Creating a Disconnected Recordset in C++ For VB

Environment: Visual C++ 6.0 and VB 6.0, ADO 1.5

This article assumes that you are familiar with ADO, Visual C++ and ATL.

This article shows how to create a Visual C++ COM object that creates a disconnected ADO Recordset. With a disconnected ADO recordset, your ATL COM object can connect to the database, create the Recordset, and disconnect without having to keep a connection open, while allowing the client to read the data in the Recordset. This works great with MTS where database connection pooling requires this functionality.

Resources: HOWTO: Getting ADO Disconnected Recordsets in VBA/C++/Java
SAMPLE: ATL2ADO.exe Returns Disconnected ADO Recordset

In your project make sure you import dll to create your ADO classes.


#import "c:\program files\common files\system\ado\msado15.dll" no_namespace rename("EOF", "adoEOF") implementation_only

Next create a method with an [out, retval] property of type _Recordset **

[id(1), helpstring("method GetADORecordset")] HRESULT GetADORecordset( [out, retval] _Recordset **ppRecordset);

Your source code should look something like this:

STDMETHODIMP CReturnADO::GetADORecordset(_Recordset **ppRecordset)
{
	
	_ConnectionPtr	pConnection;
	_RecordsetPtr	pRecordset;
	
	try
	{
		pConnection.CreateInstance(__uuidof(Connection));
		pConnection->CursorLocation = adUseClient; // Important for disconnected sets
		pConnection->Open("DSN=SQLSource","loginnmae","password",-1);


		pRecordset.CreateInstance(__uuidof(Recordset));
		pRecordset->CursorLocation = adUseClient; // Important for disconnected sets
		
		pRecordset->PutRefActiveConnection(pConnection.GetInterfacePtr()); // Associate the connection to this recordset

		pRecordset->Open("SELECT DISTINCT name FROM TBLWHATEVER WHERE name IS NOT NULL",vtMissing,
			adOpenForwardOnly, adLockReadOnly,
			adCmdText);

        pRecordset->PutRefActiveConnection(NULL); // Disassociate the connection from the recordset.

		if(pConnection->GetState() == adStateOpen)
			pConnection->Close();
		pConnection = NULL;
		
		*ppRecordset = pRecordset.Detach();

	}
	catch(_com_error *e)
	{
		return AtlReportError(CLSID_ReturnADO,e->ErrorMessage(),IID_IReturnADO,E_FAIL);
	}
	catch(...)
	{
		return AtlReportError(CLSID_ReturnADO,"Unknown Error.",IID_IReturnADO,E_FAIL);
	}

	return S_OK;
}

Now your interface descriptions and CLSID's will be different, but go ahead and use this code to build your own version. Your VB code might look something like this:

    Dim adoset As ADODB.Recordset
    Dim engine As New TESTRETURNADOLib.ReturnADO
    
    Set adoset = engine.GetADORecordset
    While Not adoset.EOF
        List1.AddItem adoset.Fields(0)
        adoset.MoveNext
    Wend
    
    Set adoset = Nothing



Comments

  • There are no comments yet. Be the first to comment!

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

Top White Papers and Webcasts

  • You probably have several goals for your patient portal of choice. Is "community" one of them? With a bevy of vendors offering portal solutions, it can be challenging for a hospital to know where to start. Fortunately, YourCareCommunity helps ease the decision-making process. Read this white paper to learn more. "3 Ways Clinicians can Leverage a Patient Portal to Craft a Healthcare Community" is a published document owned by www.medhost.com

  • Download the Information Governance Survey Benchmark Report to gain insights that can help you further establish business value in your Records and Information Management (RIM) program and across your entire organization. Discover how your peers in the industry are dealing with this evolving information lifecycle management environment and uncover key insights such as: 87% of organizations surveyed have a RIM program in place 8% measure compliance 64% cannot get employees to "let go" of information for …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds