使用 Ajax.actionlink 处理删除对象的并发访问

Question

我的 asp.net MVC 应用程序中有以下视图，其中包含用于删除对象的 ajax.actionlink：-

<table id="incrementanswer">
    <tr>
        <th>
            Description
        </th>
        <th>
            Answer 
        </th>
        <th></th>
    </tr>

@foreach (var answer in Model.Answers.OrderBy(a => a.IsRight))
{
       <tr id =  @answer.AnswersID>

        <td>
            @Html.DisplayFor(modelItem => answer.Description)
        </td>
        <td>
            @Html.DisplayFor(modelItem => answer.Answer_Description.description)
        </td>
        <td>

       @{ string i = "Are uou sure you want to delete " + @answer.Description.ToString() + " ?";}
         @Ajax.ActionLink("Delete", "Delete", "Answer",
        new { id = answer.AnswersID },
          new AjaxOptions
          {
              Confirm = i,
              HttpMethod = "Post",
              OnBegin = string.Format(
                       "disablelink({0})",
                       Json.Encode(answer.AnswersID)),
              OnSuccess = string.Format(
                        "deleteconfirmation3({0},{1})",
                        Json.Encode(answer.AnswersID), Json.Encode(answer.Description))
          })  </td>
        </tr>}</table>

以及将由上述 ajax 链接调用的以下 post delete 操作方法：-

[HttpPost] 
        public void Delete(int id) 
        {       var a = repository.FindAnswer(id); 
                repository.DeleteAnswer(a); 
                repository.Save();} 

以及以下 OnSuccess 脚本：-

function deleteconfirmation3(rid, rname) {
    $('#' + rid).remove();
    jAlert(rname + ' Was Deleted Succsfully succsfully', 'Deletion Confirmation');}

目前，如果两个用户访问同一个视图，然后他们都点击了与同一个对象关联的删除链接，那么其中一个请求将引发空异常；那么我如何在操作方法端和视图端处理这个问题以向用户显示友好的消息；在这两种情况下：-

1. var a = repository.FindAnswer(id); 返回 null 例外？
2. 或者repository.Save();没有删除任何记录？

BR

编辑：-

我将发布操作方法更新为以下内容：-

[HttpPost]
    public ActionResult Delete(int id)
    {

        try
        {
            Thread.Sleep(1000);
            var a = repository.FindAnswer(id);

            repository.DeleteAnswer(a);
            repository.Save();
            return Json(new { IsSuccess = "True", id = id, description = a.Description }, JsonRequestBehavior.AllowGet); 
        }
        catch (ArgumentNullException) {
            return Json(new { IsSuccess = "False" }, JsonRequestBehavior.AllowGet);  }}

在视图上我将 ajax.actionlink 更新为以下内容：-

@{ string i = "Are uou sure you want to delete " + @answer.Description.ToString() + " ?";}
         @Ajax.ActionLink("Delete", "Delete", "Answer",
        new { id = answer.AnswersID },
          new AjaxOptions
          {
              //OnBegin = "deleteconfirmation1",
              Confirm = i,
              HttpMethod = "Post",
              OnBegin = string.Format(
                       "disablelink({0})",
                       Json.Encode(answer.AnswersID)),

              OnSuccess =  "myresponse" 
        })

和 Onsuccess 脚本：-

    function myresponse(data) {
    if (data.IsSuccess == "True") 
    {
        $('#' + data.id ).remove();
        jAlert(data.description + ' Was Deleted Succsfully succsfully', 'Deletion Confirmation');
    }
    else {
        $('#' + data.id).remove();
        jAlert(data.description + 'record has already been deleted', 'aaaa');
    } 
}

上面的代码在我测试时运行良好，但是这种方法听起来可以接受吗，因为我以前没有写过类似的东西？ BR

Answer 1

添加一个检查，如果记录存在则删除它，否则显示一条消息，指出记录已被删除...

[HttpPost] 
public ActionResult Delete(int id) 
{       var a = repository.FindAnswer(id); 
        if(/*check if a is not null*/){
        repository.DeleteAnswer(a); 
        repository.Save();
        return Json(new{ IsSuccess="True", id=id,description=a.Description });
        }else{
            // display a message record already been deleted
          return Json(new{ IsSuccess="False" });
       }     

 } 

显然，您需要将返回类型从 void 更改为 ActionResult 或 JsonResult

@Ajax.ActionLink("Delete", "Delete", "Answer",
        new { id = answer.AnswersID },
          new AjaxOptions
          {
              Confirm = i,
              HttpMethod = "Post",
              OnBegin = string.Format(
                       "disablelink({0})",
                       Json.Encode(answer.AnswersID)),
              OnSuccess = "myResponse"
          })

成功的处理程序会像

function myResponse(data){
 if(data.IsSuccess=="True")
   jAlert(data.description + ' Was Deleted Succsfully succsfully', 'Deletion Confirmation');
  else {
   alert("record has already been deleted");
  }

}