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Title | Save and restore pictures in a database using ADO with AppendChunk and GetChunk |
Keywords | database, AppendChunk, GetChunk |
Categories | Database, Graphics |
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To add a new record, the program lets the user select a graphic file. The program opens the file and reads it in blocks of binary data. For each block, the program uses AppendChunk to add the block to the database
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Private Sub mnuRecordAdd_Click()
Dim rs As ADODB.Recordset
Dim person_name As String
Dim file_num As String
Dim file_length As String
Dim bytes() As Byte
Dim num_blocks As Long
Dim left_over As Long
Dim block_num As Long
person_name = InputBox("Name")
If Len(person_name) = 0 Then Exit Sub
dlgPicture.Flags = _
cdlOFNFileMustExist Or _
cdlOFNHideReadOnly Or _
cdlOFNExplorer
dlgPicture.CancelError = True
dlgPicture.Filter = "Graphics " & _
"Files|*.bmp;*.ico;*.jpg;*.gif"
On Error Resume Next
dlgPicture.ShowOpen
If Err.Number = cdlCancel Then
Exit Sub
ElseIf Err.Number <> 0 Then
MsgBox "Error " & Format$(Err.Number) & _
" selecting file." & vbCrLf & Err.Description
Exit Sub
End If
' Open the picture file.
file_num = FreeFile
Open dlgPicture.FileName For Binary Access Read As _
#file_num
file_length = LOF(file_num)
If file_length > 0 Then
num_blocks = file_length / BLOCK_SIZE
left_over = file_length Mod BLOCK_SIZE
Set rs = New ADODB.Recordset
rs.CursorType = adOpenKeyset
rs.LockType = adLockOptimistic
rs.Open "Select Name, Picture, FileLength FROM " & _
"People", m_DBConn
rs.AddNew
rs!Name = person_name
rs!FileLength = file_length
ReDim bytes(BLOCK_SIZE)
For block_num = 1 To num_blocks
Get #file_num, , bytes()
rs!Picture.AppendChunk bytes()
Next block_num
If left_over > 0 Then
ReDim bytes(left_over)
Get #file_num, , bytes()
rs!Picture.AppendChunk bytes()
End If
rs.Update
Close #file_num
lstPeople.AddItem person_name
lstPeople.Text = person_name
End If
End Sub
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To retreive a picture, the program selects the appropriate database record. It uses the TemporaryFileName function to get a temporary file name and opens the file. It then uses GetChunk to read the data from the database in blocks and writes the blocks into the file. The program then uses LoadPicture to load the file, and Kill to remove it.
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' Display the clicked person.
Private Sub lstPeople_Click()
Dim rs As ADODB.Recordset
Dim bytes() As Byte
Dim file_name As String
Dim file_num As Integer
Dim file_length As Long
Dim num_blocks As Long
Dim left_over As Long
Dim block_num As Long
Dim hgt As Single
picPerson.Visible = False
Screen.MousePointer = vbHourglass
DoEvents
' Get the record.
Set rs = m_DBConn.Execute("SELECT * FROM People WHERE " & _
"Name='" & _
lstPeople.Text & "'", , adCmdText)
If rs.EOF Then Exit Sub
' Get a temporary file name.
file_name = TemporaryFileName()
' Open the file.
file_num = FreeFile
Open file_name For Binary As #file_num
' Copy the data into the file.
file_length = rs!FileLength
num_blocks = file_length / BLOCK_SIZE
left_over = file_length Mod BLOCK_SIZE
For block_num = 1 To num_blocks
bytes() = rs!Picture.GetChunk(BLOCK_SIZE)
Put #file_num, , bytes()
Next block_num
If left_over > 0 Then
bytes() = rs!Picture.GetChunk(left_over)
Put #file_num, , bytes()
End If
Close #file_num
' Display the picture file.
picPerson.Picture = LoadPicture(file_name)
picPerson.Visible = True
Width = picPerson.Left + picPerson.Width + Width - _
ScaleWidth
hgt = picPerson.Top + picPerson.Height + Height - _
ScaleHeight
If hgt < 1440 Then hgt = 1440
Height = hgt
Kill file_name
Screen.MousePointer = vbDefault
End Sub
' Return a temporary file name.
Private Function TemporaryFileName() As String
Dim temp_path As String
Dim temp_file As String
Dim length As Long
' Get the temporary file path.
temp_path = Space$(MAX_PATH)
length = GetTempPath(MAX_PATH, temp_path)
temp_path = Left$(temp_path, length)
' Get the file name.
temp_file = Space$(MAX_PATH)
GetTempFileName temp_path, "per", 0, temp_file
TemporaryFileName = Left$(temp_file, InStr(temp_file, _
Chr$(0)) - 1)
End Function
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You could use a similar technique to save and restore other types of files. For example, you could restore an executable program and then execute it.
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