AngularJS Chained Selects

HTML

<div ng:app ng:controller="SelectController">
  <select ng:model="category" ng:options="c.name for c in sampleProductCategories"></select>
  <select ng:model="categoryItem" ng:options="p.name for p in category.products"></select>
  <hr />
    
  category={{category.name}}<br />
  product={{categoryItem.name}}
    price = {{categoryItem.price}}
    <br/>
    foo={{category}}
</div>

CSS

</style>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.0-beta.2/angular.min.js"></script>
<style>
.ng-invalid { border: 1px solid red; } 
body { font-family: Arial,Helvetica,sans-serif; }
body, td, th { font-size: 14px; margin: 0; }
table { border-collapse: separate; border-spacing: 2px; display: table; margin-bottom: 0; margin-top: 0; -moz-box-sizing: border-box; text-indent: 0; }
a:link, a:visited, a:hover { color: #5D6DB6; text-decoration: none; }
.error { color: red; }

JavaScript

function SelectController() {
        this.category = {};
        this.categoryItem = {};
        // Data taken from KnockoutJs cart example
        this.sampleProductCategories = [
          {
            "products": [
              {
                "name": "1948 Porsche 356-A Roadster",
                "price": 53.9
              },
              {
                "name": "1948 Porsche Type 356 Roadster",
                "price": 62.16
              },
              {
                "name": "1949 Jaguar XK 120",
                "price": 47.25
              }
            ],
            "name": "Classic Cars"
          },
          {
            "products": [
              {
                "name": "1936 Harley Davidson El Knucklehead",
                "price": 24.23
              },
              {
                "name": "1957 Vespa GS150",
                "price": 32.95
              },
              {
                "name": "1960 BSA Gold Star DBD34",
                "price": 37.32
              }
            ],
            "name": "Motorcycles"
          },
          {
            "products": [
              {
                "name": "1900s Vintage Bi-Plane",
                "price": 34.25
              },
              {
                "name": "1900s Vintage Tri-Plane",
                "price": 36.23
              },
              {
                "name": "1928 British Royal Navy Airplane",
                "price": 66.74
              },
              {
                "name": "1980s Black Hawk Helicopter",
                "price": 77.27
              },
              {
                "name": "ATA: B757-300",
                "price": 59.33
              }
            ],
            "name": "Planes"
          }
        ];
    }