Szerkesztés

Megosztás a következőn keresztül:

Recordset: Scrolling (ODBC)

  • Cikk

This topic applies to the MFC ODBC classes.

After you open a recordset, you need to access the records to display values, do calculations, generate reports, and so on. Scrolling lets you move from record to record within your recordset.

This topic explains:

Scrolling from One Record to Another

Class CRecordset provides the Move member functions for scrolling within a recordset. These functions move the current record by rowsets. If you have implemented bulk row fetching, a Move operation repositions the recordset by the size of the rowset. If you have not implemented bulk row fetching, a call to a Move function repositions the recordset by one record each time. For more information about bulk row fetching, see Recordset: Fetching Records in Bulk (ODBC).

Note

When moving through a recordset, deleted records might not be skipped. For more information, see the IsDeleted member function.

In addition to the Move functions, CRecordset provides member functions for checking whether you have scrolled past the end or ahead of the beginning of your recordset.

To determine whether scrolling is possible in your recordset, call the CanScroll member function.

To scroll

  1. Forward one record or one rowset: call the MoveNext member function.

  2. Backward one record or one rowset: call the MovePrev member function.

  3. To the first record in the recordset: call the MoveFirst member function.

  4. To the last record in the recordset or to the last rowset: call the MoveLast member function.

  5. N records relative to the current position: call the Move member function.

To test for the end or the beginning of the recordset

  1. Have you scrolled past the last record? Call the IsEOF member function.

  2. Have you scrolled ahead of the first record (moving backward)? Call the IsBOF member function.

The following code example uses IsBOF and IsEOF to detect the limits of a recordset when scrolling in either direction.

// Open a recordset; first record is current
CCustSet rsCustSet( NULL );
rsCustSet.Open( );

if( rsCustSet.IsBOF( ) )
    return;
    // The recordset is empty

// Scroll to the end of the recordset, past
// the last record, so no record is current
while ( !rsCustSet.IsEOF( ) )
    rsCustSet.MoveNext( );

// Move to the last record
rsCustSet.MoveLast( );

// Scroll to beginning of the recordset, before
// the first record, so no record is current
while( !rsCustSet.IsBOF( ) )
    rsCustSet.MovePrev( );

// First record is current again
rsCustSet.MoveFirst( );

IsEOF returns a nonzero value if the recordset is positioned past the last record. IsBOF returns a nonzero value if the recordset is positioned ahead of the first record (before all records). In either case, there is no current record to operate on. If you call MovePrev when IsBOF is already TRUE or call MoveNext when IsEOF is already TRUE, the framework throws a CDBException. You can also use IsBOF and IsEOF to check for an empty recordset.

For more information about recordset navigation, see Recordset: Bookmarks and Absolute Positions (ODBC).

When Scrolling Is Supported

As originally designed, SQL provided only forward scrolling, but ODBC extends scrolling capabilities. The available level of support for scrolling depends on the ODBC drivers your application works with, your driver's ODBC API conformance level, and whether the ODBC Cursor Library is loaded into memory. For more information, see ODBC and ODBC: The ODBC Cursor Library.

Tip

You can control whether the cursor library is used. See the bUseCursorLib and dwOptions parameters to CDatabase::Open.

Note

Unlike the MFC DAO classes, the MFC ODBC classes do not provide a set of Find functions for locating the next (or previous) record that meets specified criteria.

See also

Recordset (ODBC)
CRecordset::CanScroll
CRecordset::CheckRowsetError
Recordset: Filtering Records (ODBC)