Question

I have a desktop application using vb.net, to process some excel files, those files are stored in a sql server database.
Here is the code I have:

Try
        conDCS.Open()
        comDCS.Connection = conDCS
        comDCS.CommandType = CommandType.Text
        comDCS.CommandText = "select top 2 [Filename], [File] " & _
                            "from tblFiles (nolock) " & _
                            "where ([Filename] like 'DIG%' or [Filename] like 'FAC%') and " & _
                            "(UploadDate>='" & FromDate & "' and UploadDate<'" & ToDate & "')"
        comDCS.ExecuteNonQuery()
        rdrDCS = comDCS.ExecuteReader
        If rdrDCS.HasRows Then
            While rdrDCS.Read
                Dim imageInBytes As Byte() = rdrDCS(1)
                Dim memoryStream As System.IO.MemoryStream = New System.IO.MemoryStream(imageInBytes, False)
                Dim image As System.Drawing.Image = System.Drawing.Image.FromStream(memoryStream)
                image.Save(TempPath & rdrDCS(0))
            End While
            ToProcess = True
        End If
        rdrDCS.Close()
    Catch ex As Exception
        ToProcess = False
        MessageBox.Show("Error accessing to the files: " & ex.Message)
    Finally
        conDCS.Close()
    End Try

I’m getting: “Parameter is not valid” in this line:

Dim image As System.Drawing.Image = System.Drawing.Image.FromStream(memoryStream)

I have understood that this error is related to an invalid image data, but I can’t figure it out what could be the problem.

imageInBytes has a length of 41473. And some items of the array have zero as value.

What could be wrong here, or perhaps, can anyone supply a working code to achieve this?

Answer 1

We use a common method to save a file from a database field to a file:

Public Function FieldToFile(ByVal sFileName As String, ByVal theField As Object) As Boolean
    ' Exceptions are handled by the caller

    If theField IsNot DBNull.Value Then
        Using oStream As New System.IO.FileStream(sFileName, IO.FileMode.Create, IO.FileAccess.Write)
            If oStream IsNot Nothing Then
                Dim aBytes As Byte()

                aBytes = DirectCast(theField, Byte())

                oStream.Write(aBytes, 0, aBytes.Length)
                oStream.Close()
            End If
        End Using
    End If

    Return True
End Function

This can be called as follows:

Call FieldToFile(someFileName, rdrDCS(1)