Question

使用Asp.net MVC 4和EF 5.0

问题：

每当我在下拉列表中选择一个用户并将帖子提交给Action时。发生了两件事：

用户被添加到DinnerEvent中，应该是：
选中的用户是重复的，因此我现在在数据库的User表中有两个用户实例。这很糟糕。：（

以下是设置

我创建了两个实体：晚餐活动和用户

DinnerEvent类具有指向一组服务员（用户）的导航属性

public virtual ICollection<User> Attendants { get; set; }

我为DinnerEvent和Users

DinnerEvent控制器

AddAttendantToEvent操作

[HttpPost]
public ActionResult AddAttendantToEvent(int users  , int EventID )
{
    if (ModelState.IsValid)
    {
        var user = userRepository.Find(users);
        dinnereventRepository.Find(EventID).Attendants.Add(user); //Add the User to the Event.
        dinnereventRepository.Save();
        return RedirectToAction("Index");
    }
    else
    {
        return View();
    }
}

视图 - 迭代所有事件，并添加一个填充了所有用户foreach事件的下拉列表。



 @model Madklub.Models.ViewModel

 @foreach (var item in Model.events) {

 //Code to display available events

     @using (Html.BeginForm("AddAttendantToEvent", "DinnerEvents")) {

     @Html.Hidden("EventID", item.DinnerEventID);
     @Html.DropDownListFor(m => m.users, new SelectList(Model.users, "UserID", "RoomNumber"));

     <input type="submit" value="Add" />
}


ViewModel:

public class ViewModel
{
    public IQueryable<DinnerEvent> events { get; set; }
    public IQueryable<User> users { get; set; }
}


which is initialized like this:

Index Action in DinnerEventController: 

public ViewResult Index()
{
    ViewModel viewdata = new ViewModel();
    viewdata.events = dinnereventRepository.AllIncluding(m => m.Attendants);
    viewdata.users = userRepository.All;
    return View(viewdata);
}


What am I doing wrong?

@model Madklub.Models.ViewModel @foreach (var item in Model.events) { //Code to display available events @using (Html.BeginForm("AddAttendantToEvent", "DinnerEvents")) { @Html.Hidden("EventID", item.DinnerEventID); @Html.DropDownListFor(m => m.users, new SelectList(Model.users, "UserID", "RoomNumber")); <input type="submit" value="Add" /> }

请求的存储库代码：

缩小为仅包含Save（）方法。

请注意，这是Scaffolding的所有自动生成的代码。

public class ViewModel
{
    public IQueryable<DinnerEvent> events { get; set; }
    public IQueryable<User> users { get; set; }
}

Answer 1

工作单元模式:(顺便说一下，让你的repo / uow IDisposable，以便你可以清理DbContext实例）

public class DinnerEventRepository : IDinnerEventRepository
{
    MadklubContext _context = new MadklubContext();

    public void Save()
    {
        _context.SaveChanges();
    }  

    public DinnerEventRepository( MadklubContext context = null )
    {
        _context = context ?? new MadklubContext();
    }      
}

public class UserRepository //: IUserRepository
{
    MadklubContext _context = new MadklubContext();

    public void Save()
    {
        _context.SaveChanges();
    }  

    public UserRepository( MadklubContext context = null )
    {
        _context = context ?? new MadklubContext();
    }      
}

public class RsvpUnitOfWork // come up with a better name
{
    MadklubContext _context = new MadklubContext();

    public DinnerEventRepository DinnerEventRepo { get; private set; }
    public UserRepository UserRepo { get; private set; }

    public RsvpUnitOfWork()
    {
        DinnerEventRepo = new DinnerEventRepository( _context );
        UserRepo = new UserRepository( _context );
    }

    public void Save()
    {
        _context.SaveChanges();
    }
}

用法：

[HttpPost]
public ActionResult AddAttendantToEvent(int users  , int EventID )
{
    if (ModelState.IsValid)
    {
        // this should be a using statement once you implement IDisposable
        // e.g. using( var uow = new RsvpUnitOfWork() ) { ... }
        var uow = new RsvpUnitOfWork();
        // you need to validate that user != null
        var user = uow.UserRepo.Find(users);
        // possible null reference exception if dinner event not found for EventID
        uow.DinnerEventRepo.Find(EventID).Attendants.Add(user); //Add the User to the Event.
        uow.Save();
        return RedirectToAction("Index");
    }
    else
    {
        return View();
    }
}

ASP.net MVC EF Codefirst重复条目

1 个答案: