Example of a computed property using @each

example.js

MyApp.Project = SC.Record.create({

  tasks: SC.Record.toMany(...),

  tasksNeedUpdate: 0,
  tasksDidUpdate: function() {
    this.set('tasksNeedUpate', this.get('tasksNeedUpdate') + 1);
  }.observes('*[email protected]'),

  allTasksCompleted: function() {
    return this.get('tasks').everyProperty('isComplete', true);
  }.property('tasksNeedUpdate')

});