = errorsObject;
        if (isNotEmpty) {
          const parameter = isNotEmpty.split(' ')[0];
          errors.push({
            title: `The ${parameter} parameter is required.`,
            parameter: `${parameter}`,
          });
        }
      }
      if (errors.length > 0) {
        throw new HttpException({ errors }, HttpStatus.BAD_REQUEST);
      }
    }
    return value;
  }

  private toValidate(metatype): boolean {
    const types = [String, Boolean, Number, Array, Object];
    return !types.find(type => metatype === type);
  }
  private isEmpty(value: any) {
    if (Object.keys(value).length > 0) {
      return false;
    }
    return true;
  }
}

This validation pipe works fine for all except for nested objects. Any idea what am I doing wrong here? My body payload is like this:

{
"data": [{
    "id": 1,
    "type": "a"
}]
}

Kim Kern · Accepted Answer · 2019-10-17 23:27:09Z

102

Try specifying the nested type with @Type:

import { Type } from 'class-transformer';

export class CurrencyDTO {
  @ValidateNested({ each: true })
  @Type(() => Data)
  data: Data[];
}

For a nested type to be validated, it needs to be an instance of a class not just a plain data object. With the @Type decorator you tell class-transformer to instantiate a class for the given property when plainToClass is called in your VaildationPipe.

If you are using the built-in ValidationPipe make sure you have set the option transform: true.

edited Oct 17, 2019 at 23:27

answered Dec 8, 2018 at 17:23

Kim Kern

61.1k20 gold badges221 silver badges215 bronze badges

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8 Comments

Leonardo Emilio Dominguez Over a year ago

For any reason this solution isn't working for me. I did what you said and it didn't work.

Kim Kern Over a year ago

I have tried it and it works for me. :-/ Without more specific information, I can't help you. Maybe open a new question and add your code?! I'll have a look at it.

Leonardo Emilio Dominguez Over a year ago

I just opened a new post, I will appreciate it if you can give it a look.

mauron85 Over a year ago

I would add. That class-validator does not require this \@Type annotation. It's just how nestjs works. It always uses class-transformer on your DTO and class-transformer requires that \@Type annotation.

RollerCosta Over a year ago

@LeonardoEmilioDominguez try to put both the classes in the same file and make sure nested class appears first(should be at the top), order matters. As you can see Data appears before DataDTO in the question.

|

Xen_mar · Accepted Answer · 2021-11-25 06:49:45Z

11

At least in my case, the accepted answer needed some more info. As is, the validation will not run if the key data does not exist on the request. To get full validation try:

@IsDefined()
@IsNotEmptyObject()
@ValidateNested()
@Type(() => CreateOrganizationDto)
@ApiProperty()
organization: CreateOrganizationDto;

answered Nov 25, 2021 at 6:49

Xen_mar

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Comments

flav1o · Accepted Answer · 2025-02-01 19:30:56Z

1

A bit late to the party but... You can follow the approach from this answer and it will work as expected. I made a custom decorator so that it's possible to use only one line of code instead of two when validating the object:

export function ValidateNestedType(type: () => any) {
  return function (target: object, propertyName: string) {
    ValidateNested({ each: true })(target, propertyName);
    Type(type)(target, propertyName);
  };
}

the usage looks like this:

@InputType()
export class CreateProductInput {
  @ValidateNestedType(() => ProductDetailsInput)
  product: ProductDetailsInput;
  
  ...
}

answered Feb 1 at 19:30

flav1o

436 bronze badges

1 Comment

rtlayzell Apr 21 at 16:45

This worked for me, cheers

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