oracle中可以用多种方法来检索或操作lob数据

（二）在vb中的处理
    在vb中处理大对象，一般可以用OO4O(oracle objects for
    ole)来处理大对象。这里介绍一种不用0040处理大对象blob的方法。
    下面这段程序可以将一个文件（文本文件，doc文件，图象文件等）保存到数据库中，并可以将其从数据库读出
    需要两个commandbutton
    cmd1 名称 cmdsave caption 保存
    cmd2 名称 cmdread caption 读取
    一个cmddialog控件
    同时需要创建一张表t_demo(字段id 类型 number,;字段text 类型 blob;)
    exmple 3.

Option Explicit  Dim rn As ADODB.Connection  Public Function CreateDataSource(DataSource As String, UserID  As String, Password As String) As Boolean  On Error GoTo DbConErr:  Set rn = New ADODB.Connection  With rn  .ConnectionString = "Provider=OraOledb.Oracle.1;" & _  "password=" & Password & ";" & _  "User ID =" & UserID & ";" & _  "Data Source=" & DataSource & ";" & _  "Locale Identifier=2052"  .Open  End With  CreateDataSource = True  Exit Function  DbConErr:  CreateDataSource = False  End Function    Private Sub cmdRead_Click()  Dim rs As New ADODB.Recordset  rs.ActiveConnection = rn  rs.LockType = adLockOptimistic  rs.CursorLocation = adUseClient  rs.Source = "select * from t_demo"  rs.Open  ComDlgDir.DialogTitle = "保存文件"  ComDlgDir.Filter = "*.*"  ComDlgDir.ShowSave  Call BlobToFile(rs.Fields("text"), ComDlgDir.filename)  Set rs = Nothing  Exit Sub  Set rs = Nothing  End Sub    Private Sub cmdsave_Click()  Dim rs As New ADODB.Recordset  rs.ActiveConnection = rn  rs.LockType = adLockOptimistic  rs.CursorLocation = adUseClient  rs.Source = "select * from t_demo"  rs.Open  rs.AddNew  ComDlgDir.DialogTitle = "选取文件"  ComDlgDir.ShowOpen  rs.Fields("id").Value = 1  If ComDlgDir.filename <> "" Then  Call FileToBlob(rs.Fields("text"), ComDlgDir.filename)  rs.Update  End If  Set rs = Nothing  Exit Sub  Set rs = Nothing  End Sub    Private Sub Form_Load()  If Not CreateDataSource("sid", "systemp", "manager") Then  MsgBox "Connection failure!"  End If  End Sub    fld As ADODB.Field, filename As String, Optional ChunkSize As  Long = 8192)  Dim fnum As Integer, bytesleft As Long, bytes As Long  Dim tmp() As Byte  If (fld.Attributes And adFldLong) = 0 Then  Err.Raise 1001, , "field doesn't support the GetChunk method."    End If  If Dir$(filename) = "" Then Err.Raise 53, , "File not found"  fnum = FreeFile  Open filename For Binary As fnum  bytesleft = LOF(fnum)  Do While bytesleft  bytes = bytesleft  If bytes > ChunkSize Then bytes = ChunkSize  ReDim tmp(1 To bytes) As Byte  Get fnum, , tmp  fld.AppendChunk tmp  bytesleft = bytesleft - bytes  Loop  Close #fnum  End Sub    Sub BlobToFile(fld As ADODB.Field, filename A

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