缺少「刪除」在MVC POST方法的東西（EF 4.1）

Question

根據本例.. http://msdn.microsoft.com/en-us/data/gg685489

我正在與刪除功能的問題。

[HttpPost] 
public ActionResult Delete(int id, Blog blog) 
{ 
    try 
    { 
     using (var db = new BlogDataEntities()) 
     { 
      //Having issue here.. as soon as the next line is run in debug 
      //mode .. it goes to catch.. and returns a view with null values. 

      db.Entry(blog).State = System.Data.EntityState.Deleted; 
      db.SaveChanges(); 
     } 
     return RedirectToAction("Index"); 
    } 
    catch 
    { 
     return View(); 
    } 
} 

在參數我檢查'博客'沒有得到需要刪除的實際博客模型。所有其他方法做工精細（編輯，刪除（獲取）。等等。 但刪除後失敗我缺少的東西在此先感謝您的幫助

編輯：？

視圖代碼

@model DBFirstMVC.Models.Blog 

@{ 
ViewBag.Title = "Delete"; 
} 

    <h2>Delete</h2> 

<h3>Are you sure you want to delete this?</h3> 
<fieldset> 
<legend>Blog</legend> 

<div class="display-label">Title</div> 
<div class="display-field">@Model.Title</div> 

<div class="display-label">BloggerName</div> 
<div class="display-field">@Model.BloggerName</div> 
</fieldset> 
@using (Html.BeginForm()) { 
    <p> 
    <input type="submit" value="Delete" /> | 
    @Html.ActionLink("Back to List", "Index") 
    </p> 
} 

編輯2： 非剃刀代碼鑑於：

<% using (Html.BeginForm()) { %> 
<p> 
    <input type="submit" value="Delete" /> | 
    <%: Html.ActionLink("Back to List", "Index") %> 
</p> 
<% } %> 

EDIT 3：（我試圖在C++）

<% using (Html.BeginForm()) { %> 
<p> 

    <%=Html.DisplayForModel();%> //Tried Html.EditorForModel also.. 
    <input type="submit" value="Delete" /> | 
    <%: Html.ActionLink("Back to List", "Index") %> 
</p> 
<% } %> 

最後編輯（修正方案）

@model DBFirstMVC.Models.Blog 

@{ 
ViewBag.Title = "Delete"; 
} 

<h2>Delete</h2> 

<h3>Are you sure you want to delete this?</h3> 

@using (Html.BeginForm()) { 
<p> 
<fieldset> 
<legend>Blog</legend> 

<div class="display-label">Title</div> 
<div class="display-field">@Model.Title</div> 

<div class="display-label">BloggerName</div> 
<div class="display-field">@Model.BloggerName</div> 

    <input type="submit" value="Delete" /> | 
@Html.ActionLink("Back to List", "Index") 
</fieldset> 
</p> 
} 

Answer 1

上下文可能沒有您的博客條目，因爲它沒有附加到上下文。

你可能需要先檢索博客，然後將其標記爲使用Entry方法刪除：

[HttpPost] 
public ActionResult Delete(int id, Blog blog) 
{ 
    try 
    { 
     using (var db = new BlogDataEntities()) 
     { 
      // retrieve the blog from the database 
      var realBlog = db.Blogs.Find(blog.Id); 

      // nothing to do here, just redirect 
      if(realBlog == null) 
       return RedirectToAction("Index"); 

      // since you have the entity just do this instead: 
      db.Blogs.Remove(realBlog); 
      db.SaveChanges(); 
     } 

     return RedirectToAction("Index"); 
    } 
    catch(Exception) 
    { 
     return View(); 
    } 
} 

我真的不使用你的實體作爲你的模型雖然的想法一致。您應該使用視圖模型。

編輯

既然你現在說博客沒有被通過，試試這個：

@model Blog 

@using (Html.BeginForm()) 
{ 
    @Html.EditorForModel() 

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

你實際上沒有給模型綁定任何它所需的細節構建你的模型。

Answer 2

是可以嘗試以下方法：

[HttpPost] 
public ActionResult Delete(Blog deletedBlog) 
{ 
    try 
    { 
     using (var db = new BlogDataEntities()) 
     { 
      // get blog entry from db context!! 
      Blog blog = db.Blogs.Find(deletedBlog.Id); 
      //Having issue here.. as soon as the next line is run in debug 
      //mode .. it goes to catch.. and returns a view with null values. 

      db.Entry(blog).State = System.Data.EntityState.Deleted; 
      db.SaveChanges(); 
     } 
     return RedirectToAction("Index"); 
    } 
    catch(Exception e) 
    { 
     // should catch more specific exception 
     // but catching 'e' should be a start 
     return View(); 
    } 
} 

[更新] - 通過從您的博客模式正如Dismissile所說，你應該真正使用視圖模型，而不是實體模型是目的。

另外，您應該捕獲內部異常消息並檢查以獲取更多線索。

Answer 3

Delete中的blog參數Action最可能是null，因爲您只發布博客的ID，而不是整個博客對象。我會修改刪除操作以僅接受id（根據Dismissile的答案），或者修改刪除視圖以發佈整個博客對象並從操作中刪除該id（因爲它屬於博客對象）：

[HttpPost] 
public ActionResult Delete(Blog blog) 
{ 
    try 
    { 
     using (var db = new BlogDataEntities()) 
     { 
      db.Entry(blog).State = System.Data.EntityState.Deleted; 
      db.SaveChanges(); 
     } 
     return RedirectToAction("Index"); 
    } 
    catch 
    { 
     return View(); 
    } 
} 

Answer 4

我在一些評論中發佈了這個，但我覺得它值得單獨回答一個「替代」。

您的控制器應該很苗條，並儘可能地堅持到single responsibility principle。

BlogController

public class BlogController : Controller 
{ 
    private BlogService blogService; 

    public BlogService() 
    { 
     blogService = new BlogService(); 
    } 

    [HttpPost] 
    public ActionResult Delete(int id) 
    { 

     // make sure the user has permission to delete before actually deleting 

     // now that we know the user has permission 
     if (blogService.Delete(id)) 
     { 
      return RedirectToAction("Index"); 
     } 
     else 
     { 
      return View(); 
     } 
    } 
} 

現在你必須附着在single responsibility principle一個可重用的服務層。

BlogService

public class BlogService 
{ 

    private BlogDataEntities dc; 

    public BlogService() 
    { 
     dc = new BlogDataEntities(); 
    } 

    public bool Delete(int Id) 
    { 
     try 
     { 
      var blog= (from b in dc.Blogs where Blog.ID == Id select b).First(); 

      // blog doesn't exist, exit and return false. 
      if(blog == null) 
       return false; 

      // blog exists, remove it 
      dc.Blogs.Remove(blog); 

      // push the delete to the database 
      SaveChanges(); 

      // it worked, return true. 
      return true; 
     } 
     catch(System.Exception ex) 
     { 
      // an error happened, handle it and return false. 
      return false; 
     } 
    } 

    // I like to keep my `SubmitChanges()` Separate in case I need to 
    // stack up a few processes before hitting the database. 
    public void SaveChanges() 
    { 
     dc.SaveChanges(); 
    } 
}