Advanced conditions with class-validator (possible)?

Question

I have TypeScript NestJS project.

I need to validate incoming DTO to my API. It can be described as "creating of project" where we have type of building (House, Flat, Garden) and depending on that type we need to define:

House: FLOORS including ROOMS
Flat: ROOMS
Garden: nothing (it is one "room")

Example of house type:

{
  type: HOUSE,
  floors: [
    {
      name: "1st floor",
      rooms: [
        {
          name: "bedroom"
        }
      ]
    }
  ]
}

Example of flat type:

{
  type: FLAT,
  rooms: [
    {
      name: "bedroom"
    }
  ]
}

I've done this in past with help of AJV, but now as we migrated to NestJS, we started using class-validator.

My question is, if I can make those advanced conditionals (eg. when type is FLAT, then expect ROOMS only, but not FLOORS) in class-validator?

score 4 · Answer 1 · answered Feb 14 '20 at 16:30

4

With class-validator you have the options of Conditional Validation and of Group Validation, or you could always create a custom pipe and use AJV as you are used to. For the conditional validation you could create validations based on type and then let class-validator take care of the rest

answered Feb 14 '20 at 16:30

Jay McDoniel

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"you could create validations based on type", can you show an example? – coler-j Mar 10 '20 at 16:21
@coler-j if I can figure out what I was meaning, then absolutely. I'm pretty sure I've seen examples _somewhere_, but I can't recall where at the moment – Jay McDoniel Mar 10 '20 at 16:53
3

This doesn't help at all. I'm also want to do the same thing. I only find basic examples which are all just copies from docs and nothing more advanced like the example in question. Saying there are "examples somewhere" doesn't say much as well. – Alko Dec 20 '21 at 11:04

score 2 · Answer 2 · answered Dec 21 '21 at 05:33

You have to create a custom validator for that. The docs are pretty good: https://github.com/typestack/class-validator#custom-validation-classes

When you create your custom validator class, in your implementation of validate you can access the other parameter beeing validated in the args argument. Just write your if statements and return false if they are not met. You can even return your custom error messages and implement your own decorator.

score 0 · Answer 3 · answered Jul 20 '22 at 12:13

I had similar requirements. If you're okay to nest the incoming object by one level, following pattern should work.

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

class MyRequestDto {
  @IsNotEmptyObject()
  @ValidateNested()
  @Type(null, {
    keepDiscriminatorProperty: true,
    discriminator: {
      property: 'type',
      subTypes: [
        {
          name: 'Flat',
          value: Flat,
        },
        {
          name: 'Room',
          value: Room,
        },
        {
          name: 'Garden',
          value: Garden,
        },
      ],
    },
  })
  entity: Flat | Room | Garden;
}

We can use the Type decorator provided by the class-transformer and pass in the discriminator option, which takes the property and subTypes attributes.

property is the propertyName to use for establishing the type of incoming of the incoming object.
subTypes will have the corresponding value (name) for the property and the class (value) to use for validation.

The interface definition can be found here

`TS2345: Argument of type 'null' is not assignable to parameter of type '((type?: TypeHelpOptions | undefined) => Function) | undefined'.` How did it work for you? — mike927, Feb 24 '23 at 15:22

score 0 · Answer 4 · answered May 23 '23 at 17:26

I use this kind of validation for nasted objects:

export class PredefinedProductsDao {

  @IsEnum(ProductEnum)
  product: ProductEnum;

  @IsObject()
  @ValidateNested()
  @Type((type: TypeHelpOptions | undefined) => {
    if (type?.object) {
      const predefinedProductsDao: PredefinedProductsDao =
        type.object as PredefinedProductsDao;
      switch (predefinedProductsDao.editor) {
        case ProductEnum.FIRST:
          return FirstProductDao;
        case ProductEnum.SECOND:
          return SecondProductDao;
      }
    }
    return FirstProductDao;
  })
  predefinedConfig: FirstProductDao | SecondProductDao;
}

In my case I want validate predefinedConfig to be one of DAOs, different for each product. It's working as a shae

Advanced conditions with class-validator (possible)?

4 Answers4