How to make more advanced conditional validation using class-validator?

Question

My validation requirements for one varriable depends on the value of the other varriable. I don't know how to create my DTO properly.

Look for my example:

export class CreateItemDto {
    @IsBoolean()
     price_show: boolean;
   
     @ValidateIf(o => o.price_show === true)
     @IsNumber()
     @Min(10)
     //TODO: if price_show is false, then price MUST BE NULL (or even should not be defined?). How to achieve that?
     price: number | null;
}

Answer 1

You can use @Transform decorator to set price value to null

...
import { Transform } from 'class-transformer';


export class CreateItemDto {
  @IsBoolean()
  price_show: boolean;

  @Transform(({ value, obj }) => obj.price_show ? value : null)
  @ValidateIf((o) => o.price_show === true)
  @IsNumber()
  @Min(10)
  //TODO: if price_show is false, then price MUST BE NULL (or even should not be defined?). How to achieve that?
  price: number | null;
}

Reference