更新行时如何解决DbUpdateConcurrencyException？ [英] How to solve DbUpdateConcurrencyException when updating a row?

问题描述

我正在针对ASP.NET MVC应用程序使用实体框架代码优先方法。提交以保存更改后，编辑了一行之后，我收到了http post方法的以下错误：

I'm using the entity framework code first approach for an ASP.NET MVC application. After editing a row when submitting for saving the change I'm getting the following error for the http post method:

$类型的异常b $ b'System.Data.Entity.Infrastructure.DbUpdateConcurrencyException'
发生在EntityFramework.dll中，但未在用户代码中处理。

An exception of type 'System.Data.Entity.Infrastructure.DbUpdateConcurrencyException' occurred in EntityFramework.dll but was not handled in user code.

在db.SaveChanges（）处遇到此错误。

This error is encountered at db.SaveChanges().

db.Entry<Project>(EditedProj).State = System.Data.Entity.EntityState.Modified;
db.SaveChanges();

主代码：

[HttpGet]
public ActionResult Edit(int id)
{
    using (var db = new ProjectContext())
    {
        return View(db.Projects.Find(id));
    }
}

[HttpPost]
public ActionResult Edit(Project EditedProj)
{
    using (var db = new ProjectContext())
    {
        db.Entry<Project>(EditedProj).State = 
             System.Data.Entity.EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Projects");
    }
}

推荐答案

I找到了答案。我没有传递Http Post操作方法的id值。

I have found the answer. I was not passing id value for Http Post action method.

如本链接

由DbContext引发的异常，当预期实体的SaveChanges将导致数据库更新，但实际上数据库中没有行受到影响。

Exception thrown by DbContext when it was expected that SaveChanges for an entity would result in a database update but in fact no rows in the database were affected.

在我的情况下，上面的语句是正确的，因为我试图更新一行，但是没有id则没有行被更新。因此，例外。

In my case the above statement is true because I was trying to update a row but without id no row was updated. Hence, the exception.

可以使用包含id的隐藏输入元素来完成。下面的代码显示了如何在Edit.cshtml中进行操作–

It can be done using a hidden input element which contains the id. The code below shows how to do it in Edit.cshtml –

@using (Html.BeginForm("Edit", "Home", FormMethod.Post,
    new { @class = "form-horizontal", role = "form" }))
{
    @Html.HiddenFor(m => m.ProjectID)
    //Other code … … …
}

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