ms-access - MS Access (Jet) 事务、工作区

Question

我在提交事务时遇到问题(使用 Access 2003 DAO)。就好像我从未调用过 BeginTrans 一样——我在 CommitTrans 上收到错误 3034，“您尝试提交或回滚事务而不首先开始事务”；并将更改写入数据库(可能是因为它们从未包装在事务中)。但是，如果您单步执行 BeginTrans，则会运行它。

我使用 DBEngine(0) 工作区在 Access 环境中运行它。

我要添加记录的表都是通过 Jet 数据库连接(到同一个数据库)并使用 DAO.Recordset.AddNew/Update 打开的。

在启动 BeforeTrans 之前打开连接。

我在事务的中间没有做任何奇怪的事情，比如关闭/打开连接或多个工作区等。

有两个嵌套事务级别。基本上它将多个插入包装在一个外部事务中，所以如果有任何失败，它们都会失败。内部事务运行没有错误，外部事务不起作用。

以下是我调查并排除的一些事情:

事务分布在多个方法中，BeginTrans 和 CommitTrans(和 Rollback)都在不同的位置。但是当我尝试以这种方式运行事务的简单测试时，这似乎并不重要。

我想当数据库连接超出本地范围时可能会关闭，即使我有另一个“全局”引用(老实说，我不确定 DAO 对 dbase 连接做了什么)。但情况似乎并非如此——就在提交之前，连接及其记录集是事件的(我可以检查它们的属性，EOF = False 等)

我的 CommitTrans 和 Rollback 在事件回调中完成。 (基本上:解析器程序在解析结束时抛出一个“onLoad”事件，我通过提交或回滚我在处理过程中所做的插入来处理它，这取决于是否发生了任何错误。)但是，再次尝试一个简单的测试，这似乎并不重要。

任何想法为什么这对我不起作用？

谢谢。

编辑 5 月 25 日

这是(简化的)代码。与交易有关的关键点是:

工作区是 DBEngine(0)，在公共(public)(全局)变量 APPSESSION 中引用.

数据库连接在下面的 LoadProcess.cache 中打开，见行 Set db = APPSESSION.connectionTo(dbname_) .

在 LoadProcess.cache 中调用 BeginTrans。

CommitTrans 在 process__onLoad 回调中被调用。

在 process__onInvalid 回调中调用回滚。

记录集更新在 process__onLoadRow、logLoadInit 和 logLoad

中完成

埃里克

'------------------- 
'Application globals
'-------------------

Public APPSESSION As DAOSession

'------------------
' Class LoadProcess
'------------------

Private WithEvents process_ As EventedParser
Private errs_ As New Collection

Private dbname_ As String
Private rawtable_ As String
Private logtable_ As String
Private isInTrans_ As Integer

Private raw_ As DAO.Recordset
Private log_ As DAO.Recordset
Private logid_ As Variant

Public Sub run
    '--- pre-load
    cache
    resetOnRun    ' resets load state variables per run, omitted here
    logLoadInit
    Set process_ = New EventedParser

    '--- load
    process_.Load
End Sub

' raised once per load() if any row invalid
Public Sub process__onInvalid(filename As String)
    If isInTrans_ Then APPSESSION.Workspace.Rollback
End Sub

' raised once per load() if all rows valid, after load
Public Sub process__onLoad(filename As String)
    If errs_.Count > 0 Then
        logLoadFail filename, errs_
    Else
        logLoadOK filename
    End If

    If isInTrans_ Then APPSESSION.Workspace.CommitTrans
End Sub

' raised once per valid row
' append data to raw_ recordset
Public Sub process__onLoadRow(row As Dictionary)
On Error GoTo Err_

    If raw_ Is Nothing Then GoTo Exit_   
    DAOext.appendFromHash raw_, row, , APPSESSION.Workspace

Exit_:
    Exit Sub

Err_:
    ' runtime error handling done here, code omitted
    Resume Exit_

End Sub


Private Sub cache()
Dim db As DAO.Database

    ' TODO raise error
    If Len(dbname_) = 0 Then GoTo Exit_       
    Set db = APPSESSION.connectionTo(dbname_)
    ' TODO raise error
    If db Is Nothing Then GoTo Exit_ 

    Set raw_ = db.OpenRecordset(rawtable_), dbOpenDynaset)
    Set log_ = db.OpenRecordset(logtable_), dbOpenDynaset)    

    APPSESSION.Workspace.BeginTrans
    isInTrans_ = True

Exit_:
    Set db = Nothing

End Sub

' Append initial record to log table
Private Sub logLoadInit()
Dim info As New Dictionary
On Error GoTo Err_

    ' TODO raise error?
    If log_ Is Nothing Then GoTo Exit_   

    With info
        .add "loadTime", Now
        .add "loadBy", CurrentUser
    End With

    logid_ = DAOext.appendFromHash(log_, info, , APPSESSION.Workspace)

Exit_:
    Exit Sub

Err_:
    ' runtime error handling done here, code omitted
    Resume Exit_

End Sub

Private Sub logLoadOK(filename As String)
    logLoad logid_, True, filename, New Collection
End Sub

Private Sub logLoadFail(filename As String, _
                      errs As Collection)
    logLoad logid_, False, filename, errs
End Sub

' Update log table record added in logLoadInit
Private Sub logLoad(logID As Variant, _
                    isloaded As Boolean, _
                    filename As String, _
                    errs As Collection)

Dim info As New Dictionary
Dim er As Variant, strErrs As String
Dim ks As Variant, k As Variant
On Error GoTo Err_

    ' TODO raise error?
    If log_ Is Nothing Then GoTo Exit_   
    If IsNull(logID) Then GoTo Exit_

    For Each er In errs
        strErrs = strErrs & IIf(Len(strErrs) = 0, "", vbCrLf) & CStr(er)
    Next Er

    With info
        .add "loadTime", Now
        .add "loadBy", CurrentUser
        .add "loadRecs", nrecs
        .add "loadSuccess", isloaded
        .add "loadErrs", strErrs
        .add "origPath", filename
    End With

    log_.Requery
    log_.FindFirst "[logID]=" & Nz(logID)
    If log_.NoMatch Then
        'TODO raise error
    Else
        log_.Edit
        ks = info.Keys
        For Each k In ks
            log_.Fields(k).Value = info(k)
        Next k
        log_.Update
    End If

Exit_:
    Exit Sub

Err_:
    ' runtime error handling done here, code omitted
    Resume Exit_

End Sub


'-------------
' Class DAOExt
'-------------
' append to recordset from Dictionary, return autonumber id of new record
Public Function appendFromHash(rst As DAO.Recordset, _
                          rec As Dictionary, _
                          Optional map As Dictionary, _
                          Optional wrk As DAO.workspace) As Long
Dim flds() As Variant, vals() As Variant, ifld As Long, k As Variant
Dim f As DAO.Field, rst_id As DAO.Recordset
Dim isInTrans As Boolean, isPersistWrk As Boolean
On Error GoTo Err_

    ' set up map (code omitted here)

    For Each k In rec.Keys
        If Not map.Exists(CStr(k)) Then _
            Err.Raise 3265, "appendFromHash", "No field mapping found for [" & CStr(k) & "]"
        flds(ifld) = map(CStr(k))
        vals(ifld) = rec(CStr(k))
        ifld = ifld + 1
    Next k

    If wrk Is Nothing Then
        isPersistWrk = False
        Set wrk = DBEngine(0)
    End If

    wrk.BeginTrans
        isInTrans = True
        rst.AddNew
        With rst
            For ifld = 0 To UBound(flds)
                .Fields(flds(ifld)).Value = vals(ifld)
            Next ifld
        End With
        rst.Update

        Set rst_id = wrk(0).OpenRecordset("SELECT @@Identity", DAO.dbOpenForwardOnly, DAO.dbReadOnly)
        appendFromHash = rst_id.Fields(0).Value

    wrk.CommitTrans
    isInTrans = False

Exit_:
    On Error GoTo 0
    If isInTrans And Not wrk Is Nothing Then wrk.Rollback
    If Not isPersistWrk Then Set wrk = Nothing
    Exit Function

Err_:
    ' runtime error handling, code omitted here
    Resume Exit_

End Function


'-----------------
' Class DAOSession (the part that deals with the workspace and dbase connections)
'-----------------
Private wrk_ As DAO.workspace
Private connects_ As New Dictionary
Private dbs_ As New Dictionary

Public Property Get workspace() As DAO.workspace
    If wrk_ Is Nothing Then
        If DBEngine.Workspaces.Count > 0 Then
            Set wrk_ = DBEngine(0)
        End If
    End If
    Set workspace = wrk_
End Property

Public Property Get connectionTo(dbname As String) As DAO.database
    connectTo dbname
    Set connectionTo = connects_(dbname)
End Property

Public Sub connectTo(dbname As String)
Dim Cancel As Integer
Dim cnn As DAO.database
Dim opts As Dictionary
    Cancel = False

    ' if already connected, use cached reference
    If connects_.Exists(dbname) Then GoTo Exit_

    If wrk_ Is Nothing Then _
        Set wrk_ = DBEngine(0)

    ' note opts is a dictionary of connection options, code omitted here
    Set cnn = wrk_.OpenDatabase(dbs_(dbname), _
                                CInt(opts("DAO.OPTIONS")), _
                                CBool(opts("DAO.READONLY")), _
                                CStr(opts("DAO.CONNECT")))

    ' Cache reference to dbase connection
    connects_.Add dbname, cnn

Exit_:
    Set cnn = Nothing
    Exit Sub

End Sub

Answer 1

通过定义一个工作区(它不必是一个新的)来使用事务，然后在该工作区上开始事务，做你需要用它做的事情，如果一切顺利，然后提交事务。骨架代码:

  On Error GoTo errHandler
    Dim wrk As DAO.Workspace

    Set wrk = DBEngine(0) ' use default workspace
    wrk.BeginTrans
    [do whatever]
    If [conditions are met] Then
       wrk.CommitTrans
    Else
       wrk.Rollback
    End If

  errHandler:
    Set wrk = Nothing

  exitRoutine:
    ' do whatever you're going to do with errors
    wrk.Rollback
    Resume errHandler

现在，在您 [做任何事情] 的 block 中，您可以将工作区、数据库和记录集传递给子例程，但顶层控制结构应该保留在一个地方。

您的代码不会这样做 - 相反，您依赖于全局变量。全局变量是邪恶的。不要使用它们。相反，将私有(private)变量作为参数传递给要对其进行操作的子例程。我还要说，永远不要传递工作区——只传递你用工作区创建的对象。

一旦你吸收了这一点，也许它会帮助你解释你的代码应该完成什么(通过阅读它我没有最模糊的想法)，然后我们可以告诉你你做错了什么.