asp.net-mvc – 为什么UserManager.CreateIdentityAsync()正在寻找IdentityRole以及如何修复？

我正在使用Identity2.0和MVC5 CodeFirst我已经扩展了IdentityUser和IdentityRole,如下所示：

public class ApplicationUser : IdentityUser
{
    [required]
    [StringLength(50)]
    public string FirstName { get; set; }

    [required]
    [StringLength(50)]
    public string LastName { get; set; }
}

public class ApplicationRole : IdentityRole
{
    [required]
    [StringLength(50)]
    public string ProperName { get; set; }

    [required]
    public string Description { get; set; }
}

public class MyAppDb : IdentityDbContext<ApplicationUser,ApplicationRole,string,IdentityUserLogin,IdentityUserRole,IdentityUserClaim>
{
    public MyAppDb()
        : base("MyAppDb")
    {
    }
}

注意MyAppDb继承自IdentityDbContext但我传递的是ApplicationRole而不是IdentityRole.我的ApplicationRole继承自IdentityRole,所以这应该不是问题.

但…

我的AccountController抛出了这个错误：

The entity type IdentityRole is not part of the model for the current context.

在此代码中的UserManager.CreateIdentityAsync(…)：

private async Task SignInAsync(ApplicationUser user,bool isPersistent)
{
     AuthenticationManager.SignOut(DefaultAuthenticationTypes.ExternalCookie);
     var identity = await UserManager.CreateIdentityAsync(user,DefaultAuthenticationTypes.ApplicationCookie);
     AuthenticationManager.SignIn(new AuthenticationProperties() { IsPersistent = isPersistent },identity);
}

用户正在这里创建：

var user = await UserManager.FindAsync(model.UserName,model.Password);
        if (user != null)
        {
            await SignInAsync(user,model.RememberMe);
            return RedirectToLocal(returnUrl);
        }

什么是“重大故障”？