Question

遵循此示例.. http://msdn.microsoft.com/en-us/data/gg685489

我遇到了删除功能的问题。

[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();
    }
}

在我检查的参数'blog'中没有得到需要删除的实际博客模型。所有其他方法都可以正常工作（编辑，删除（获取）..等等.. 但删除帖子失败。我错过了什么吗？提前感谢您的帮助。

编辑：

查看代码

@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：

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

编辑3 :(我在aspx中尝试过）

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

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

最终编辑（更正解决方案）

@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

上下文可能没有您博客的条目，因为它没有附加到上下文。

您可能需要首先检索博客，然后使用Entry方法将其标记为已删除：

[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();
    }
}

我不同意将您的实体用作模型的想法。您应该使用View Models。

修改

由于您现在说博客没有通过，请尝试以下方法：

@model Blog @using ( Html.BeginForm() ) { @Html.EditorForModel() <input type="submit" value="Delete" /> }

您实际上并没有给模型绑定器提供构建模型所需的任何细节。

Answer 2

是否可以尝试以下方法：

[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] - 从视图中传入您的Blog模型，因为Dismissile说，您应该真正使用视图模型，而不是实体模型。

此外，您应该捕获内部异常消息并检查以获取更多线索。

Answer 3

blog操作中的Delete参数最有可能为空，因为您只发布博客的ID，而不是整个博客对象。我要么修改删除操作以仅接受id（根据Dismissile的答案），要么修改删除视图以发布整个博客对象并从Action中删除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帖子，但我认为这对于“替代方案”应该是一个单独的答案。

您的控制器应该很苗条，并尽可能地遵守single responsibility principle。

<强> 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，您将拥有一个符合single responsibility principle。

的可重复使用服务图层

<强> 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();
    }  
}

在MVC中删除“删除”post方法中的内容（EF 4.1）

4 个答案: