Set null as empty string value for input field

Issue

I have an input field mapped to an entity in my controller with a ngModel 2-way binding:

<input type="text" [(ngModel)]="entity.one_attribute" />

When I initialize my controller, I have this entity:

{ one_attribute: null }

If a user starts to fill in the field but does not submit the form immediately and empties the field, my entity is updated to become:

{ one_attribute: "" }

Is it possible to define that empty string should be changed to null automatically?

Solution

After viewing a bunch of answers about ValueAccessor and HostListener solutions, I made a working solution (tested with RC1):

import {NgControl} from "@angular/common";
import {Directive, ElementRef, HostListener} from "@angular/core";

@Directive({
  selector: 'input[nullValue]'
})
export class NullDefaultValueDirective {
  constructor(private el: ElementRef, private control: NgControl) {}

  @HostListener('input', ['$event.target'])
  onEvent(target: HTMLInputElement){
    this.control.viewToModelUpdate((target.value === '') ? null : target.value);
  }
}

Then use it that way on your input fields:

<input [(ngModel)]="bindedValue" nullValue/>

Answered By - jobou