Connection Object

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[oR]

In the previous ADO code samples a connection to the database has been specified using a connection string, and this is passed to, for example, the _RecordsetPtr::Open function. This may seem quite inefficient, since it appears that a new connection to the database is made each time a recordset is opened. As it happens, ADO caches connections and so re-uses an existing connection rather than making a new connection each time. However, it can be convenient to create a connection using a _ConnectionPtr interface. For example, the _ConnectionPtr interface allows SQL statements to be executed directly whether they return a result set or not. A good example of this is the SQL DELETE statement.

Once a _ConnectionPtr interface has been obtained through calling CreateInstance, the Open function can be called to make a connection to the database. This function is passed the following:

• A standard connection string

• A user name (not required by SQL Server for Windows CE)

• A password (not required by SQL Server for Windows CE)

• Options, which should be passed as 0

The following code shows a function called GetConnection that returns a connection to the database used in previous code examples.

 BOOL GetConnection(AdoNS::_ConnectionPtr & pConnection) {   HRESULT hr;   _bstr_t bstrConnection(lpConnection);   _bstr_t bstrUserID(_T(""));   _bstr_t bstrPassword(_T(""));   hr = pConnection.CreateInstance         (_T("ADOCE.Connection.3.1"));   if(FAILED(hr))   {      cout   _T("Could not create connection:")             hr   endl;      return FALSE;   }   hr = pConnection->Open(bstrConnection,           bstrUserID, bstrPassword, 0);   if(FAILED(hr))   {      cout   _T("Could not create connection:")             hr   endl;      return FALSE;   }   return TRUE; } 

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