Handling concurrency access for deleting an object using Ajax.actionlink - asp.net-mvc-3

Question

i have the following view inside my asp.net MVC application that contains an ajax.actionlink for deleting objects:-
<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>
and the following post delete action method that will be called by the above ajax link:-
[HttpPost]
public void Delete(int id)
{ var a = repository.FindAnswer(id);
repository.DeleteAnswer(a);
repository.Save();}
and the folloiwng OnSuccess script:-
function deleteconfirmation3(rid, rname) {
$('#' + rid).remove();
jAlert(rname + ' Was Deleted Succsfully succsfully', 'Deletion Confirmation');}
currently if two user access the same view and then they both click on the delete link which is associated with the same object, then a null exception will be raised on one of the requests; so how i can handle this issue both on the action method side and on the view side to display a friendly message to the user; in these two cases:-
either when the var a = repository.FindAnswer(id); returns a null
exception?
Or when the repository.Save(); does not delete any record?
BR
Edit:-
i updated the post action method to the following:-
[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); }}
and on the view i update ajax.actionlink to the folloiwng:-
#{ 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"
})
and the Onsuccess script:-
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');
}
}
The above code worked fine when i test it ,, but does this approach sound acceptable as i have not written something similar to this before?
BR

Answer 1

Add a check such that if the record exists delete it or else show a message specifying that the record has already been deleted...
[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" });
}
}
apparantly you will need to change the return type from void to ActionResult or 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"
})
the success handler will be like
function myResponse(data){
if(data.IsSuccess=="True")
jAlert(data.description + ' Was Deleted Succsfully succsfully', 'Deletion Confirmation');
else {
alert("record has already been deleted");
}
}