如何通过angularjs $resource访问json中的嵌套对象

.NET服务部分：

[OperationContract] // route prefix 'api'
    [WebGet(UriTemplate = "users/{id}/privileges",ResponseFormat = WebMessageFormat.Json)]
    public PrivilegeSet GetPrivileges(string id)
    {
        var response = new PrivilegeSet();

        List<Role> roles = new List<Role>();
        roles.Add(new Role() { RoleId = 1,Name = "Role 1",Active = true });
        roles.Add(new Role() { RoleId = 2,Name = "Role 2",Active = true });
        roles.Add(new Role() { RoleId = 3,Name = "Role 3",Active = false });
        response.Roles = roles;

        List<SubRole> subRoles = new List<SubRole>();
        subRoles.Add(new SubRole() { SubRoleId = 1,Name = "SubRole 1",RoleId = 1,Active = true });
        subRoles.Add(new SubRole() { SubRoleId = 2,Name = "SubRole 2",Active = true });
        subRoles.Add(new SubRole() { SubRoleId = 3,Name = "SubRole 3",Active = false });
        response.SubRoles = subRoles;

        return response;
    }

JSON结构：

{
"Roles": [
{
  "Active": true,"Name": "Role 1","RoleId": 1
},{
  "Active": true,"Name": "Role 2","RoleId": 2
},{
  "Active": false,"Name": "Role 3","RoleId": 3
}
],"SubRoles": [
{
  "Active": true,"Name": "SubRole 1","RoleId": 1,"SubRoleId": 1
},"Name": "SubRole 2","SubRoleId": 2
},"Name": "SubRole 3","SubRoleId": 3
}
]
}

Angularjs服务：

angular.module('privilegeService',['ngResource']).
    factory('Privilege',function ($resource) {
        return $resource('api/users/:userId/privileges',{userId: '@id'});
    });

Angularjs获取部分：

function PrivilegesCtrl($scope,Privilege) {
    $scope.privileges = Privilege.query({userId:2}); // privileges remains empty using nested objects,with one level object works fine
    ...

当JSON具有嵌套对象时,为什么权限保持为空？以及如何在视图中访问嵌套对象？