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Visual C++多线程DAO处理

 2008-11-14 19:33:33 来源:WEB开发网   
核心提示:在DAO多线程处理中,有许多局限性,Visual C++多线程DAO处理,所以我设计了这么一个类,通过GUI线程来使用DAO的强制调用,你也可以用一个对话框来显示错误信息,它们都应该在MultiDaorecordset.h中被定义,在类中使用了GUI的消息队列,所有进入到CMultiDAORecordset的调用都被迫

在DAO多线程处理中,有许多局限性,所以我设计了这么一个类,通过GUI线程来使用DAO的强制调用。在类中使用了GUI的消息队列,所有进入到CMultiDAORecordset的调用都被迫使用AfxGetThread()来检查当前的线程。GUI线程指针是放在InitInstance的首端,如果在GUI线程中,引入的调用请求不在运行,那么CMultiDAORecordSet就会发送一个WM_MULTIDAOMESSAGE消息给AfxGetMainWnd()(在Mainfrm.cpp中)。Mainfrm接受到这个消息,线程也就要再运行一次,这个时候,消息已经接受了,基类CDaoRecordset也就得到了调用。所以你的类是从CMultiDAORecordset继承的,而不是CDaoRecordset,如下:

  class CMySet : public CMultiDaoRecordSet
  在相应的CPP文件中也应该改一下:
  IMPLEMENT_DYNAMIC(CMySet, CMultiDaoRecordSet)
  CMySet::CMySet (CDaoDatabase* pdb) : CMultiDaoRecordSet(pdb)
为了处理接受到的WM_MULTIDAOMESSAGE消息,下面的代码还应该加在MainFrm中:
  在MainFrm.h文件中加:
#ifdef MAINFRAME_CPP
UINT WM_MULTIDAOMESSAGE = RegisterWindowMessage("WM_MULTIDAOMESSAGE");
#else
extern UINT WM_MULTIDAOMESSAGE;
#endif
  afx_msg LONG OnMultiDaoMessage( UINT uParam, LONG lParam);
在MainFrm.cpp文件中加:
#define MAINFRAME_CPP
  #include "MutliDaoRecordset.h"
  //added to the message map
  BEGIN_MESSAGE_MAP(CMainFrame, CMDIFrameWnd)
//{{AFX_MSG_MAP(CMainFrame)
ON_REGISTERED_MESSAGE(WM_MULTIDAOMESSAGE, OnMultiDaoMessage)
END_MESSAGE_MAP()
  //this function added
LONG CMainFrame::OnMultiDaoMessage( UINT uParam, LONG lParam)
{
//jtm
//based on switch, perform operation...
CMultiDaoRecordSet *pSet = (CMultiDaoRecordSet *)lParam;
LONG lRet = 0;
  CString cRet = "";
COleVariant cVar;
  try
{
//jtm-------debug--------------------------------------
CString cTraceMessage = cDAOMessageArray[uParam];
cTraceMessage += "n";
TRACE(cTraceMessage);
//jtm-------debug--------------------------------------
switch(uParam)
{
case MultiDaoOpen:
pSet->Open();
break;
case MultiDaoClose:
pSet->Close();
break;
case MultiDaoIsOpen:
lRet = (LONG)pSet->IsOpen();
break;
case MultiDaoIsBOF:
lRet = (LONG)pSet->IsBOF();
break;
case MultiDaoIsEOF:
lRet = (LONG)pSet->IsEOF();
break;
case MultiDaoIsDeleted:
lRet = (LONG)pSet->IsDeleted();
break;
case MultiDaoIsFieldDirty:
lRet = (LONG)pSet->IsFieldDirty(pSet->pParam1);
break;
case MultiDaoIsFieldNull:
lRet = (LONG)pSet->IsFieldNull(pSet->pParam1);
break;
case MultiDaoIsFieldNullable:
lRet = (LONG)pSet->IsFieldNullable(pSet->pParam1);
break;
case MultiDaoGetName:
cRet = pSet->GetName();
lRet = (LONG)&cRet;
break;
case MultiDaoGetType:
lRet = (LONG)pSet->GetType();
break;
case MultiDaoGetEditMode:
lRet = (LONG)pSet->GetEditMode();
break;
case MultiDaoGetLastModifiedBookmark:
cVar = pSet->GetLastModifiedBookmark();
lRet = (LONG)&cVar;
break;
case MultiDaoGetRecordCount:
lRet = (LONG)pSet->GetRecordCount();
break;
case MultiDaoMoveNext:
pSet->MoveNext();
break;
case MultiDaoMovePrev:
pSet->MovePrev();
break;
case MultiDaoMoveFirst:
pSet->MoveFirst();
break;
case MultiDaoMoveLast:
pSet->MoveLast();
break;
case MultiDaoMove:
pSet->Move(*(LONG *)pSet->pParam1);
break;
case MultiDaoFindNext:
lRet = (LONG)pSet->FindNext(*(LPCTSTR *)pSet->pParam1);
break;
case MultiDaoFindPrev:
lRet = (LONG)pSet->FindPrev(*(LPCTSTR*)pSet->pParam1);
break;
case MultiDaoFindFirst:
lRet = (LONG)pSet->FindFirst(*(LPCTSTR *)pSet->pParam1);
break;
case MultiDaoFindLast:
lRet = (LONG)pSet->FindLast(*(LPCTSTR *)pSet->pParam1);
break;
case MultiDaoFind:
lRet = (LONG)pSet->Find(*(LONG *)pSet->pParam1, *(LPCTSTR*)pSet->pParam2);
break;
case MultiDaoGetBookmark:
cVar = pSet->GetBookmark();
lRet = (LONG)&cVar;
break;
case MultiDaoSetBookmark:
pSet->SetBookmark(*(COleVariant*)pSet->pParam1);
break;
case MultiDaoAddNew:
pSet->AddNew();
break;
case MultiDaoEdit:
pSet->Edit();
break;
case MultiDaoUpdate:
pSet->Update();
break;
case MultiDaoDelete:
pSet->Delete();
break;
case MultiDaoCancelUpdate:
pSet->CancelUpdate();
break;
case MultiDaoRequery:
pSet->Requery();
break;
}
}
catch (CDaoException *e)
{
TRACE("Database Multithread Operation Failed%sn",
e->m_pErrorInfo->m_strDescription);
}
return lRet;
}
  下面的代码是加在对应的应用程序对象的头文件中的:
public:
CWinThread *pGUIThread;
  And this to the constructor in the app .cpp file:
CMyApp::CMyApp()
{
pGUIThread = AfxGetThread();
}

如果没有上面的定义的话,你的应用程序就会出问题。整个DAO公共函数并没有全部实现,但不管怎么样,上面的函数是保护CDaoRecordset的使用的。如果你要加个函数的话,加进去就行了,你也可以用一个对话框来显示错误信息,它们都应该在MultiDaorecordset.h中被定义。为了支持DAO多线程的类,下面的代码也应该加进去:

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Tags:Visual 线程 DAO

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