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In my datacontext, CalcinerDataContext, I have a class, MainData, and a simply inherited class, NewSample (used just to explore this error). The code below runs without any errors:

        Dim cdc As New CalcinerDataAccess.CalcinerDataContext
        Dim newData As New CalcinerDataAccess.MainData
        With newData
            .LotNumber = "Test1"
            .ProcessType = 4
            .SubmitterID = 2
            .Calciner = 1
            .DateEntered = Now
        End With

        Try
            cdc.MainDatas.InsertOnSubmit(newData)

        Catch ex As Exception
            Debug.WriteLine(ex.ToString)
            MsgBox(ex.Message)
        End Try

The code below generates the following error: System.NullReferenceException: Object reference not set to an instance of an object. at System.Data.Linq.Table`1.InsertOnSubmit(TEntity entity). Note that the only difference between these two code blocks is the instantiation of newData

        Dim cdc As New CalcinerDataAccess.CalcinerDataContext
        Dim newData As New CalcinerDataAccess.NewSample
        With newData
            .LotNumber = "Test1"
            .ProcessType = 4
            .SubmitterID = 2
            .Calciner = 1
            .DateEntered = Now
        End With

        Try
            cdc.MainDatas.InsertOnSubmit(newData)

        Catch ex As Exception
            Debug.WriteLine(ex.ToString)
            MsgBox(ex.Message)
        End Try

Why does the inherited class throw an exception, but the base class does not?

blueshift
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  • It appears that both code samples are identical. Please review and resubmit. – Jim Wooley Mar 21 '11 at 14:18
  • In the second code set, newData is an instance of NewSample, not MainData. NewSample inherits from MainData. In the datacontext designer, I simply added a class, NewSample, and then added an inheritance connector from MainData to NewSample. I did not add any properties or methods to NewSample. – blueshift Mar 21 '11 at 19:53

0 Answers0