Question

In my controller “Language” I have the following Create action method

    <HttpPost()>
    Function Create(language As Language) As ActionResult
        Try
            If ModelState.IsValid Then
                Dim name As String = language.Name
                db.Languages.Add(language)
                db.SaveChanges()
                Return RedirectToAction("Index", New System.Web.Routing.RouteValueDictionary(New With {.languageName = name, .onSuccess = ActionType.CREATE}))
            End If
        Catch ex As DataException
            ViewBag.ErrorTitle = Resources.Commands.UnableToCreate
            ViewBag.ErrorMessage = Resources.Commands.TryAgainMessage
        End Try
        Return View(language)
    End Function

How can I check if exists duplicates with the same values in the database before creating?

Answer 1

Dim Exists as Boolean = db.Languages.Any(Function (x) x.languageName = language.languageName)
If Not Exists Then
  db.Languages.Add(language)
  db.SaveChanges()
End If

forgive me, my VB is very rusty

Or implement IValidatableObject in your model that performs the check (probably a better approach):

Public Class Language
  Implements IValidatableObject

  ' Model properties

  Public Function Validate(ByVal validationContext As ValidationContext) As IEnumerable(Of ValidationResult) Implements IValidatableObject.Validate
    Dim results As List(Of ValidationResult) = New List(Of ValidationResult)

    '
    ' check if langauge already exists and assign error
    ' to results if necessary
    '

    Return results
  End Function
End Class

Link on MVC3 model validation: http://www.devproconnections.com/article/aspnetmvc/modellevel-validation-aspnet-mvc-3-136111