DefinedSize 属性示例 (VB)
此示例演示 Column 的 DefinedSize 属性。 该代码将重新定义 Northwind 数据库的 Employees 表的 FirstName 列的大小。 然后，将显示基于 Employees 表的 Recordset 的 FirstName 字段值的变化。 请注意，默认情况下，在重新定义 DefinedSize 属性后，FirstName 字段将填充空格。
' BeginDefinedSizeVB
Public Sub Main()
On Error GoTo DefinedSizeXError
Dim rstEmployees As ADODB.Recordset
Dim catNorthwind As New ADOX.Catalog
Dim colFirstName As ADOX.Column
Dim colNewFirstName As New ADOX.Column
Dim aryFirstName() As String
Dim i As Integer
Dim strCnn As String
strCnn = "Provider='Microsoft.Jet.OLEDB.4.0';" & _
"Data Source='Northwind.mdb';"
' Open a Recordset for the Employees table.
Set rstEmployees = New ADODB.Recordset
rstEmployees.Open "Employees", strCnn, adOpenKeyset, , adCmdTable
ReDim aryFirstName(rstEmployees.RecordCount)
' Open a Catalog for the Northwind database,
' using same connection as rstEmployees
Set catNorthwind.ActiveConnection = rstEmployees.ActiveConnection
' Loop through the recordset displaying the contents
' of the FirstName field, the field's defined size,
' and its actual size.
' Also store FirstName values in aryFirstName array.
rstEmployees.MoveFirst
Debug.Print " "
Debug.Print "Original Defined Size and Actual Size"
i = 0
Do Until rstEmployees.EOF
Debug.Print "Employee name: " & rstEmployees!FirstName & _
" " & rstEmployees!LastName
Debug.Print " FirstName Defined size: " _
& rstEmployees!FirstName.DefinedSize
Debug.Print " FirstName Actual size: " & _
rstEmployees!FirstName.ActualSize
If Not rstEmployees!FirstName = Null Then
aryFirstName(i) = rstEmployees!FirstName
End If
rstEmployees.MoveNext
i = i + 1
Loop
rstEmployees.Close
' Redefine the DefinedSize of FirstName in the catalog
Set colFirstName = catNorthwind.Tables("Employees").Columns("FirstName")
colNewFirstName.Name = colFirstName.Name
colNewFirstName.Type = colFirstName.Type
colNewFirstName.DefinedSize = colFirstName.DefinedSize + 1
' Append new FirstName column to catalog
catNorthwind.Tables("Employees").Columns.Delete colFirstName.Name
catNorthwind.Tables("Employees").Columns.Append colNewFirstName
' Open Employee table in Recordset for updating
rstEmployees.Open "Employees", catNorthwind.ActiveConnection, _
adOpenKeyset, adLockOptimistic, adCmdTable
' Loop through the recordset displaying the contents
' of the FirstName field, the field's defined size,
' and its actual size.
' Also restore FirstName values from aryFirstName.
rstEmployees.MoveFirst
Debug.Print " "
Debug.Print "New Defined Size and Actual Size"
i = 0
Do Until rstEmployees.EOF
rstEmployees!FirstName = aryFirstName(i)
Debug.Print "Employee name: " & rstEmployees!FirstName & _
" " & rstEmployees!LastName
Debug.Print " FirstName Defined size: " _
& rstEmployees!FirstName.DefinedSize
Debug.Print " FirstName Actual size: " & _
rstEmployees!FirstName.ActualSize
rstEmployees.MoveNext
i = i + 1
Loop
rstEmployees.Close
' Restore original FirstName column to catalog
catNorthwind.Tables("Employees").Columns.Delete colNewFirstName.Name
catNorthwind.Tables("Employees").Columns.Append colFirstName
' Restore original FirstName values to Employees table
rstEmployees.Open "Employees", catNorthwind.ActiveConnection, _
adOpenKeyset, adLockOptimistic, adCmdTable
rstEmployees.MoveFirst
i = 0
Do Until rstEmployees.EOF
rstEmployees!FirstName = aryFirstName(i)
rstEmployees.MoveNext
i = i + 1
Loop
rstEmployees.Close
'Clean up
Set catNorthwind = Nothing
Set colNewFirstName = Nothing
Set colFirstName = Nothing
Set rstEmployees = Nothing
Exit Sub
DefinedSizeXError:
Set catNorthwind = Nothing
Set colNewFirstName = Nothing
Set colFirstName = Nothing
If Not rstEmployees Is Nothing Then
If rstEmployees.State = adStateOpen Then rstEmployees.Close
End If
Set rstEmployees = Nothing
If Err <> 0 Then
MsgBox Err.Source & "-->" & Err.Description, , "Error"
End If
End Sub
' EndDefinedSizeVB