Validating nested objects with class-validator in NestJS

#nestjs #typescript #javascript #node

Today I have for you a quick and short article. Maybe it will help someone. I'm using class-validator for request validation in NestJS really often. A few days ago I needed to validate a nested object. Quick look to the class-validator validation:

If your object contains nested objects and you want the validator to perform their validation too, then you need to use the @ValidateNested() decorator:

import { ValidateNested } from 'class-validator';

export class Post {
  @ValidateNested()
  user: User;
}

But for some reason It doesn't work in NestJS! Here is an easy solution. Install class-transformer package, if you haven't done it yet. Then import @Type() decorator, and declare the type of validating object with it. Check this out:

import { ValidateNested } from 'class-validator';
import { Type } from 'class-transformer';

export class Post {
  @ValidateNested()
  @Type(() => User)
  user: User;
}

Now our NestJS application will validate User object correctly. If you need to validate an array of objects, use each: true:

export class User {
  @ValidateNested({ each: true })
  @Type(() => Post)
  posts: Post[];
}

Hope it will be useful for you! Cheers!

Top comments (24)

dan's cat • Oct 7 '21 • Edited on

I had received this error

TypeError: Cannot convert undefined or null to object

after I wrote something like this

  @IsArray()
  @ArrayNotEmpty()
  @ValidateNested({ each: true })
  @Type(() => UserDto)
  items: UserDto[]

Why its does not work for me 😢

Krzysztof Szala • Oct 7 '21

Are you sure that items property is not null / undefined? Maybe it didn't come in the request?

dan's cat • Dec 22 '21

Finally I knew why it wasn't work for me. Because I wrote nested object in array more than couple layers. By the way I have fixed it by customized validate pipe when it received bad request exception. Now it works for me!

oliverqueen2003 • Sep 12 '22

Can you share your code?

Navin Mishra • Oct 10 '22

i could solve this problem with the help of custom recursive function in global validation pipe like this:

helper.js

and in main.ts

Albert • Mar 24 '22

What about disallowing nested arrays within the array?

@ValidateNested({each: true})
@Type(() => myType)
myProp: myType[]

allows the property to be both an array of arrays, or an array of objects with the form of myType, instead of only allowing it to be an array of objects.

Diwakar • Dec 12 '22 • Edited on

Any solution for this? I want to allow only objects. @avantar

Volodymyr83 • Sep 22 '22 • Edited on

Hi. Great article! But if an object in the array doesn't pass validation, I receive only
{
"statusCode": 500,
"message": "Internal server error"
}
How to get message with exact validation error?