尝试登录时（当用户未登录时）通过asp.net mvc 5中的电子邮件获取Userrule

Question

public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
    {
        if (!ModelState.IsValid)
        {
            return View(model);
        }


        var result = await SignInManager.PasswordSignInAsync(model.Email,    model.Password,model.RememberMe, shouldLockout: false);

        ApplicationDbContext db = new ApplicationDbContext();

        var UserID= from u in db.Users
                    where u.Email == model.Email
                    select u.Id;
 var RolesForUser = await UserManager.GetRolesAsync(UserID);


    }

“注意=＆gt;用户未登录。我希望用户尝试登录时通过电子邮件发送用户ID。我会查询并获取UserID bur异常来自UserID为空”