HOWTO: A C++ Sample of ADO Recordset XML Persistence

Summary

With ADO 2.5 and later, Recordset objects can be persisted into any object that implements the IStream interface. The sample code in this article shows how to persist/load ADO Recordset to/from an external xml file, ADO IStream Object and XML DOM object.

More Information

1. The sample uses authors table in the pubs database of SQL Server Database.

2. Modify the connection string to supply the right datasource name and user credentials.

3. Since there are two #import dll, for simplicity of programing, I rename the ADO(ADODB)namespace as MSXML, and use MSXML for the interfaces defined in both dlls. Alternatively, you can always prefix the interface with appropriate namespace without doing this.

Note You must change User ID=<username> and Password =<strong password> to the correct values before you run this code. Make sure that User ID has the appropriate permissions to perform this operation on the database.
// 1. ADO Recordset <-> external xml file
// 2. ADO Recordset <-> ADO IStream Object
// 3. ADO Recordset <-> DOM Document

#import "C:\Program files\Common Files\System\Ado\msado15.dll" rename_namespace("MSXML") rename("EOF", "ADOEOF")

#import "c:\winnt\system32\msxml.dll"
using namespace MSXML;

#include "stdio.h"
#include "io.h"
void dump_error(_com_error &e) ; //exception handling

void main()
{
HRESULT hr;
CoInitialize(NULL);

try
{
//open the connection, get the reocrdset ready
_ConnectionPtr pConn;
_RecordsetPtr pRs;

hr = pConn.CreateInstance(__uuidof(Connection));
hr = pRs.CreateInstance(__uuidof(Recordset));

pConn->CursorLocation = adUseClient;
_bstr_t strConn("Provider=sqloledb;Data Source=juliaj01;Initial Catalog=pubs;User Id=<username>;Password=<strong password>;");
hr = pConn->Open(strConn, "<username>", "<strong password>", adConnectUnspecified);
hr = pRs->Open("SELECT * from authors", pConn.GetInterfacePtr(), adOpenForwardOnly, adLockReadOnly, adCmdText);

//preparation to save RS as xml file,
struct _finddata_t xml_file;
long hFile;
if( (hFile = _findfirst("authors.xml", &xml_file )) != -1L)
{
DeleteFile("authors.xml"); //if the file exists, delete it
}

// 1. Persist it to an external xml file by calling Save with file name and adPersistXML
hr = pRs->Save("authors.xml", adPersistXML);

// 2. Persist it to ADO IStream Object
_StreamPtrpStream ; //declare one first
pStream.CreateInstance(__uuidof(Stream)); //create it after
hr = pRs->Save(pStream.GetInterfacePtr(), adPersistXML); //old trick, call Save

// 3. Persist it to DOM Document
IXMLDOMDocumentPtr pXMLDOMDoc;
pXMLDOMDoc.CreateInstance(__uuidof(DOMDocument));
hr = pRs->Save(pXMLDOMDoc.GetInterfacePtr(), adPersistXML);
// if you want to check out the content call printf(pXMLDOMDoc->Getxml());

//Recycle the Recordset object
hr = pRs->Close();

// 4. load the recordset back from the file by calling Open with MSPersist provider and adCmdFile.
// the Recordset will be a ReadOnly, Forwardly only
hr = pRs->Open("authors.xml","Provider=MSPersist;",adOpenForwardOnly,adLockReadOnly,adCmdFile);
hr = pRs->Close();

// 5. Load from IStream object, call Open, first param is pStream.GetInterfacePtr()

// Set the steam object position to the beginning of the stream:
pStream->Position = 0;

// call Open, passing in vtMissing for connection string, see Q245485 for details
hr = pRs->Open(pStream.GetInterfacePtr(),vtMissing, adOpenForwardOnly,adLockReadOnly,adCmdFile);

hr = pRs->Close();

// 6 .Load from DOM Document, call Open, first param is pXMLDOMDoc.GetInterfacePtr() and
// pass in vtMissing for connection string, see Q245485

hr = pRs->Open(pXMLDOMDoc.GetInterfacePtr(), vtMissing, adOpenForwardOnly, adLockReadOnly, adCmdFile);

hr = pRs->Close();



//Don't forget to clean up the stream object
hr = pStream->Close();

}
catch(_com_error &e)
{
dump_error(e);
}
}

void dump_error(_com_error &e)
{
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());

// Print Com errors.
printf("Error\n");
printf("\tCode = %08lx\n", e.Error());
printf("\tCode meaning = %s", e.ErrorMessage());
printf("\tSource = %s\n", (LPCSTR) bstrSource);
printf("\tDescription = %s\n", (LPCSTR) bstrDescription);

}
Note The sample code provided in this article contains a reference to MSXML 2.5 or earlier. If a newer version of MSXML has been installed in replace mode on your machine, the sample code will automatically use this new version. If a newer version of MSXML has been installed in side-by-side mode on your machine, the code may use the older version.

To run the code with MSXML 6.0, the following lines of code have to be changed:
  • Replace:
    #import "C:\Program files\Common Files\System\Ado\msado15.dll" rename_namespace("MSXML") rename("EOF", "ADOEOF")


    #import "c:\winnt\system32\msxml.dll" by using namespace MSXML;
    With:
    #import "C:\Program files\Common Files\System\Ado\msado15.dll" rename_namespace("MSXML2") rename("EOF", "ADOEOF")


    #import "c:\winnt\system32\msxml6.dll" using namespace MSXML2;
  • Replace:
    pXMLDOMDoc.CreateInstance(__uuidof(DOMDocument));
    With:
    pXMLDOMDoc.CreateInstance(__uuidof(DOMDocument60));
To run the code with MSXML 6.0, the following lines of code have to be changed:
  • Replace:
    #import "C:\Program files\Common Files\System\Ado\msado15.dll" rename_namespace("MSXML") rename("EOF", "ADOEOF")


    #import "c:\winnt\system32\msxml.dll" by using namespace MSXML;
    With:
    #import "C:\Program files\Common Files\System\Ado\msado15.dll" rename_namespace("MSXML2") rename("EOF", "ADOEOF")


    #import "c:\winnt\system32\msxml6.dll" using namespace MSXML2;
  • Replace:
    pXMLDOMDoc.CreateInstance(__uuidof(DOMDocument));
    With:
    pXMLDOMDoc.CreateInstance(__uuidof(DOMDocument60));

References

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

245485 Title Author Content Type Language Locale Version Confidentiality Content Status Workgroup MT Publish Date Action

262447 How To Persist/Load OLE DB Rowset to/from XML with ATL OLE DB Consumer Template Classes

259555 PRB: Error Occurs When You Open an ADO Recordset on an XML Stream

Eigenschaften

Artikelnummer: 262450 – Letzte Überarbeitung: 22.06.2014 – Revision: 1

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