ASP.Net MVC 和状态 - 如何从双列表框中的会话更改更新数据库？

Question

我正在开发一个双列表框系统，操作员可以在该系统中为特定用户分配和删除不同的练习。对于 RemoveExercises 函数，我已经开始使用 Session 以便 RequestedExercises 列表框随着所做的更改（添加和删除练习）而更新。

目前AddExercises 函数将练习从AvailableExercises 列表框添加到数据库上的RequestedExercises 列表框（也称为RegimeItems），但它不会显示在RequestedExercises 列表框上，直到我返回页面。

但是，RemoveExercises 函数会从RequestedExercises 列表框中删除选定的练习，但不会对数据库进行更改。所以这两个函数只做了我希望它们做的一半，但方式不同。

这让我相信，由于会话状态，添加的练习没有显示在 RequestedExercises 列表框中，并且 RemoveExercises 没有更新其对数据库的更改。任何帮助将不胜感激。

更新：在帖子请求中将return View(model); 更改为return RedirectToAction("ExerciseIndex", new { id = model2.UserID, vmodel = model2 }); 后，添加练习效果很好。 我应该如何让 RemoveExercises 对域对象 User 起作用？

Controller.cs

    [HttpGet]
    public ActionResult ExerciseIndex(int id, UserExerciseViewModel vmodel)
    {
        User user = db.Users.Find(id);
        UserExerciseViewModel model = new UserExerciseViewModel { AvailableExercises = GetAllExercises(), RequestedExercises = ChosenExercises(user, vmodel) };
        model.UserID = user.UserID;
        Session["UserExerciseViewModel"] = model;
        return View(model);
    }

    [HttpPost]
    public ActionResult ExerciseIndex(UserExerciseViewModel model, string add, string remove, string send, int id, RegimeItem item)
    {
        UserExerciseViewModel model2 = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
        model.RequestedExercises = model2.RequestedExercises;
        model.AvailableExercises = model2.AvailableExercises;
        if (!string.IsNullOrEmpty(add))
            AddExercises(model, id);
        else if (!string.IsNullOrEmpty(remove))
            RemoveExercises(model, id);
        User user = db.Users.Find(model2.UserID);
        model2.RequestedExercises = ChosenExercises(user, model);
        user.RegimeItems = model.RequestedExercises;
        RestoreSavedState(model, user);
        return RedirectToAction("ExerciseIndex", new { id = model2.UserID, vmodel = model2 });
    )

    void RemoveExercises(UserExerciseViewModel model, int id)
    {
        var userExerciseViewModel = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
        foreach (int selected in model.RequestedSelected)
        {
            RegimeItem item = model.RequestedExercises.FirstOrDefault(i => i.RegimeItemID == selected);
            if (item != null)
            {
                model.RequestedExercises.Remove(item);
            }
        }
        db.SaveChanges();
    }

    void AddExercises(UserExerciseViewModel model, int id)
    {
        var userExerciseViewModel = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
        foreach (int selected in model.AvailableSelected)
        {
            if (model.AvailableSelected != null)
            {
                User user = db.Users.Find(id);
                user.RegimeItems.Add(new RegimeItem()
                {
                    RegimeExercise = (this.GetAllExercises().FirstOrDefault(i => i.ExerciseID == selected))
                });
            }
        }
        db.SaveChanges();
    }

    void RestoreSavedState(UserExerciseViewModel model, User user)
    {
        user.RegimeItems = this.ChosenExercises(user, model);
        if (!string.IsNullOrEmpty(model.SavedRequested))
        {
            string[] exIds = model.SavedRequested.Split(',');
            var regimeItems = ChosenExercises(user, model).Where(p => exIds.Contains(p.RegimeItemID.ToString()));
            model.RequestedExercises.AddRange(regimeItems);
        }
        db.SaveChanges();
    }

    private List<Exercise> GetAllExercises() //Gets all the data for AvailableExercises
    {
        return db.Exercises.ToList();
    }

    private List<RegimeItem> ChosenExercises(User user, UserExerciseViewModel model) //Gets all the data for RequestedExercies
    {
     return db.Users
     .Where(u => u.UserID == user.UserID)
     .SelectMany(u => u.RegimeItems)
     .ToList();
    }

模型（cs）

 public class User
    {
        public int UserID { get; set; }
        public ICollection<RegimeItem> RegimeItems { get; set; }
        public User()
        {
            this.RegimeItems = new List<RegimeItem>();
        } 
    }
    public class RegimeItem
    {
        public int RegimeItemID { get; set; }
        public Exercise RegimeExercise { get; set; }
    }

ViewModel(cs)

public class UserExerciseViewModel
{
    public List<Exercise> AvailableExercises { get; set; }
    public List<RegimeItem> RequestedExercises { get; set; }
    public int? SelectedExercise { get; set; }
    public int[] AvailableSelected { get; set; }
    public int[] RequestedSelected { get; set; }
    public string SavedRequested { get; set; }
    public int UserID { get; set; }
}

查看（仅分段（cshtml））

<td valign="top">
   @Html.ListBoxFor(model => model.AvailableSelected, new MultiSelectList(Model.AvailableExercises, "ExerciseID", "Name", Model.AvailableSelected))
</td>
<td valign="top">
  <input type="submit" name="add"
  id="add" value=">>" /><br />
  <input type="submit" name="remove"
  id="remove" value="<<" />
</td>
<td valign="top">
    @Html.ListBoxFor(model => model.RequestedSelected, new MultiSelectList(Model.RequestedExercises, "RegimeItemID", "RegimeExercise.Name", Model.RequestedSelected))
</td>

更新：将 RemoveExercises 更改为此可修复删除问题：

void RemoveExercises(UserExerciseViewModel model, int id)
{
    var userExerciseViewModel = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
    foreach (int selected in model.RequestedSelected)
    {
        if (model.RequestedSelected != null)
        {
            User user = db.Users.Find(id);
            RegimeItem item = db.RegimeItems.Find(selected);
            item.RegimeExercise = this.GetAllExercises().FirstOrDefault(i => i.ExerciseID == selected); //--this removes the regimeexercise
            user.RegimeItems.Remove(item); //deletes the user's regimeitem
            db.RegimeItems.Remove(item); //removes the regimeitem itself 
        }
    }
    db.SaveChanges();

Answer 1

目前 AddExercises 函数从 AvailableExercises 列表框到 RequestedExercises 列表框（也 称为 RegimeItems），但它没有显示在 RequestedExercises 列表框，直到我返回页面。

不会因为你不更新模型，只更新用户/数据库。

void AddExercises(UserExerciseViewModel model, int id)
    {
        var userExerciseViewModel = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
        foreach (int selected in model.AvailableSelected)
        {
            if (model.AvailableSelected != null)
            {
                User user = db.Users.Find(id);
                user.RegimeItems.Add(new RegimeItem()
                {
                    RegimeExercise = (this.GetAllExercises().FirstOrDefault(i => i.ExerciseID == selected))
                });
            }
        }
        db.SaveChanges(); // db is updated but your model isn't
    }

但是，RemoveExercises 函数会从 RequestedExercises 列表框，但不对 数据库。

不会因为您只更新模型而不是用户。

 void RemoveExercises(UserExerciseViewModel model, int id)
    {
        var userExerciseViewModel = (UserExerciseViewModel)(Session["UserExerciseViewModel"]);
        foreach (int selected in model.RequestedSelected)
        {
            RegimeItem item = model.RequestedExercises.FirstOrDefault(i => i.RegimeItemID == selected);
            if (item != null)
            {
                model.RequestedExercises.Remove(item);
            }
        }
        db.SaveChanges(); // What is the point of this? You didn't alter the user?
    }

通常你会在这里做的是让Add和Remove这两个方法都在域对象User上工作，这样数据库就会得到适当的更新，而不是

return View(model)

您将重定向到您的 GET 操作。

   return RedirectToAction("ExerciseIndex", new { id = model2.ID, vmodel= model2 });

如果模型有您似乎没有检查的错误，您通常只会将模型返回到视图：

if (ModelState.IsValid){ ...}

还要注意如何找到用户。您在ExerciseIndex 中执行一次（无条件），然后在Remove 中再次执行。为什么不直接在ExerciseIndex 的顶部执行并传递给Remove？