How I can validate each object's field in array using class-validator in nest.js

Question

import { ArrayMaxSize, ArrayMinSize, IsArray, IsBoolean, IsString, ValidateNested } from "class-validator";
import { Transform, Type } from "class-transformer";

class CreateAnswerDto {
  @IsBoolean()
  readonly isTrue: string;

  @IsString()
  title: string;

  @IsString()
  description: string;
}

const transformAnswers = answers => {
  return JSON.parse(answers.value);
};

export class CreateQuestionDto {
  @Transform(transformAnswers, { toClassOnly: true })
  @IsArray()
  @ArrayMinSize(4)
  @ArrayMaxSize(4)
  @ValidateNested({ each: true })
  @Type(() => CreateAnswerDto)
  readonly answers: CreateAnswerDto[];

  @IsString()
  readonly title: string;
}

So I have the same code, and I want to validate each object field in answers, but this code doesn't work. If I send the wrong data this validation skips it. How can I correct validate my answers?

Thanks for any help!

Did you try this? https://stackoverflow.com/questions/58343262/class-validator-validate-array-of-objects The first answer worked for me — Reut Schremer, Dec 23 '21 at 08:26
Yes, I did. It works for me without @Transform(transformAnswers, { toClassOnly: true }) and when I send answers as an array. But I need to send it using formData and need to stringify answers. Then I need to transform these stringified answers to an array and validate it. But after transform validation doesn't work — Ihor, Dec 23 '21 at 15:04
Does this answer your question? [Convert stringified JSON to Object using class-transformer](https://stackoverflow.com/questions/67884350/convert-stringified-json-to-object-using-class-transformer) — Lars Flieger, Dec 25 '21 at 00:41

score 2 · Answer 1 · answered Dec 26 '21 at 02:01

So, I resolved this problem.

import {
  ArrayMaxSize,
  ArrayMinSize,
  IsArray,
  IsNotEmpty,
  IsString,
  IsUUID,
  MinLength,
  ValidateNested,
} from "class-validator";
import { plainToClass, Transform, Type } from "class-transformer";
import { CreateAnswerDto } from "src/modules/answers/dto/create-answer.dto";
import { HasMimeType, IsFile, MaxFileSize, MemoryStoredFile } from "nestjs-form-data";

export class CreateQuestionDto {
  @ValidateNested({ each: true })
  @Transform(({ value }) => plainToClass(CreateAnswerDto, JSON.parse(value)))
  @IsArray()
  @ArrayMinSize(4)
  @ArrayMaxSize(4)
  @Type(() => CreateAnswerDto)
  readonly answers: CreateAnswerDto[];

  @IsUUID()
  @IsNotEmpty()
  readonly category_id: string;

  @IsFile()
  @MaxFileSize(220000)
  @HasMimeType(["image/jpeg", "image/png"])
  readonly image: MemoryStoredFile;

  @IsString()
  @MinLength(5)
  readonly title: string;
}

And my Answers dto:

import { Exclude } from "class-transformer";
import { IsBoolean, IsNotEmpty, IsString, MinLength } from "class-validator";

export class CreateAnswerDto {
  @IsBoolean()
  @IsNotEmpty()
  readonly isTrue: boolean;

  @IsString()
  @MinLength(5)
  readonly title: string;

  @IsString()
  @MinLength(5)
  readonly description: string;

  @IsString()
  @MinLength(5)
  readonly displayMessage: string;

  @Exclude()
  readonly id: string;

  constructor(partial: Partial<CreateAnswerDto>) {
    Object.assign(this, partial);
  }
}

How I can validate each object's field in array using class-validator in nest.js

1 Answers1