Question

My C++ code successfully restores an SqlServer database backup file and then extracts the necessary information from the resulting database using the OLEDB API.

Here is my C++ code, in the end of which I get an IDBCreateCommand instance ready to be used for executing various queries against the restored database:

DB::DB(LPCWSTR wszDataSource, LPCWSTR wszBackupFilePath, LPCWSTR wszRestoreFolderPath)
{
  fs::path backupFilePath = fs::canonical(wszBackupFilePath).make_preferred();
  fs::path restoreFolderPath = fs::canonical(wszRestoreFolderPath).make_preferred();
  std::wstring db = backupFilePath.leaf().stem().wstring();
  boost::wformat restoreQueryFmt(L"RESTORE DATABASE [%2%] FROM DISK = N'%1%' WITH REPLACE, STATS = 10, MOVE N'%2%' TO N'%3%\\%2%.mdf', MOVE N'%2%_log' TO N'%3%\\%2%.LDF'");
  std::wstring query = (restoreQueryFmt % backupFilePath.wstring() % db % restoreFolderPath.wstring()).str();

  IDBInitializePtr spDBInitialize;
  HRESULT hr = spDBInitialize.CreateInstance(CLSID_SQLNCLI10, NULL);
  if (REGDB_E_CLASSNOTREG == hr)
  {
    hr = spDBInitialize.CreateInstance(CLSID_SQLNCLI, NULL);
  }
  _HRESULT_CHECK3(spDBInitialize, hr);

  _variant_t vDataSource(wszDataSource);
  _variant_t vAuth(L"SSPI");

  DBPROP dbprop[2];          // property used in property set to initialize provider

  dbprop[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
  dbprop[0].dwOptions  = DBPROPOPTIONS_REQUIRED;
  dbprop[0].vValue = vDataSource;

  dbprop[1].dwPropertyID  = DBPROP_AUTH_INTEGRATED;
  dbprop[1].dwOptions = DBPROPOPTIONS_REQUIRED;
  dbprop[1].vValue = vAuth;

  DBPROPSET dbpropset[1];        // Property Set used to initialize provider
  dbpropset[0].guidPropertySet = DBPROPSET_DBINIT;
  dbpropset[0].rgProperties  = dbprop;
  dbpropset[0].cProperties = sizeof(dbprop)/sizeof(dbprop[0]);

   // Set initialization properties.
  IDBPropertiesPtr spDBProperties = spDBInitialize;

  _HRESULT_CHECK(spDBProperties, SetProperties(1, dbpropset));
  _HRESULT_CHECK(spDBInitialize, Initialize());

  IDBCreateSessionPtr spCreateSession = spDBInitialize;
  _HRESULT_CHECK(spCreateSession, CreateSession(NULL, IID_IDBCreateCommand, reinterpret_cast<IUnknown **>(&m_spDBCreateCommand)));

  ICommandTextPtr spCommandText;
  _HRESULT_CHECK(m_spDBCreateCommand, CreateCommand(NULL, IID_ICommandText, reinterpret_cast<IUnknown **>(&spCommandText)));

  _HRESULT_CHECK(spCommandText, SetCommandText(DBGUID_SQL, query.c_str()));
  _HRESULT_CHECK(spCommandText, Execute(NULL, IID_NULL, NULL, NULL, NULL));
  _HRESULT_CHECK(spCommandText, SetCommandText(DBGUID_SQL, (boost::wformat(L"USE \"%1%\"") % db).str().c_str()));
  _HRESULT_CHECK(spCommandText, Execute(NULL, IID_NULL, NULL, NULL, NULL));
}

What it does is:

1. Initializes a new database connection using the given data source (like “.\SQLEXPRESS”) and SSPI integrated authentication scheme.
2. Executes a RESTORE DATABASE T-SQL statement, like this one: RESTORE DATABASE [my_db] FROM DISK = N'c:\temp\my_db.ebf' WITH REPLACE, STATS = 10, MOVE 'my_db' TO N'c:\temp\my_db.mdf', MOVE N'my_db_log' TO N'c:\temp\my_db.LDF'
3. Use the new database for the subsequent queries by running USE "my_db"

So, I have no problems restoring a database backup file and proceding from there.

Now I am facing another problem. Suppose there is no backup file, rather an already existing MDF file – how do I attach to it using the OLEDB C++ API?

Thanks.

EDIT

It is assumed that the .mdf file is accompanied by all the files required by the database engine – .ldf and others as needed.

Answer 1

You cannot attach a database if all you have is and MDF file because that is, at best, only half of the database. You need an MD and an LDF. And any additional NDF or secondary LDF files that composed the original database.

Suppose you have the MDF and the LDF as %1% and %3%, then all you have to do is execute this statement:

CREATE DATABASE [%2%] 
  ON (FILENAME=N'%1%')
  , (FILENAME=N'%3')
  FOR ATTACH;

See How to: Move a Database Using Detach and Attach (Transact-SQL)

The option to attach and MDF alone does exists (use FOR ATTACH_REBUILD_LOG) but it comes with many warnings, as it only works on a cleanly shut down database (it can lead to a corrupted database otherwise). There is no option to attach a database if you’re missing secondary NDF files.