AppendChunk和GetChunk方法应用实例(VB)

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本范例使用 AppendChunk 和 GetChunk 方法来用其他记录中的数据填充图像字段。

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 = "Provider=sqloledb;" & _
        "Data Source=srv;Initial Catalog=Pubs;User Id=sa;Password=; "
    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" & _
                            " [must be > 9899 & < 9999]:"))
    strPRInfo = Trim(InputBox("Enter descriptive text:"))

   ' Add the new publisher to the publishers table to avoid
   ' getting an error due to foreign key constraint.
   cnn1.Execute "INSERT publishers(pub_id, pub_name) VALUES('" & _
                  strPubID & "','Your Test Publisher')"
   
    ' 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 records because this is a demonstration.
    rstPubInfo.Requery
    cnn1.Execute "DELETE FROM pub_info " & _
        "WHERE pub_id = '" & strPubID & "'"

   cnn1.Execute "DELETE FROM publishers " & _
      "WHERE pub_id = '" & strPubID & "'"

    rstPubInfo.Close
    cnn1.Close   

End Sub

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