在使用angular进行json迭代时遇到问题

我尝试使用anglejs迭代以下json

"[{
\"product_id\":\"1517519077\",
\"prod_name\":\"Desktop PC Dell Precision T5610 Workstation\",
\"gpu\":\"QuadroK4000\",
\"cpu\":\"\",
\"ram_cap\":\"8\",
\"ram_type\":\"DDR3\",
\"hdd_cap\":\"500\",
\"hdd_speed\":\"7200\",
\"hdd_type\":\"HDD\",
\"display_size\":\"\",
\"display_res\":\"\",
\"price\":\"2319\",
\"cpu_rank\":\"0\",
\"cpu_rate\":\"0\",
\"gpu_rank\":\"2853\",
\"gpu_rate\":\"38\",
\"category\":\"2\",
\"tld\":\"de\",
\"feed_id\":\"1\",
\"gewicht\":null,
\"os\":null,
\"brand\":\"DELL\",
\"update_time\":null,
\"laufwerk\":null},

{\"product_id\":\"1534720291\",
\"prod_name\":\"Desktop PC Dell Precision T3610 BTX Base\",
\"gpu\":null,
\"cpu\":\"\",
\"ram_cap\":\"8\",
\"ram_type\":\"DDR3\",
\"hdd_cap\":\"500\",
\"hdd_speed\":\"7200\",
\"hdd_type\":\"HDD\",
\"display_size\":\"\",
\"display_res\":\"\",
\"price\":\"1164\",
\"cpu_rank\":\"0\",
\"cpu_rate\":\"0\",
\"gpu_rank\":null,
\"gpu_rate\":null,
\"category\":\"2\",
\"tld\":\"de\",
\"feed_id\":\"1\",
\"gewicht\":null,
\"os\":null,
\"brand\":\"DELL\",
\"update_time\":null,
\"laufwerk\":null
}]"

但我明白 Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: product in products, Duplicate key: string:" 错误

而hier是我获取和迭代数据的方式

控制器

function ProductsCtrl($scope, $http ) {
    $http({
        method: 'GET',
        url: 'http://www.someapi.com/api/restapi/products.json'
   }).success(function(data, status, headers, config) {
        // this callback will be called asynchronously       
        $scope.products = data;
        console.log($scope.products);
    }).error(function(data, status, headers, config) {
        // called asynchronously if an error occurs
        console.log(headers);
        console.log(data);
    });
}

视图迭代

<ul ng-repeat="product in products">
       <li>{{ product.prod_name }}</li>
</ul>

试用 product in products track by $index 我遇到浏览器崩溃