/// <summary>
/// 通过指定登录名获取授权角色名称数据集合
/// </summary>
/// <param name="userName">登录名</param>
/// <returns></returns>
public override IEnumerable <string> RetrievesByUserName(string userName)
{
var user = UserHelper.RetrieveUserByUserName(userName) as User;
return(user == null ? new string[0] : RoleHelper.Retrieves().Where(r => user.Roles.Any(ur => ur == r.Id)).Select(r => r.RoleName));
}