Validate nested objects using class validator and nestjs

for me, I would able to validate nested object with 'class-transformer'

import { Type } from 'class-transformer';

full example:

import {
  MinLength,
  MaxLength,
  IsNotEmpty,
  ValidateNested,
  IsDefined,
  IsNotEmptyObject,
  IsObject,
  IsString,
} from 'class-validator';
import { Type } from 'class-transformer';

class MultiLanguageDTO {
  @IsString()
  @IsNotEmpty()
  @MinLength(4)
  @MaxLength(40)
  en: string;

  @IsString()
  @IsNotEmpty()
  @MinLength(4)
  @MaxLength(40)
  ar: string;
}

export class VideoDTO {
  @IsDefined()
  @IsNotEmptyObject()
  @IsObject()
  @ValidateNested()
  @Type(() => MultiLanguageDTO)
  name!: MultiLanguageDTO;
}

You are expecting positions: [1] to throw a 400 but instead it is accepted.

According to this Github issue, this seems to be a bug in class-validator. If you pass in a primitive type (boolean, string, number,...) or an array instead of an object, it will accept the input as valid although it shouldn't.

---

I don't see any standard workaround besides creating a custom validation decorator:

import { registerDecorator, ValidationOptions, ValidationArguments } from 'class-validator';

export function IsNonPrimitiveArray(validationOptions?: ValidationOptions) {
  return (object: any, propertyName: string) => {
    registerDecorator({
      name: 'IsNonPrimitiveArray',
      target: object.constructor,
      propertyName,
      constraints: [],
      options: validationOptions,
      validator: {
        validate(value: any, args: ValidationArguments) {
          return Array.isArray(value) && value.reduce((a, b) => a && typeof b === 'object' && !Array.isArray(b), true);
        },
      },
    });
  };
}

and then use it in your dto class:

@ValidateNested({ each: true })
@IsNonPrimitiveArray()
@Type(() => PositionDto)
positions: PositionDto[];