title: Ng-model's attribute in a ng-repeat input checkbox gets always literal or give error
body: <p>So i need to know the extras of a car than a user wants to include in his preferences.
  I'm trying to create input checkboxes from an array obtained by an ajax request and generate the inputs by ng-repeat. The major objective is to know the checkboxes selected by the user. I'd like that my approach to be create an auxiliar array which contains the selected ones, but i don't know how to set a unique ng-model to every item in the ng-repeat iteration so i can know the list of selected items. I guess there is something left in my knowlege of angular. Here is what i have for now.. </p>
  
  <p>In the controller...</p>
  
  <pre><code>$http.get('/ajax/ajax_get_extras/'+$scope.car.version+'/false').success(function(data) {
                  $scope.extras = data;
           });  
  $scope.addExtra = function(){ // ... manage the auxiliar array }
  </code></pre>
  
  <p>In the html ...</p>
  
  <pre><code>&lt;div ng-controller="Controller"&gt;
          &lt;form novalidate class="simple-form"&gt;
              &lt;span ng-repeat="extra in extras"&gt;
                  &lt;input  type="checkbox" ng-model="extra.id" ng-change="addExtra()" name="extra_{{extra.id}}" &gt;{{extra.name}} - &lt;strong&gt;{{extra.real_price | onlynumber | currency}}&lt;/strong&gt;
              &lt;/span&gt;
          &lt;/form&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>And i'm stuck since the extra.id doesnt transform to the real extra.id and stays as a string "extra.id" >_&lt;</p>
  
  <p>I tried <strong>extra_{{extra.id}}</strong>, <strong>extra.id</strong>, <strong>{{extra.id}}</strong>, <strong>$index</strong> as posibles ng-model and none works.</p>