AppendChunk and GetChunk Methods Example (ADO)


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AppendChunk and GetChunk Methods Example

This example uses the AppendChunk and GetChunk methods to fill an image field with data from another record, 32K at a time. In a real application, one might use a procedure like this to copy a record containing a photo or graphic image field from one table to another. In this example, the record is simply being copied back to same table. Note that all the chunk manipulation takes place within a single AddNew-Update sequence.

Public Sub AppendChunkX()

	Dim cnn1 As ADODB.Connection
	Dim rstPubInfo As ADODB.Recordset
	Dim strCnn As String
	Dim strPubID As String
	Dim strPRInfo As String
	Dim lngOffset As Long
	Dim lngLogoSize As Long
	Dim varLogo As Variant
	Dim varChunk As Variant
	
	Const conChunkSize = 100

	' Open a connection.
	Set cnn1 = New ADODB.Connection
	strCnn = "driver={SQL Server};server=srv;" & _
		"uid=sa;pwd=;database=pubs"
	cnn1.Open strCnn
	
	' Open the pub_info table.
	Set rstPubInfo = New ADODB.Recordset
	rstPubInfo.CursorType = adOpenKeyset
	rstPubInfo.LockType = adLockOptimistic
	rstPubInfo.Open "pub_info", cnn1, , , adCmdTable
	
	' Prompt for a logo to copy.
	strMsg = "Available logos are : " & vbCr & vbCr
	Do While Not rstPubInfo.EOF
		strMsg = strMsg & rstPubInfo!pub_id & vbCr & _
			Left(rstPubInfo!pr_info, InStr(rstPubInfo!pr_info, ",") - 1) & _
			vbCr & vbCr
		rstPubInfo.MoveNext
	Loop
	strMsg = strMsg & "Enter the ID of a logo to copy:"
	strPubID = InputBox(strMsg)
	
	' Copy the logo to a variable in chunks.
	rstPubInfo.Filter = "pub_id = '" & strPubID & "'"
	lngLogoSize = rstPubInfo!logo.ActualSize
	Do While lngOffset < lngLogoSize
		varChunk = rstPubInfo!logo.GetChunk(conChunkSize)
		varLogo = varLogo & varChunk
		lngOffset = lngOffset + conChunkSize
	Loop
	
	' Get data from the user.
	strPubID = Trim(InputBox("Enter a new pub ID:"))
	strPRInfo = Trim(InputBox("Enter descriptive text:"))
	
	' Add a new record, copying the logo in chunks.
	rstPubInfo.AddNew
	rstPubInfo!pub_id = strPubID
	rstPubInfo!pr_info = strPRInfo

	lngOffset = 0   ' Reset offset.
	Do While lngOffset < lngLogoSize
		varChunk = LeftB(RightB(varLogo, lngLogoSize - lngOffset), _
			conChunkSize)
		rstPubInfo!logo.AppendChunk varChunk
		lngOffset = lngOffset + conChunkSize
	Loop
	rstPubInfo.Update
	
	 ' Show the newly added data.
	MsgBox "New record: " & rstPubInfo!pub_id & vbCr & _
		"Description: " & rstPubInfo!pr_info & vbCr & _
		"Logo size: " & rstPubInfo!logo.ActualSize

	' Delete new record because this is a demonstration.
	rstPubInfo.Requery
	cnn1.Execute "DELETE FROM pub_info " & _
		"WHERE pub_id = '" & strPubID & "'"

	rstPubInfo.Close
	cnn1.Close	

End Sub