SUMMARY

OLE DB specification doesn't provide interfaces to compact or repair databases. However, the OLE DB Provider for Microsoft Jet version 4.0 exposes this functionality through a custom interface: IJetCompact (TDataSource cotype). IJetCompact is defined in the header file Jetoledb.h that can be obtained separately from Microsoft (Please see knowledge base article Q228525).

MORE INFORMATION

To repair and compact a Microsoft Access database using OLE DB, MDAC 2.1 or higher version must be properly installed on the computer. The following steps are required:

1.         Create and initialize the data source objects by using interfaces of IDBInitialize and IDBCreateSession.

2.         Use GetJetEngineType function to get the version of Jet database.

3.         Fill a DBPROPSET structure with information about the destination database to compact to.

4.         Query the IDBCreateSession object for the Jet Compact object: IJetCompact.

5.         Call IJetCompact's Compact method passing in the DBPROPSET created in step 2.

The following code demonstrates the earlier steps using Visual C++ ATL OLE DB consumer templates:

#include <objbase.h>

#define DBINITCONSTANTS

#define INITGUID

#include <initguid.h>

#include <oledb.h>

#include "msjetoledb.h"

#include "jetoledb.h" // for IJetCompact interface

#include <atldbcli.h>

long GetJetEngineType( LPCTSTR src );

class OLEINITIALIZE

{

    bool m_bOleInit;

public:

    OLEINITIALIZE()

    {

          m_bOleInit= (CoInitialize(NULL)==S_OK);          

    }

    ~OLEINITIALIZE()

    {

          if (m_bOleInit)

          CoUninitialize();

    }

};

HRESULT CompactDatabase(LPCTSTR src, LPCTSTR dest)

{

    // Initialize environment must be the first line in your function

    OLEINITIALIZE oleinit;

    CDataSource ds;

    CComPtr<IJetCompact> spJetCompact =NULL;

    CComPtr<IDBCreateSession> spSession =NULL;

    HRESULT     hr=0;

    //Specify the source DSO

    ds.Open(CLSID_JETOLEDB_4_00, src);

    CDBPropSet propset1(DBPROPSET_DBINIT);

        propset1.AddProperty(DBPROP_INIT_DATASOURCE, dest);

    long x = GetJetEngineType( src );

    CDBPropSet propset2(DBPROPSET_JETOLEDB_DBINIT);

    propset2.AddProperty(DBPROP_JETOLEDB_ENGINE, x);

    CDBPropSet dbsets[2] = { propset1, propset2 };

    // Have we connected to the database?

    ATLASSERT(ds.m_spInit != NULL);

          hr = ds.m_spInit->QueryInterface(IID_IDBCreateSession, (void**)&spSession);

    if (FAILED(hr))

          return hr;

    //IJetCompact only supported in Jet 4.0 and above

    hr = spSession->QueryInterface( __uuidof(IJetCompact), (void**)&spJetCompact);

    if (FAILED(hr))

          return hr;

    //Delete the destination file if it exists

    remove(dest);

    //Ok compact

    //hr = spJetCompact->Compact(1, &propset);

    hr = spJetCompact->Compact(1, dbsets);

    if (FAILED(hr))

          return hr;

    return hr;

}

long GetJetEngineType( LPCTSTR src )

{

    HRESULT hr;

    CDataSource ds;

    CComBSTR bstrSource;

    VARIANT vPropValue;

    // Initialize our variant to VT_I4 and 0.

    vPropValue.vt   = VT_I4;

    vPropValue.lVal = 0L;

    // Exit now if source database is null.

    if( NULL == src ) return 0;

    // Build connection string for source.

    bstrSource = L"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=";

    bstrSource += src;

    bstrSource += L";";

    hr = ds.OpenFromInitializationString( bstrSource );

    hr = ds.GetProperty( DBPROPSET_JETOLEDB_DBINIT, DBPROP_JETOLEDB_ENGINE, &vPropValue );<BR/>

<BR/>

// Version returned will be one of these values:

    // 

    // #define JETDBENGINETYPE_UNKNOWN   0x00

    // #define JETDBENGINETYPE_JET10     0x01

    // #define JETDBENGINETYPE_JET11     0x02

    // #define JETDBENGINETYPE_JET2X     0x03

    // #define JETDBENGINETYPE_JET3X     0x04

    // #define JETDBENGINETYPE_JET4X     0x05

    return vPropValue.lVal;

}

NOTE:

1.         If you have a compiler error such as:

DBPROP_JETOLEDB_ENGINE undefined specifier

For additional information about updated Jet header files, please click the article number below to view the article in the Microsoft Knowledge Base:

228525 PATCH: JetVC.exe VC++ Support Files for the Jet OLE DB Provider

2.         Inline the GetJetEngineType function in your code if you don't want to open another connection.

3.         Compacting a database also repairs the database, unlike in DAO where it was a separate functionality. In OLE DB there is no way to only repair a database.

REFERENCES

For additional information, please click the article number below to view the article in the Microsoft Knowledge Base:

230501 HOWTO: Compacting Microsoft Access Database via ADO

The information in this article applies to:

           Microsoft OLE DB Provider for Jet 4.0

           Microsoft Data Access Components 2.1

           Microsoft Data Access Components 2.5

           Microsoft Data Access Components 2.6