Inheriting Validation Decorators

When you define a subclass that extends from another class, the subclass will automatically inherit the parent's decorators. If a property is redefined in the descendant class, decorators will be applied from both its own class and the base class.

Example

import { validate } from 'class-validator';

class BaseContent {
    @IsEmail()
    email: string;

    @IsString()
    password: string;
}

class User extends BaseContent {
    @MinLength(10)
    @MaxLength(20)
    name: string;

    @Contains('hello')
    welcome: string;

    @MinLength(20)
    password: string;
}

let user = new User();

user.email = 'invalid email'; // inherited property
user.password = 'too short'; // password will be validated against IsString and MinLength
user.name = 'not valid';
user.welcome = 'helo';

validate(user).then(errors => {
    // handle errors
}); // it will return errors for email, password, name and welcome properties

Inheritance Rules

1. All decorators from the base class are inherited
2. Decorators can be overridden in the child class
3. Multiple decorators are combined when a property is redefined
4. Inheritance works with multiple levels of inheritance