Q254021: HOWTO: Return an Array of Recordsets from an ADO/RDS Server
Article: Q254021
Product(s): Microsoft C Compiler
Version(s): 2.1,2.5,2.6,6.0SP3
Operating System(s):
Keyword(s): kbGrpDSVCDB kbGrpDSMDAC kbDSupport kbMDAC260 kbATM kbmdac270
Last Modified: 23-AUG-2001
This article assumes intermediate knowledge of ATL, ADO and RDS technologies.
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The information in this article applies to:
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0sp3
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0sp3
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0sp3
- Microsoft Data Access Components versions 2.1, 2.5, 2.6, 2.7
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SUMMARY
=======
This article demonstrates one way to pass an array of Recordsets from an ActiveX
Data Objects (ADO)/Remote Data Service (RDS) server.
MORE INFORMATION
================
The following Active Template Library (ATL) server has been tested against the
Pubs database in SQL Server version 7.0. You must have a valid data source name
(DSN) that is named "MyDSN" and that points to the Pubs database in order to
conduct the test successfully.
Steps to Create the ATL Server
------------------------------
1. Use Appwizard to create an ATL server. You can accept the default server type
Dynamic Link Library to create an in-proc server.
2. Add support for MFC and allow merging of proxy/stub code.
3. Right click the server, browse to Add ATL object, and then add a full
Control. Name your control MyRsArray.
4. Right click the interface for your control class (IMyRsArray), and browse to
Add Method. Add a method and name it GetRsArray. This method should take a
VARIANT * as an [in,out] parameter.
5. Paste the code below into the GetRsArray method implementation:
STDMETHODIMP CMyRsArray::GetRsArray(VARIANT * pvar)
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())
HRESULT hr;
_variant_t var1, var2; // Variants to wrap the recordsets.
// Clear return value.
VariantClear(pvar);
SAFEARRAY * pSA;
// Create the safearray.
SAFEARRAYBOUND sabRSarray[1]; // A one-dimensional array.
sabRSarray[0].cElements=2; // Two elements.
sabRSarray[0].lLbound=0; //Lower bound of array.
pSA=SafeArrayCreate(VT_VARIANT,1, sabRSarray);
try
{
// Create the recordsets.
_RecordsetPtr RS1(__uuidof(Recordset));
_RecordsetPtr RS2(__uuidof(Recordset));
_ConnectionPtr spConn1(__uuidof(Connection));
_ConnectionPtr spConn2(__uuidof(Connection));
// Make sure you pass valid connection properties to connect and get recordsets.
hr=spConn1->Open(OLESTR("dsn=MyDSN"),OLESTR("user_id"),
OLESTR("password"), -1);
hr=spConn2->Open(OLESTR("dsn=MyDSN"),OLESTR("user_id"),
OLESTR("password"), -1);
// Disconnected recordsets must use adUseClient.
RS1->CursorLocation = adUseClient;
RS2->CursorLocation = adUseClient;
hr=RS1->Open(OLESTR("select * from authors"), spConn1.GetInterfacePtr(), adOpenKeyset, adLockBatchOptimistic, adCmdText);
hr=RS2->Open(OLESTR("select * from authors"), spConn2.GetInterfacePtr(), adOpenStatic, adLockBatchOptimistic, -1);
// Disassociate the connection from the recordset.
RS1->PutRefActiveConnection(NULL);
RS2->PutRefActiveConnection(NULL);
// Copy IDispatch pointer of recordset into our _variant_t array.
// This will AddRef the recordset one time (refcount now is 2).
var1 = _variant_t( (IDispatch*) RS1 );
var2 = _variant_t( (IDispatch*) RS2 );
RS1 = NULL;
RS2 = NULL; // refcount now is 1, variants contain last reference to recordsets.
// Fill the safearray.
long ndex;
ndex = 0;
hr=SafeArrayPutElement(pSA, &ndex, &var1);
ndex = 1;
hr=SafeArrayPutElement(pSA, &ndex, &var2);
// Load the safearray into an output variable.
pvar->vt = VT_ARRAY|VT_VARIANT;
pvar->parray = pSA;
}
catch( _com_error e)
{
hr = e.Error();
}
return S_OK;
}
NOTES
- pVar is the name of the VARIANT * that is passed as an input to the
GetRsArray method. The same pVar will hold the recordset array as an output
of the GetRsArray method.
- Each recordset is placed into a variant before being placed in the safearray.
- The safearray is then placed into a variant.
- The vt of the variant that the safearray is placed into is set to
VT_ARRAY||VT_VARIANT. This is necessary for marshalling.
REFERENCES
==========
Please refer to the Platform SDK and MSDN for more information on ATL, ADO, and
RDS technologies.
Additional query words: safe array record sets
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Keywords : kbGrpDSVCDB kbGrpDSMDAC kbDSupport kbMDAC260 kbATM kbmdac270
Technology : kbVCsearch kbAudDeveloper kbMDACSearch kbMDAC210 kbMDAC250 kbMDAC260 kbVC32bitSearch kbVC600SP3 kbMDAC270
Version : :2.1,2.5,2.6,6.0SP3
Issue type : kbhowto
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