Q:

@Input: Two way data binding not working

I am trying to replicate this: http://plnkr.co/edit/OB2YTMJyeY3h9FOaztak?p=preview (this plunker is the example that works, and I want to get the same result but with my code, that isn't working)
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I have this simple two way binding, I am trying to update a string property such on the parent as on the child
The problem: when clicking "update from parent", both bindings update. But when clicking "update from child", only the childs updates!
This seems very simple, what can I be doing wrong?
(Note: I used angular CLI for running up the project)
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Parent component:
import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'app-my-dad',
  templateUrl: './my-dad.component.html',
  styleUrls: ['./my-dad.component.css']
})
export class MyDadComponent {

  parentModel: string;

  constructor() {}

  updateModel(){
    this.parentModel += ' parent';
  }
}

Parent template
<h2>Parent: {{ parentModel }} </h2> 
<button (click)="updateModel()"> update from parent </button>

<app-my-child [(model)]="parentModel"></app-my-child>

Child component
import { Component, OnInit, Input } from '@angular/core';

@Component({
  selector: 'app-my-child',
  templateUrl: './my-child.component.html',
  styleUrls: ['./my-child.component.css']
})
export class MyChildComponent {

  @Input() model: string;

  constructor() { }

  updateModel(){
    this.model += ' child';
  }
}

Child template:
<h2>Child: {{ model }} </h2>
<button (click)="updateModel()"> update from child </button>

A:

For two-way-binding using the [(xxx)] (banana-in-a-box) syntax, you need an @Input() and an @Output() with matching names like:
@Input() myProp:String;
@Output() myPropChange:EventEmitter<String> = new EventEmitter<String>();

See also the guide https://angular.io/docs/dart/latest/guide/template-syntax.html#!#two-way
For two-way-binding with ngModel to work, your component needs to implement ControlValueAccessor.
See also:

https://angular.io/docs/ts/latest/api/forms/index/NgModel-directive.html
https://github.com/angular/angular/issues/11073#issuecomment-242563788

