Mysql Ms Access Import Data Transfer

Importing OLE Objects from Access to MySQL: A Comprehensive Guide

Transferring data from one database system to another can be a challenging task—especially when dealing with complex data types like OLE Objects, which are often used for images in Microsoft Access. If you’ve encountered issues trying to import tables with OLE objects into MySQL, you’re not alone. Many users have faced similar challenges, including corrupted images or failed imports. This blog post will walk you through an effective method to tackle this problem and ensure a successful transfer.

Understanding the Problem

When importing tables from Access to MySQL, especially those containing images stored as OLE Objects, users often experience:

  • Images not transferring properly: Tools like the MySQL migration tool may not handle OLE Objects well, leaving the fields blank.
  • Corrupted images: Even when data is imported, the images may appear as binary data, indicating they’re improperly formatted or corrupted.

To overcome these issues, a targeted approach is necessary to extract the actual image data from OLE serialization.

The Solution: Extracting Images from OLE Objects

The solution involves the development of a small code snippet that helps extract the images from the Access database table. We will use a function named GetImageFromRow, which will process a DataRowView containing one row of data from the Access table.

Step 1: Writing the Code

Here’s a detailed breakdown of the function:

Private Function GetImageFromRow(ByRef row As DataRowView, ByVal columnName As String) As Bitmap
    Dim oImage As Bitmap = New Bitmap("c:\default.jpg")
    Try
        If Not IsDBNull(row(columnName)) Then
            If row(columnName) IsNot Nothing Then
                Dim mStream As New System.IO.MemoryStream(CType(row(columnName), Byte()))
                If mStream.Length > 0 Then

                    Dim b(Convert.ToInt32(mStream.Length - 1)) As Byte
                    mStream.Read(b, 0, Convert.ToInt32(mStream.Length - 1))

                    Dim position As Integer = 0

                    For index As Integer = 0 To b.Length - 3
                        If b(index) = &HFF And b(index + 1) = &HD8 And b(index + 2) = &HFF Then
                            position = index
                            Exit For
                        End If
                    Next

                    If position > 0 Then
                        Dim jpgStream As New System.IO.MemoryStream(b, position, b.Length - position)
                        oImage = New Bitmap(jpgStream)
                    End If
                End If
            End If
        End If
    Catch ex As Exception
        Throw New ApplicationException(ex.Message, ex)
    End Try
    Return oImage
End Function

Step 2: How the Code Works

  1. Initialization: A new bitmap object is initialized. This acts as a placeholder in case the image extraction fails.

  2. Data Extraction: The function checks if the specified column contains any data. If there is a valid OLE Object, the byte array is extracted.

  3. Identifying Valid JPEG Data:

    • The function looks for the JPEG file signature in the byte array, denoted by the sequence FF D8 FF.
    • Once found, it marks the position to slice the byte array accurately and create a new memory stream specifically for the image.

  4. Bitmap Creation: Finally, a bitmap object is created from this new memory stream containing only the image data, and the function returns it.

Step 3: Updating MySQL

Once you’ve extracted the bitmap from each row in the Access table, you’ll then need to update the corresponding entry in MySQL. This can typically be done with a straightforward SQL UPDATE command with the bitmap’s data stored in a MediumBlob field.

Notes for Improvement

  • The presented method is a straightforward hack useful for one-time transfers. However, it may benefit from additional refinement.
  • Consider exploring APIs that might simplify the image extraction, enhancing reliability and performance during transfers.

Conclusion

Moving OLE Objects from Access to MySQL does not have to be a daunting task. By implementing this code snippet to extract images cleanly, you can avoid upsetting data integrity issues and ensure a smooth migration. Remember to test the process thoroughly to confirm that images are appearing correctly in your MySQL database.

Happy coding, and may your data transfers be seamless!