How To Implement Visual C++ COM Objects Returning Recordsets (225131)


The information in this article applies to:

  • Microsoft Active Server Pages
  • ActiveX Data Objects (ADO)
  • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
  • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
  • Microsoft Visual C++, 32-bit Professional Edition 5.0
  • Microsoft Visual C++, 32-bit Professional Edition 6.0
  • Microsoft Visual C++, 32-bit Learning Edition 6.0
  • Microsoft Internet Information Server 4.0
  • Microsoft Internet Information Server 5.0
  • Microsoft Data Access Components 2.5
This article was previously published under Q225131

SUMMARY

This article describes, by example, how to implement a Visual C++ Component Object Model (COM) object that returns a recordset to Active Server Pages (ASP).

Implementing this incorrectly can result in memory leaks or one of the following errors:
The operation requested by the application is not allowed if the object is closed.

-or-

Type Mismatch

-or-

error 'ASP 0115' - A trappable error occured in an external object

MORE INFORMATION

Use the following steps to implement a method that returns a recordset from a Visual C++ COM object to Active Server Pages.
  1. Create an ATL DLL project called PassRs.
  2. Insert an ATL object named PassRsObj.
  3. Add a method with the following information:
    Method Name: TestMethod
Parameters : [out, retval] LPDISPATCH* ppRecordset
  4. Include the following line in the object's implementation file:
    #import "msado15.dll" no_namespace rename("EOF", "adoEOF")
  5. Implement the method as follows:

    Note You must change UID=<username> and pwd=<strong password> to the correct values before you run this code. Make sure that UID has the appropriate permissions to perform this operation on the database.
    STDMETHODIMP CPassRsObj::TestMethod(LPDISPATCH *ppRecordset )
{
    _ConnectionPtr pConn;
    _RecordsetPtr pRs;
	
    pConn.CreateInstance(__uuidof(Connection));
    pRs.CreateInstance(__uuidof(Recordset));

    pConn->Open("DSN=pubs;uid=<username>;pwd=<strong password>;", (BSTR) NULL, (BSTR) NULL, -1);

    //Client side cursor is required for disconnected recordsets
    pRs->CursorLocation = adUseClient;

    pRs->Open( "select * from authors",
               pConn.GetInterfacePtr(),
               adOpenKeyset, adLockOptimistic, -1);

    // Disconnect the recordset
    pRs->PutRefActiveConnection(NULL);

    //Clone the recordset. 
    //NOTE: Recordset to be cloned must support bookmarks
    pRs->Clone(adLockOptimistic)->QueryInterface(IID_IDispatch, (void**) ppRecordset);

    pRs->Close();
    pConn->Close();

    pRs = NULL;
    pConn = NULL;	

    return S_OK;
}
  6. Create an ASP page with the following code:
    <%
Dim rsTest, oTestPassRs

Set oTestPassRs = Server.CreateObject("PassRs.PassRsObj")
Set rsTest = oTestPassRs.TestMethod()

Do 
   Response.Write ( "Value in Record = " & rsTest(1) & "<BR>" )
   rsTest.MoveNext
Loop until rsTest.EOF

rsTest.Close
Set rsTest = Nothing
Set oTestPassRs = Nothing
%>

REFERENCES

For additional information, please see the following articles in the Microsoft Knowledge Base:

184397 How To Getting ADO Disconnected Recordsets in VBA/C++/Java

193515 PRB: Update of Same Record 2x w/Disconnect ADO Recordset Fails

224424 How To Implement Visual Basic COM Objects Returning Recordsets

Modification Type:MinorLast Reviewed:7/1/2004
Keywords:kbCodeSnippet kbDatabase kberrmsg kbhowto KB225131
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