Using DAO from a DLL

Microsoft's Visual C++ on-line help says that DAO is safe to use in DLL's. Therefore, I created a DLL which I use to access the same database my main application thread is accessing, in order to do a background report with one worker thread..

From the main application's point of view it is creating wrapper objects in a DLL. The wrapper objects, in turn, access the database and return the results to the application.

It is a single-threaded DLL but it could probably be modified to be thread-safe by using locks.

I list the code for one wrapper class here but you could put many different recordset wrappers into the DLL project.

Here's some of the code in my DLL:

class CMyRecordsetWrapper : public CCmdTarget
{
 DECLARE_DYNCREATE(CMyRecordsetWrapper)

 // protected constructor used by dynamic creation
 CMyRecordsetWrapper();           
 CMyRecordsetWrapper(CString filename);

// Attributes
public:
 CMyRecordset* myrecordset;
 long	m_index;
 long	m_time;
 long	m_eventtype; 
 CString	m_title;
 long	m_binarydataindex;
 long	m_offset;
 long	m_length;

// Operations
public:
 void Open(int thetype, LPCTSTR sqlstring, int themode);
 BOOL IsBOF();
 BOOL IsEOF();
 void MoveFirst();
 void MoveLast();
 LONG GetRecordCount();
 void Close();
 void MoveNext();
 BOOL FindNext(LPCTSTR lpszFilter);
 BOOL FindPrev(LPCTSTR lpszFilter);
 BOOL CanRestart();
 void copyem();
 void opentherecordset();

// Overrides
 // ClassWizard generated virtual function overrides
 //{{AFX_VIRTUAL(CMyRecordsetWrapper)
 //}}AFX_VIRTUAL

// Implementation
 virtual ~CMyRecordsetWrapper();

protected:
 // Generated message map functions
 //{{AFX_MSG(CMyRecordsetWrapper)
  // NOTE - the ClassWizard will add and remove member functions here.
 //}}AFX_MSG

 DECLARE_MESSAGE_MAP()
};

CMyRecordsetWrapper::CMyRecordsetWrapper(CString filename)
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  if (theApp.databaseopen == 0)
  {
    AfxDaoInit( );
    theApp.eventdatabase = new CDaoDatabase;
    theApp.eventdatabase->Open(filename);
  }
  // increment reference count
  theApp.databaseopen++;
  opentherecordset();
}

CMyRecordsetWrapper::~CMyRecordsetWrapper()
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  delete myrecordset;
  theApp.databaseopen--;
  if (theApp.databaseopen == 0)
  {
    theApp.eventdatabase->Close();
    delete theApp.eventdatabase;
    AfxDaoTerm();
  }
}

void CMyRecordsetWrapper::opentherecordset()
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  myrecordset = new CMyRecordset(theApp.eventdatabase);
}

void CMyRecordsetWrapper::Close()
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  myrecordset->Close();
}

void CMyRecordsetWrapper::MoveFirst()
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  myrecordset->MoveFirst();
  copyem();
}

void CMyRecordsetWrapper::copyem()
{
  AFX_MANAGE_STATE(AfxGetStaticModuleState());
  m_index = myrecordset->m_index;
  m_time = myrecordset->m_time;
  m_eventtype = myrecordset->m_eventtype;
  m_title = myrecordset->m_title;
  m_binarydataindex = myrecordset->m_binarydataindex;
  m_offset = myrecordset->m_offset;
  m_length = myrecordset->m_length;
}


Comments

  • How to attach table from a database

    Posted by Legacy on 08/01/2002 12:00am

    Originally posted by: LKp

    I want to copy a table from another database to a new database using dao but i don't know how to do it pls help!!!

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Today's agile organizations pose operations teams with a tremendous challenge: to deploy new releases to production immediately after development and testing is completed. To ensure that applications are deployed successfully, an automatic and transparent process is required. We refer to this process as Zero Touch Deployment™. This white paper reviews two approaches to Zero Touch Deployment--a script-based solution and a release automation platform. The article discusses how each can solve the key …

  • Learn How A Global Entertainment Company Saw a 448% ROI Every business today uses software to manage systems, deliver products, and empower employees to do their jobs. But software inevitably breaks, and when it does, businesses lose money -- in the form of dissatisfied customers, missed SLAs or lost productivity. PagerDuty, an operations performance platform, solves this problem by helping operations engineers and developers more effectively manage and resolve incidents across a company's global operations. …

Most Popular Programming Stories

More for Developers

RSS Feeds