Three way binding in Angular 2 and Angularfire2

Question

I am trying to three-way bind an input element to firebase database in Angular.js 2 (2.0.0-rc.4), using AngularFire 2 (2.0.0-beta.2).

I have a very simple html like:

<form (ngSubmit)="onSubmit()" #commentForm="ngForm">
  <input [(ngModel)]="model.author" type="input" name="author" required>
</form>

In my component, to save and retrieve contents of this input to firebase, I have an implementation like this:

export class CommentFormComponent implements OnInit, AfterViewInit {
  @ViewChild("commentForm") form;
  // http://stackoverflow.com/questions/34615425/how-to-watch-for-form-changes-in-angular-2

  firebaseInitComplete = false;
  model: Comment = new Comment("", "");
  firebaseForm: FirebaseObjectObservable<Comment>;

  constructor(private af: AngularFire) { }

  ngAfterViewInit() {
    this.form.control.valueChanges
      .subscribe(values => {
        // If we haven't get the initial value from firebase yet,
        // values will be empty strings. And we don't want to overwrite
        // real firebase value with empty string on page load
        if (!this.firebaseInitComplete) { return; }

        // If this is a change after page load (getting initial firebase value) update it on firebase to enable 3-way binding
        this.firebaseForm.update(values);
      });
  }

  ngOnInit() {
    this.firebaseForm = this.af.database.object("/currentComment");
    // Listen to changes on server
    this.firebaseForm.subscribe(data => {
      this.firebaseInitComplete = true; // Mark first data retrieved from server
      this.model = data;
    });
  }    
}

The code above works, I am able to read initial firebase value and update value on firebase when user type something in real time.

But having a manual logic to check for this.firebaseInitComplete and adding ngAfterViewInit to listen for changes feels a little bit wrong and I am just hacking it to work.

Is there a better implementation of three-way binding with less logic inside component?

Answer 1

Seven months later and I have an answer for you.. extended ngModel syntax..

<input [ngModel]='(model|async)?.author' (ngModelChange)="model.update({author: $event})">

The [] block is a getter and the () block is a setter. Since the model's getter is actually unwrapping the FirebaseObjectObservable, you have to use the FirebaseObjectObservable's binding to set it.