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

  • Live Event Date: December 11, 2014 @ 1:00 p.m. ET / 10:00 a.m. PT Market pressures to move more quickly and develop innovative applications are forcing organizations to rethink how they develop and release applications. The combination of public clouds and physical back-end infrastructures are a means to get applications out faster. However, these hybrid solutions complicate DevOps adoption, with application delivery pipelines that span across complex hybrid cloud and non-cloud environments. Check out this …

  • Hundreds of millions of users have adopted public cloud storage solutions to satisfy their Private Online File Sharing and Collaboration (OFS) needs. With new headlines on cloud privacy issues appearing almost daily, the need to explore private alternatives has never been stronger. Join ESG Senior Analyst Terri McClure and Connected Data in this on-demand webinar to take a look at the business drivers behind OFS adoption, how organizations can benefit from on-premise deployments, and emerging private OFS …

Most Popular Programming Stories

More for Developers

RSS Feeds