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POHow to handle concurrency clash in ASP.Net MVC using post-redirect-get?
 

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  1. POHow to handle concurrency clash in ASP.Net MVC using post-redirect-get?
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    <p>I use a post-redirect-get (PRG) pattern to save an entity in ASP.Net MVC 2. The controller methods are 'Save' (inserts or updates database) and 'Edit' (retrieves user input). In 'Save', I do modification check before saving by checking a 'version' column of the entity. If someone else has modified the entity, the 'version' column will not match and I will send error message to the user.</p> <p>To maintain error messages, I use ModelState.Merge in 'Edit' method. The problem with this mechanism is that the user input is maintained and the user doesn't see the modification made by the other user. I avoid this problem by clearing ModelState before adding the concurrency clash message.</p> <p>But I feel this solution is not optimal. How would you handle concurrency clash in ASP.Net MVC?</p> <p>Here is the Edit method:</p> <pre><code> Public Function Edit() As ActionResult Dim theevent As AEvents If TempData("ModelState") IsNot Nothing And Not ModelState.Equals(TempData("ModelState")) Then ModelState.Merge(CType(TempData("ModelState"), ModelStateDictionary)) End If If RouteData.Values.ContainsKey("id") Then theevent = NHibGet.EventWithPricingsByCode(RouteData.Values("id")) Else theevent = New AEvents End If Dim InputTemplate As New EventEdit With {.EventDate = theevent.EventDate, .EventName = theevent.EventName, .IsActive = theevent.IsActive} If theevent.Template IsNot Nothing Then InputTemplate.TemplateID = theevent.Template.ID End If Dim templates As IList(Of SeatTemplates) = NHibGet.TemplatesActive ViewData("templates") = templates ViewData("eventcode") = theevent.Code ViewData("editversion") = theevent.Version Return View(InputTemplate) End Function </code></pre> <p>And the code for 'Save' is like this:</p> <pre><code> Public Function Save(ByVal id As Integer, ByVal UserData As EventEdit, ByVal EditVersion As Integer) As ActionResult Dim theevent As AEvents If id = 0 Then theevent = New AEvents Else theevent = NHibGet.EventByCode(id) End If If theevent.Version &lt;&gt; EditVersion Then ModelState.Clear() ModelState.AddModelError("", "The event is modified by someone else") Return RedirectToAction("Edit", New With {.id = id}) End If If Not ModelState.IsValid Then TempData("ModelState") = ModelState Return RedirectToAction("Edit", New With {.id = id}) End If theevent.EventDate = UserData.EventDate theevent.EventName = UserData.EventName theevent.IsActive = UserData.IsActive theevent.Template = MvcApplication.CurrentSession.Load(Of SeatTemplates)(UserData.TemplateID) Using trans As NHibernate.ITransaction = MvcApplication.CurrentSession.BeginTransaction MvcApplication.CurrentSession.SaveOrUpdate(theevent) Try trans.Commit() Catch ex As NHibernate.ADOException trans.Rollback() Throw ex End Try End Using Return RedirectToAction("Edit", New With {.id = theevent.Code}) End Function </code></pre>
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    1. PTQuestion
    1. USEndy Tjahjono
    1. USEndy Tjahjono
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    1. PO
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      1. POHow to handle concurrency clash in ASP.Net MVC using post-redirect-get?
      1. USZac
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    1. COFeels like this isn't at all ASP.NET MVC specific. Either you need to lock items for editing, or you need to allow merging items when saving, or you need to overwrite items when saving. Sounds like the merge option is what you want. Perhaps you could present the current user's now-obsolete edits in a read-only format when attempting to save an old version to allow the current user to manually merge each field?
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      1. POHow to handle concurrency clash in ASP.Net MVC using post-redirect-get?
      1. USbzlm
    2. COI'd say that my question is MVC specific because if someone would give example in PHP, it may not be translatable to MVC. But thanks for the answer.
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      1. POHow to handle concurrency clash in ASP.Net MVC using post-redirect-get?
      1. USEndy Tjahjono
 

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