如何为 NestJS 上的嵌套验证错误返回干净的消息

Question

I have a nested form validation on my nestjs application, that returns the following result when a field has some error:

Current error message: "products.0.amount A quantidade do produto é obrigatória"

Expected error message: "A quantidade do produto é obrigatória"

For those examples above, I have a form with an attribute called product that is an array of objects

The issue is that I don't want to return the property name appended to the message, I want to return a clean message, readable for end users

export class CheckoutForm {
  @ValidateNested({ always: true })
  @Type(() => ProductForm)
  products: ProductForm[];
}
export class ProductForm {
  @IsString({ always: true, message: 'O nome do produto é obrigatório' })
  name: string;

  @Min(1, { always: true, message: 'O preço do produto é obrigatório' })
  value: number;

  @IsNotEmpty({
    always: true,
    message: 'A quantidade do produto é obrigatória',
  })
  amount: number;
}

Answer 1

Looks like this is an open issue with class-validator. https://github.com/typestack/class-validator/issues/614#issuecomment-807255434

Seems to be nested validation issues if more than one level, which would explain the issues that you are having.

Answer 2

Since 5.5.0 nestjs have a method to modify the errors on class-validator and class-transformer.

in your main.ts you should have

  await app.useGlobalPipes(new ValidationPipe());

this method receives a parameter named "exceptionFactory", which receives a function that can return an exception. if you want to modify and specific error you can do something like this

   await app.useGlobalPipes(new ValidationPipe({
    exceptionFactory: (errors: ValidationError[]) =>
    {
      const customError = errors.map((el) =>
      {
        if(el.constraints.isString)
        {
          return "O nome do produto é obrigatório"
        }

        if(el.constraints.isNotEmpty)
        {
          return "A quantidade do produto é obrigatória"
        }

      });
      
      return new HttpException(customError, HttpStatus.BAD_REQUEST);
    }
  }));

notices I have an array of errors this is because I use graphql maybe in your case in REST is different however if you console.log this errors you get an array whit this values

[
  ValidationError {
    target: SignUpInput {
      confirmPassword: '123',
      email: 'text@gmail.com',
      name: '',
      password: '123',
      surname: ' '
    },
    value: '',
    property: 'name',
    children: [],
    constraints: {
      minLength: 'name must be longer than or equal to 3 characters',
      isAlpha: 'name must contain only letters (a-zA-Z)'
    }
  }
]

in the constraints elements are the errors of the validations do you have whit this you can modify the errors.

IMPORTANT: "exceptionFactory" should return a valid exeption otherwise it wont work