Question

<HttpPost()>
    Function Edit(<Bind(Prefix:="Article")> ByVal Article As FormCollection, Optional ByVal DepartementID As Integer = 0, Optional ByVal LeverancierID As Integer = 0) As ActionResult ', ByVal ReferenceSupplierID As Integer
        ' Dim Art As Article = ArticleService.GetArticleById(Article.ArticleID)
        Dim _toUpdateArt As Article = ArticleService.GetArticleById(Article(0))
        UpdateModel(_toUpdateArt, Article)
        '  TryUpdateModel(Art, Article)
        If LeverancierID > 0 Then
            _toUpdateArt.Supplier = LeverancierService.GetLeverancierById(LeverancierID)
        Else
            _toUpdateArt.Supplier = Nothing 'HERE
            ModelState.Remove("LeverancierID")
        End If
        If DepartementID > 0 Then
            _toUpdateArt.Departement = DepartmentService.GetDepartmentByID(DepartementID)
        Else
            _toUpdateArt.Departement = Nothing 'HERE
            ModelState.Remove("DepartmentID")
        End If
        If ModelState.IsValid Then

            _toUpdateArt.EditedOn = Now
            ArticleService.SaveArticle()

            Return RedirectToAction("Index")
        Else

            ViewBag.Index = ""
            ViewBag.Create = ""
            ' ViewBag.Edit = ""
            'ViewBag.StandardValueEnabled
            ViewBag.Delete = ""
            ViewBag.Editable = ""
            '   ViewBag.LocalSearch = ""
            ViewBag.Departments = DepartmentService.GetDepartments
            ' ViewBag.StandardValueEnabled = ""

            ViewBag.MediaShow = ""
            ViewData("Media") = MediaService.GetMedia.Where(Function(el) el.Reference = Domain.Common.ReferenceTo.Article And el.ReferenceID.Equals(_toUpdateArt.ArticleID)).ToList

            Dim avw As New ViewModels.ArticleViewModel
            With avw
                .Article = _toUpdateArt
                .Leveranciers = LeverancierService.GetLeveranciers.ToList.Select(Function(dl) New SelectListItem With { _
                                                                    .Text = dl.RoepNaam, _
                                                                    .Value = dl.LeverancierID, _
                                                                    .Selected = LeverancierID = dl.LeverancierID}).ToList

                .Departements = DepartmentService.GetDepartments.Select(Function(dl) New SelectListItem With { _
                                                                            .Text = dl.Code, _
                                                                            .Value = dl.DepartmentID, _
                                                                            .Selected = DepartementID = dl.DepartmentID}).ToList

            End With


            Return View(avw)
        End If
    End Function

_toUpdateArt.Departement = Nothing and _toUpdateArt.Supplier = Nothing is to remove the optional relationship.

But it only works when i debug it and sometimes after several loops of the command, before the relation is actually removed and it’s stored in the database.

When there isn’t a breakpoint on the “function”, the Relationship will never be nulled.

Does anyone has an explanation for this and how to fix this?

Answer 1

If Department is already Nothing (null) then most likely setting it to Nothing will have no effect. I suspect you see it working in the debugger because the debugger accesses the property and causes it to lazy load. After this the property is no longer Nothing and so setting it to Nothing is detected as deleting the relationship.

There are a few ways to handle this:

• Make sure that you are mapping the FK to a property in your entity (i.e. using an FK relationship) and then set the FK to null instead of setting the navigation property to null. In this case the FK is acting as a token for the relationship such that it can be unambiguously changed without the related entity needing to be loaded.
• Always load the related entity so that the property is never null. You could do this with Include or with lazy loading.
• If you are using EF5 on .NET 4.5 then you could start using full change tracking proxies in which case setting the property to Nothing will be detected by the proxy even if it is already Nothing. Note however that there are complications with change tracking proxies and this only works for FK relationships when using .NET 4.5.