缺少“删除”在MVC POST方法的东西（EF 4.1）

Question

根据本例.. http://msdn.microsoft.com/en-us/data/gg685489

我正在与删除功能的问题。

[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(); 
    } 
} 

在参数我检查'博客'没有得到需要删除的实际博客模型。所有其他方法做工精细（编辑，删除（获取）。等等。 但删除后失败我缺少的东西在此先感谢您的帮助

编辑：？

视图代码

@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> 
} 

编辑2： 非剃刀代码鉴于：

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

EDIT 3：（我试图在C++）

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

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

最后编辑（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

上下文可能没有您的博客条目，因为它没有附加到上下文。

你可能需要先检索博客，然后将其标记为使用Entry方法删除：

[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(); 
    } 
} 

我真的不使用你的实体作为你的模型虽然的想法一致。您应该使用视图模型。

编辑

既然你现在说博客没有被通过，试试这个：

@model Blog 

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

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

你实际上没有给模型绑定任何它所需的细节构建你的模型。

Answer 2

是可以尝试以下方法：

[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] - 通过从您的博客模式正如Dismissile所说，你应该真正使用视图模型，而不是实体模型是目的。

另外，您应该捕获内部异常消息并检查以获取更多线索。

Answer 3

Delete中的blog参数Action最可能是null，因为您只发布博客的ID，而不是整个博客对象。我会修改删除操作以仅接受id（根据Dismissile的答案），或者修改删除视图以发布整个博客对象并从操作中删除该id（因为它属于博客对象）：

[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

我在一些评论中发布了这个，但我觉得它值得单独回答一个“替代”。

您的控制器应该很苗条，并尽可能地坚持到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(); 
     } 
    } 
} 

现在你必须附着在single responsibility principle一个可重用的服务层。

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(); 
    } 
}