Question

我在一些excel程序中使用以下内容来建立与数据库的连接。

Private Const strConn As String = _
    "PROVIDER=SQLOLEDB.1 ..."     

Sub OpenConnection()

Set cn = CreateObject("ADODB.Connection")
cn.Open strConn
cn.CommandTimeout = 0
Set rs = CreateObject("ADODB.Recordset")
Set rs.ActiveConnection = cn

End Sub

在后续代码中，我使用各种SQL字符串打开连接我想测试rs是否打开，所以我知道它需要关闭，但以下内容不起作用。如何更改以下条件才能正常工作？

If (rs.Open = True) Then
    rs.Close
End If

以下有效，但我不想以这种方式使用错误捕获：

On Error Resume Next
    rs.Close

Answer 1

ADO Recordset具有.State属性，您可以检查其值是adStateClosed还是adStateOpen

If Not (rs Is Nothing) Then
  If (rs.State And adStateOpen) = adStateOpen Then rs.Close
  Set rs = Nothing
End If

MSDN about State property

编辑; 不检查.State对1或0的原因是因为即使它在99.99％的时间内工作，仍然可能有other flags set这将导致If语句失败adStateOpen检查。

EDIT2：

对于未引用ActiveX数据对象的后期绑定，您几乎没有选项。使用ObjectStateEnum

中的adStateOpen常量值

If Not (rs Is Nothing) Then
  If (rs.State And 1) = 1 Then rs.Close
  Set rs = Nothing
End If

或者你可以自己定义常量以使你的代码更具可读性（将它们全部定义为一个很好的例子。）

Const adStateClosed As Long = 0 'Indicates that the object is closed.
Const adStateOpen As Long = 1 'Indicates that the object is open.
Const adStateConnecting As Long = 2 'Indicates that the object is connecting.
Const adStateExecuting As Long = 4 'Indicates that the object is executing a command.
Const adStateFetching As Long = 8 'Indicates that the rows of the object are being retrieved.    

[...]

If Not (rs Is Nothing) Then

    ' ex. If (0001 And 0001) = 0001 (only open flag) -> true
    ' ex. If (1001 And 0001) = 0001 (open and retrieve) -> true
    '    This second example means it is open, but its value is not 1
    '    and If rs.State = 1 -> false, even though it is open
    If (rs.State And adStateOpen) = adStateOpen Then 
        rs.Close
    End If

    Set rs = Nothing
End If

Answer 2

这是一个古老的话题，但是如果其他人仍在寻找...

停靠事件发生后，我遇到了麻烦。即使重新连接到网络，保存在全局对象中的打开的数据库连接也会出错。这是由于TCP连接被远程主机强行终止。（错误-2147467259：TCP提供程序：远程主机强行关闭了现有连接。）

但是，该错误只会在尝试第一个事务后出现。到目前为止，Connection.State和Connection.Version（根据上述解决方案）都不会显示任何错误。

所以我在下面写了一个小的sub来强制执行错误-希望它有用。

在我的设置（Access 2016，SQL Svr 2008R2）上的性能测试大约是每次调用0.5毫秒。

Function adoIsConnected(adoCn As ADODB.Connection) As Boolean

    '----------------------------------------------------------------
    '#PURPOSE: Checks whether the supplied db connection is alive and
    '          hasn't had it's TCP connection forcibly closed by remote
    '          host, for example, as happens during an undock event
    '#RETURNS: True if the supplied db is connected and error-free, 
    '          False otherwise
    '#AUTHOR:  Belladonna
    '----------------------------------------------------------------

    Dim i As Long
    Dim cmd As New ADODB.Command

    'Set up SQL command to return 1
    cmd.CommandText = "SELECT 1"
    cmd.ActiveConnection = adoCn

    'Run a simple query, to test the connection
    On Error Resume Next
    i = cmd.Execute.Fields(0)
    On Error GoTo 0

    'Tidy up
    Set cmd = Nothing

    'If i is 1, connection is open
    If i = 1 Then
        adoIsConnected = True
    Else
        adoIsConnected = False
    End If

End Function

Answer 3

这个主题很老但是如果像我这样的其他人搜索解决方案，这是我找到的解决方案：

type AB = Kleisli[Try, A, B]
type BC = Kleilsi[Try, B, C]
type CD = Kleisli[Try, C, D]

type XReader[T] = Reader[X, T]

val fooXAB: XReader[AB] = ...
val fooXBC: XReader[BC] = ...
val fooXCD: XReader[CD] = ...

val fooXAC: XReader[AC] =
  for {
    ab <- fooXAB
    bc <- fooXBC
    cd <- fooXCD
  } yield (ab andThen bc andThen cd)

所以＆＃34; myBase＆＃34;是一个数据库对象，我已经创建了一个访问数据库的类（带有插入，更新等的类......），并且该模块上的类是在对象中使用声明（显然），我可以使用＆＃34测试连接; [对象] .DBStats＆＃34;：

Public Function DBStats() As Boolean
    On Error GoTo errorHandler
        If Not IsNull(myBase.Version) Then 
            DBStats = True
        End If
        Exit Function
    errorHandler:
        DBStats = False  
End Function

编辑：在DBOpen中我使用＆＃34; OpenDatabase＆＃34;在DBClose中我使用＆＃34; .Close＆＃34;并且＆＃34;设置myBase = nothing＆＃34; 编辑2：在函数中，如果你没有连接，.version会给你一个错误，所以如果没有连接，errorHandler会给你错误的

检查ADODB连接是否已打开

3 个答案: