ACC: Reading, Storing, & Writing Binary Large Objects (BLOBs)

      '**************************************************************
      ' FUNCTION: ReadBLOB()
      '
      ' PURPOSE:
      '   Reads a BLOB from a disk file and stores the contents in the
      '   specified table and field.
      '
      ' PREREQUISITES:
      '   The specified table with the OLE object field to contain the
      '   binary data must be opened in Visual Basic code (Access Basic
      '   code in Microsoft Access 2.0 and earlier) and the correct record
      '   navigated to prior to calling the ReadBLOB() function.
      '
      ' ARGUMENTS:
      '   Source - The path and filename of the binary information
      '            to be read and stored.
      '   T      - The table object to store the data in.
      '   Field  - The OLE object field in table T to store the data in.
      '
      ' RETURN:
      '   The number of bytes read from the Source file.
      '**************************************************************
      Function ReadBLOB(Source As String, T As Recordset, _
      sField As String)
          Dim NumBlocks As Integer, SourceFile As Integer, i As Integer
          Dim FileLength As Long, LeftOver As Long
          Dim FileData As String
          Dim RetVal As Variant

          On Error GoTo Err_ReadBLOB

          ' Open the source file.
          SourceFile = FreeFile
          Open Source For Binary Access Read As SourceFile

          ' Get the length of the file.
          FileLength = LOF(SourceFile)
          If FileLength = 0 Then
              ReadBLOB = 0
              Exit Function
          End If

          ' Calculate the number of blocks to read and leftover bytes.
          NumBlocks = FileLength \ BlockSize
          LeftOver = FileLength Mod BlockSize

          ' SysCmd is used to manipulate status bar meter.
          RetVal = SysCmd(acSysCmdInitMeter, "Reading BLOB", _
                   FileLength \ 1000)

          ' Put the record in edit mode.
          T.Edit

          ' Read the leftover data, writing it to the table.
          FileData = String$(LeftOver, 32)
          Get SourceFile, , FileData
          T(sField).AppendChunk (FileData)

          RetVal = SysCmd(acSysCmdUpdateMeter, LeftOver / 1000)

          ' Read the remaining blocks of data, writing them to the table.
          FileData = String$(BlockSize, 32)
          For i = 1 To NumBlocks
              Get SourceFile, , FileData
              T(sField).AppendChunk (FileData)

              RetVal = SysCmd(acSysCmdUpdateMeter, BlockSize * i / 1000)
          Next i

          ' Update the record and terminate function.
          T.Update
          RetVal = SysCmd(acSysCmdRemoveMeter)
          Close SourceFile
          ReadBLOB = FileLength
          Exit Function

      Err_ReadBLOB:
          ReadBLOB = -Err
          Exit Function

      End Function

      '**************************************************************
      ' FUNCTION: WriteBLOB()
      '
      ' PURPOSE:
      '   Writes BLOB information stored in the specified table and field
      '   to the specified disk file.
      '
      ' PREREQUISITES:
      '   The specified table with the OLE object field containing the
      '   binary data must be opened in Visual Basic code (Access Basic
      '   code in Microsoft Access 2.0 or earlier) and the correct
      '   record navigated to prior to calling the WriteBLOB() function.
      '
      ' ARGUMENTS:
      '   T           - The table object containing the binary information.
      '   sField      - The OLE object field in table T containing the
      '                 binary information to write.
      '   Destination - The path and filename to write the binary
      '                 information to.
      '
      ' RETURN:
      '   The number of bytes written to the destination file.
      '**************************************************************
      Function WriteBLOB(T As Recordset, sField As String, _
      Destination As String)
          Dim NumBlocks As Integer, DestFile As Integer, i As Integer
          Dim FileLength As Long, LeftOver As Long
          Dim FileData As String
          Dim RetVal As Variant

          On Error GoTo Err_WriteBLOB

          ' Get the size of the field.
          FileLength = T(sField).FieldSize()
          If FileLength = 0 Then
              WriteBLOB = 0
              Exit Function
          End If

          ' Calculate number of blocks to write and leftover bytes.
          NumBlocks = FileLength \ BlockSize
          LeftOver = FileLength Mod BlockSize

          ' Remove any existing destination file.
          DestFile = FreeFile
          Open Destination For Output As DestFile
          Close DestFile

          ' Open the destination file.
          Open Destination For Binary As DestFile

          ' SysCmd is used to manipulate the status bar meter.
          RetVal = SysCmd(acSysCmdInitMeter, _
          "Writing BLOB", FileLength / 1000)

          ' Write the leftover data to the output file.
          FileData = T(sField).GetChunk(0, LeftOver)
          Put DestFile, , FileData

          ' Update the status bar meter.
          RetVal = SysCmd(acSysCmdUpdateMeter, LeftOver / 1000)

          ' Write the remaining blocks of data to the output file.
          For i = 1 To NumBlocks
              ' Reads a chunk and writes it to output file.
              FileData = T(sField).GetChunk((i - 1) * BlockSize _
                 + LeftOver, BlockSize)
              Put DestFile, , FileData

              RetVal = SysCmd(acSysCmdUpdateMeter, _
              ((i - 1) * BlockSize + LeftOver) / 1000)
          Next i

          ' Terminates function
          RetVal = SysCmd(acSysCmdRemoveMeter)
          Close DestFile
          WriteBLOB = FileLength
          Exit Function

      Err_WriteBLOB:
          WriteBLOB = -Err
          Exit Function

      End Function

      '**************************************************************
      ' SUB: CopyFile
      '
      ' PURPOSE:
      '   Demonstrates how to use ReadBLOB() and WriteBLOB().
      '
      ' PREREQUISITES:
      '   A table called BLOB that contains an OLE Object field called
      '   Blob.
      '
      ' ARGUMENTS:
      '   Source - The path and filename of the information to copy.
      '   Destination - The path and filename of the file to write
      '                 the binary information to.
      '
      ' EXAMPLE:
      '   CopyFile "c:\windows\winfile.hlp", "c:\windows\winfil_1.hlp"
      '**************************************************************
      Sub CopyFile(Source As String, Destination As String)
          Dim BytesRead As Variant, BytesWritten As Variant
          Dim Msg As String
          Dim db As Database
          Dim T As Recordset

          ' Open the BLOB table.
          Set db = CurrentDb()
          Set T = db.OpenRecordset("BLOB", dbOpenTable)

          ' Create a new record and move to it.
          T.AddNew
          T.Update
          T.MoveLast

          BytesRead = ReadBLOB(Source, T, "Blob")

          Msg = "Finished reading """ & Source & """"
          Msg = Msg & Chr$(13) & ".. " & BytesRead & " bytes read."
          MsgBox Msg, 64, "Copy File"

          BytesWritten = WriteBLOB(T, "Blob", Destination)

          Msg = "Finished writing """ & Destination & """"
          Msg = Msg & Chr$(13) & ".. " & BytesWritten & " bytes written."
          MsgBox Msg, 64, "Copy File"
      End Sub