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? stackoverflow.com/questions/58343262/… The first answer worked for me — Reut Schremer
– Reut Schremer, Commented Dec 23, 2021 at 8:26
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
– Ihor, Commented Dec 23, 2021 at 15:04
Does this answer your question? Convert stringified JSON to Object using class-transformer — Lars Flieger
– Lars Flieger, Commented Dec 25, 2021 at 0:41

Ihor · Accepted Answer · 2021-12-26 02:01:56Z

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);
  }
}

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