尝试将用户添加到 MVC 中的角色 ASP.NET.更改未保存

我正在开发的应用程序涉及能够将用户添加到各种角色。现在，我可以创建用户和角色，以及查看在我的种子数据中分配给用户的角色。但是，当我尝试通过应用程序本身将用户添加到角色时，更改实际上并没有保存回数据库。我没有收到任何类型的错误页面。这是我认为是相关代码的内容。

我的帐户控制器中的用户角色方法：

[Authorize(Roles = "Admin")]
    public ActionResult UserRoles(string id)
    {
        var Db = new ApplicationDbContext();
        var user = Db.Users.First(u => u.UserName == id);
        var model = new SelectUserRolesViewModel(user);
        return View(model);
    }
    [HttpPost]
    [Authorize(Roles = "Admin")]
    [ValidateAntiForgeryToken]
    public ActionResult UserRoles(SelectUserRolesViewModel model)
    {
        if (ModelState.IsValid)
        {
            var idManager = new IdentityManager();
            var Db = new ApplicationDbContext();
            var user = Db.Users.First(u => u.UserName == model.UserName);
            idManager.ClearUserRoles(user.Id);
            foreach (var role in model.Roles)
            {
                if (role.Selected)
                {
                    idManager.AddUserToRole(user.Id, role.RoleName);
                }
            }
            return RedirectToAction("IndexUser");
        }
        return View();
    }

身份管理器类：

public class IdentityManager
{
    public bool AddUserToRole(string userId, string roleName)
    {
        var um = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));
        var idResult = um.AddToRole(userId, roleName);
        return idResult.Succeeded;
    }
    public void ClearUserRoles(string userId)
    {
        var um = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(new ApplicationDbContext()));
        var user = um.FindById(userId);
        var currentRoles = new List<IdentityUserRole>();
        currentRoles.AddRange(user.Roles);
        foreach (var role in currentRoles)
        {
            um.RemoveFromRole(userId, role.RoleId);
        }
    }
}

模型类：

public class SelectUserRolesViewModel
{
    // Enable initialization with an instance of ApplicationUser:
    public SelectUserRolesViewModel(ApplicationUser user)
        : this()
    {
        this.UserName = user.UserName;
        var Db = new ApplicationDbContext();
        // Add all available roles to the list of EditorViewModels:
        var allRoles = Db.Roles;
        foreach (var role in allRoles)
        {
            var rvm = new SelectRoleEditorViewModel(role);
            this.Roles.Add(rvm);
        }
        // Set the Selected property to true for those roles for 
        // which the current user is a member:
        foreach (var userRole in user.Roles)
        {
            var checkUserRole = this.Roles.Find(r => r.RoleID == userRole.RoleId);
            checkUserRole.Selected = true;
        }
    }
    public string UserName { get; set; }
    public List<SelectRoleEditorViewModel> Roles { get; set; }
}
// Used to display a single role with a checkbox, within a list structure:
public class SelectRoleEditorViewModel
{
    public SelectRoleEditorViewModel() { }
    public SelectRoleEditorViewModel(IdentityRole role)
    {
        this.RoleName = role.Name;
        this.RoleID = role.Id;
    }
    public bool Selected { get; set; }
    [Required]
    public string RoleName { get; set; }
    [Required]
    public string RoleID { get; set; }
}

现在我知道 AddUserToRole 方法有效，因为我在为数据库播种时直接调用它并且它有效。有人有什么想法吗？

为了完全披露，此代码取自以下教程：http://www.codeproject.com/Articles/682113/Extending-Identity-Accounts-and-Implementing-Rol

编辑：关于网页中实际发生的事情的更多描述。当我导航到将角色分配给所选用户的页面时，它会列出所有角色并预先检查用户已分配到的所有角色。我可以进行一些更改，然后单击保存按钮。但是，此时，它返回相同的视图，但没有任何用户角色信息。然后我可以再次单击保存，它会返回到用户列表页面。所以我想正在发生的事情是，当页面首次提交时，当附加了模型值（用户和角色）时，模型状态总是返回无效，因此它绕过了 UserRoles 方法中的所有代码并直接进入错误处理返回 View（） 行在最后。但是，我不知道为什么该模型无效。用户无处输入可能违反某种数据库或网页验证的值。每个角色旁边都有简单的复选框，用于指示要将用户分配到哪些角色。

[HttpPost]
[Authorize(Roles = "Admin")]
[ValidateAntiForgeryToken]
public ActionResult UserRoles(SelectUserRolesViewModel model)
{
    if (ModelState.IsValid)
    {
        var idManager = new IdentityManager();
        var Db = new ApplicationDbContext();
        var user = Db.Users.First(u => u.UserName == model.UserName);
        idManager.ClearUserRoles(user.Id);
        foreach (var role in model.Roles)
        {
            if (role.Selected)
            {
                idManager.AddUserToRole(user.Id, role.RoleName);
            }
        }
        Db.SaveChanges(); //for saving changes to the database 
        return RedirectToAction("IndexUser");
    }
    return View();
}

if (model.Roles == null)
{
     model.Roles = new Role();
}
  else {
foreach (var role in model.Roles)
        {
            if (role.Selected)
            {
                idManager.AddUserToRole(user.Id, role.RoleName);
            }
        }
 }

public class IdentityManager
{
    private ApplicationDbContext context;
    public IdentityManager ()
    {
        context = new ApplicationDbContext(); // if none supplied
    }
    public IdentityManager (ApplicationDbContext applicationDbContext)
    {
        context = applicationDbContext;
    }
    public bool AddUserToRole(string userId, string roleName)
    {
        var um = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(context));
        var idResult = um.AddToRole(userId, roleName);
        return idResult.Succeeded;
    }
    public void ClearUserRoles(string userId)
    {
        var um = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(context));
        var user = um.FindById(userId);
        var currentRoles = new List<IdentityUserRole>();
        currentRoles.AddRange(user.Roles);
        foreach (var role in currentRoles)
        {
            um.RemoveFromRole(userId, role.RoleId);
        }
    }
}

var Db = new ApplicationDbContext();
var idManager = new IdentityManager(Db);
var user = Db.Users.First(u => u.UserName == model.UserName);
idManager.ClearUserRoles(user.Id);
foreach (var role in model.Roles)
{
    if (role.Selected)
    {
        idManager.AddUserToRole(user.Id, role.RoleName);
    }
}