mscorlib.dll中发生未处理的“System.StackOverflowException”类型的异常附加信息：集合具有固定大小

Question

我需要一些我正在进行的MVC项目的帮助。我正在尝试创建一个卖家或买家类型的用户。我创建了多对多的关系，因为用户既可以是卖家也可以是买家。我的问题是插入我继续获得以下错误的角色类型

  

mscorlib.dll中出现未处理的“System.StackOverflowException”类型异常附加信息：集合属于   固定大小。

以下是我正在使用的代码

UserController中

[HttpPost]
public ActionResult CreateUser(UserModel data, string SellerType)
{
    try     
    {
        if(SellerType == "Buyer")
        {
            userType = 2;
        }
        else if (SellerType=="Seller")
        {
            userType = 3;
        }
        data.myUser.DateCreated = DateTime.Now;
        new UsersService.UserBLClient().RegisterUser(data.myUser, userType);   
    }
    catch
    {
        return View();
    }
    return RedirectToAction("Index", "Home");
}

服务引用

public RegistrationOutcome RegisterUser(Person newPerson,int userTypeId)
{
    if (DoesUserNameExist(newPerson.Username) == true)
    {
        return RegistrationOutcome.UsernameExists;
        throw new Exception("Username has already been registered");
    }
    if (DoesEmailExist(newPerson.Email) == true)
    {
        return RegistrationOutcome.EmailExists;
        throw new Exception("Email has already been registered");
    }
    else
    {
        DaRole rr = new DaRole();
        DaUser ur = new DaUser();
        rr.DataContext = ur.DataContext;
        ur.RegisterUser(newPerson);
        rr.AllocateUser(newPerson, rr.GetRoleById(userTypeId));
        return RegistrationOutcome.Success;
    }
}

插入和获取用户角色

public void AllocateUser(Person newPerson, UserType roleType )
{
    newPerson.UserType.Add(roleType);
    DataContext.SaveChanges();
}

public UserType GetRoleById(int id)
{
    return DataContext.UserType.SingleOrDefault(x => x.RoleID == id);
}