inherit methods in type helprs

[mohsensaremi]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

This feature is related to my issue that closed without any solution.

Previous issue:
#471

Describe the solution you'd like

We can create inheritMethods function like this:

export function inheritMethods(
  parentClass: Type<any>,
  targetClass: Function,
  isPropertyInherited?: (key: string) => boolean,
) {
  Object.getOwnPropertyNames(parentClass.prototype)
    .filter(
      (propertyName) =>
        !isPropertyInherited || isPropertyInherited(propertyName),
    )
    .forEach((name) => {
      Object.defineProperty(
        targetClass.prototype,
        name,
        Object.getOwnPropertyDescriptor(parentClass.prototype, name) ||
          Object.create(null),
      );
    });
}

and edit omit-type.helper.ts like this:

import { Type } from '@nestjs/common';
import { MappedType } from './mapped-type.interface';
import {
  inheritPropertyInitializers,
  inheritTransformationMetadata,
  inheritValidationMetadata,
  inheritMethods,
} from './type-helpers.utils';

export function OmitType<T, K extends keyof T>(
  classRef: Type<T>,
  keys: readonly K[],
): MappedType<Omit<T, typeof keys[number]>> {
  const isInheritedPredicate = (propertyKey: string) =>
    !keys.includes(propertyKey as K);

  abstract class OmitClassType {
    constructor() {
      inheritPropertyInitializers(this, classRef, isInheritedPredicate);
    }
  }

  inheritValidationMetadata(classRef, OmitClassType, isInheritedPredicate);
  inheritTransformationMetadata(classRef, OmitClassType, isInheritedPredicate);
  inheritMethods(classRef, OmitClassType, isInheritedPredicate);

  return OmitClassType as MappedType<Omit<T, typeof keys[number]>>;
}

and add inheritMethods(classRef, OmitClassType, isInheritedPredicate); too all type helpers.

Teachability, documentation, adoption, migration strategy

We just need to add this function in type-helpers.utils.ts

export function inheritMethods(
  parentClass: Type<any>,
  targetClass: Function,
  isPropertyInherited?: (key: string) => boolean,
) {
  Object.getOwnPropertyNames(parentClass.prototype)
    .filter(
      (propertyName) =>
        !isPropertyInherited || isPropertyInherited(propertyName),
    )
    .forEach((name) => {
      Object.defineProperty(
        targetClass.prototype,
        name,
        Object.getOwnPropertyDescriptor(parentClass.prototype, name) ||
          Object.create(null),
      );
    });
}

and use it in all type-helpers.

What is the motivation / use case for changing the behavior?

We can now inherit methods using type helpers

[kamilmysliwiec]

This has been discussed several times in the past and we don't plan to add such a feature to this package.