mvc4 dropdownList插入NULL

Question

我在這里搜索了很多東西，找到了類似的東西作為下拉列表
這是我的模型：

public class Profits
    {
        [Key]
        public int Id { get; set; }
        public double Value { get; set; }
        public string Description{ get; set; }
       [DataType(DataType.Date)]
        public DateTime DateInput { get; set; }
        public UserProfile User { get; set; }
        public Categories CategoryName { get; set; }//foreign key
          public   int CategoryID { get; set; }
    }

 public class Categories
    {
        [Key]
        public int Id { get; set; }
        [Required]
        public string  Name { get; set; }
        public UserProfile User { get; set; }


    }

這是我的控制器：這會將我的數據傳遞給dropDownList ...

public ActionResult Create()
{
    var dba = new WHFMDBContext();
    var query = dba.Categories.Select(c => new { c.Id, c.Name });
    ViewBag.Id = new SelectList(query.AsEnumerable(), "Id", "Name", 3);
    return View();
}

[HttpPost]
        [InitializeSimpleMembership]
        public ActionResult Create(Profits profits)
        {
            var user = db.UserProfiles.FirstOrDefault(x => x.UserId == WebSecurity.CurrentUserId);
            var profit = new Profits
            {
               Value= profits.Value,
               Description = profits.Description,
               DateInput =profits.DateInput,
               CategoryName =profits.CategoryName,// ???
                User = user,

            };
            db.Profits.Add(profit);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

我的觀點 ：

@model WebHFM.Models.Profits



@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>Profits</legend>


    <div class="editor-field">
     @Html.LabelFor(model => model.CategoryName)
        </div>
    <div class="editor-field">
         @Html.DropDownList("Id", (SelectList) ViewBag.Id, "--Select One--") 
        @Html.ValidationMessageFor(model => model.CategoryName)
    </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Value)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Value)
            @Html.ValidationMessageFor(model => model.Value)
        </div>...

這將數據插入數據庫，但是CategoryName_Id為NULL我缺少什么？ 和CategoryName = profits.CategoryName這是Profits public Categories CategoryName { get; set; }的外鍵public Categories CategoryName { get; set; } public Categories CategoryName { get; set; }

Answer 1

修改您的利潤類別，添加以下內容：

Profits
{
  int CategoryID {get;set;}
}

修改您的cshtml。 更改

@Html.DropDownList("Id", (SelectList) ViewBag.Id, "--Select One--") 

至

@Html.DropDownList("CategoryID", (SelectList) ViewBag.Id, "--Select One--") 

更改您的控制器：

public ActionResult Create(Profits profits)
        {
            var user = db.UserProfiles.FirstOrDefault(x => x.UserId == WebSecurity.CurrentUserId);
            var category = db.Categories.FirstOrDefault(o => o.CategoryId == profits.CategoryID);
            var profit = new Profits
            {
               Value= profits.Value,
               Description = profits.Description,
               DateInput =profits.DateInput,
               CategoryName = category,
               User = user
            };
            db.Profits.Add(profit);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

這將更改您的下拉列表以返回所選的CategoryID。 標記如下所示：

<select name="CategoryID" />

在您的回發上，這將綁定到新的Profits.CategoryID。 然后，您可以使用該查詢進行數據庫查詢，以獲取選定的類別對象，然后將其分配給Profits.CategoryName。

Answer 2

您的Create（）動作返回return View(); 沒有將模型傳遞給視圖方法參數。

Answer 3

這是我不看您的模型所建議的。 PopulateCategoriesDropDownList與您的create動作位於同一控制器中

private void PopulateCategoriesDropDownList(object selectedCategories = null)
    {
        var categoriesQuery = from d in _dataSource.Categories
                         orderby d.Name
                         select d;
        ViewBag.CategoryId= new SelectList(categoriesQuery, "CategoryId", "Name", selectedCategories);
    }

然后你的動作是這樣的。

    [HttpGet]
    public ActionResult Create()
    {
      PopulateCategoriesDropDownList();
    return View();
   }


    [HttpPost]
    [InitializeSimpleMembership]
    public ActionResult Create(Profits profits)
    {
         var user = db.UserProfiles.FirstOrDefault(x => x.UserId ==       WebSecurity.CurrentUserId);
        var profit = new Profits
        {
           Value= profits.Value,
           Description = profits.Description,
           DateInput =profits.DateInput,
           CategoryName =profits.CategoryName,// ???
            User = user,

        };
        db.Profits.Add(profit);
        db.SaveChanges();
        PopulateCategoriesDropDownList(profit.CategoryId);
       return View(profit);
    }

在您看來：

<div class="editor-label">
            @Html.LabelFor(model => model.CategoryId, "Pick Category")
    </div>
    <div class="editor-field">
        @Html.DropDownList("CategoryId", String.Empty)
        @Html.ValidationMessageFor(model => model.CategoryId)
    </div><br/>