Dropdown in angularJS

<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js"></script>
<div ng-app="test">
    <div ng-controller="DemoCtrl">
        <select ng-model="selectedRole" ng-options="Role as Role.Name for Role in Roles track by Role.Id" ng-change="GetValue()">
                                        @*ng-options="Role as Role.Name for Role in Roles"*@
                                        @*ng-options="a.Id as a.Name for a in Roles track by a.Id"*@
            <option value="">Select Account</option>
        </select>
        <br />
        @*selected Value is : {{selectedRole}}*@
    </div>
</div>
<script>
    angular.module('test', []).controller('DemoCtrl', function ($scope, $http, $window) {
        $scope.selectedRole = null;
        $scope.Roles = [];
        $scope.GetValue = function () {
            var RoleId = $scope.selectedRole.Id;
            var RoleName = $scope.selectedRole.Name;
            console.log(RoleId, RoleName);
        }
        $http({
            method: 'GET',
            url: '/Account/GetRoles',
            //data: { applicationId: 3 }
        }).success(function (result) {
            $scope.Roles = result;
            console.log($scope.Roles);
        });
    });
</script>