Forced Checkbox Example

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  isSelectedAll: false,
  isIndeterminate: true,
  
  options: [
    Ember.Object.create({
      label: 'First',
      isSelected: false
    }),
    Ember.Object.create({
    	label: 'Second',
      isSelected: true,
    })
  ],

  actions: {
  	selectAllDidChange(e) {
      const selectAllValue = e.target.checked;
      this.get('options').setEach('isSelected', selectAllValue);
    	this.set('isSelectedAll',selectAllValue);
  	},
    
    optionDidChange(option, e) {
      option.set('isSelected', e.target.checked);
      const options = this.get('options');
      const selectedOptions = options.filterBy('isSelected');
      
      if (selectedOptions.length === options.length) {
        this.set('isSelectedAll', true);
        this.set('isIndeterminate', false);
      } else if (selectedOptions.length === 0) {
       	this.set('isSelectedAll', false);
        this.set('isIndeterminate', false);
      } else {
        this.set('isSelectedAll', false);
        this.set('isIndeterminate', true);
      }
  	}
  }
});

templates.application.hbs

{{input type="checkbox"
        checked=isSelectedAll
        indeterminate=isIndeterminate
        change=(action "selectAllDidChange")}}
Selected All
<hr>
{{#each options as |option|}}
  <div>
    {{input type="checkbox"
            checked=option.isSelected
            change=(action "optionDidChange" option)}}
    {{option.label}}
    selected: {{option.isSelected}}
  </div>
{{/each}}

twiddle.json

{
  "version": "0.13.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}