Recordset: Bookmarks and Absolute Positions (ODBC)
This topic applies to the MFC ODBC classes.
When navigating through a recordset, you often need a way of returning to a particular record. A record's bookmark and absolute position provide two such methods.
This topic explains:
A bookmark uniquely identifies a record. When you navigate through a recordset, you cannot always rely on the absolute position of a record because records can be deleted from the recordset. The reliable way to keep track of the position of a record is to use its bookmark. Class CRecordset supplies member functions for:
Getting the bookmark of the current record, so you can save it in a variable (GetBookmark).
Moving quickly to a given record by specifying its bookmark, which you saved earlier in a variable (SetBookmark).
The following example illustrates how to use these member functions to mark the current record and later return to it:
// rs is a CRecordset or // CRecordset-derived object CDBVariant varRecordToReturnTo; rs.GetBookmark( varRecordToReturnTo ); // More code in which you // move to other records rs.SetBookmark( varRecordToReturnTo );
You do not need to extract the underlying data type from the CDBVariant Class object. Assign the value with GetBookmark and return to that bookmark with SetBookmark.
Depending on your ODBC driver and recordset type, bookmarks might not be supported. You can easily determine whether bookmarks are supported by calling CRecordset::CanBookmark. Furthermore, if bookmarks are supported, you must explicitly choose to implement them by specifying the CRecordset::useBookmarks option in the CRecordset::Open member function. You should also check the persistence of bookmarks after certain recordset operations. For example, if you Requery a recordset, bookmarks might no longer be valid. Call CDatabase::GetBookmarkPersistence to check whether you can safely call SetBookmark.
Besides bookmarks, class CRecordset allows you to set the current record by specifying an ordinal position. This is called absolute positioning.
Absolute positioning is not available on forward-only recordsets. For more information about forward-only recordsets, see Recordset (ODBC).
To move the current record pointer using absolute position, call CRecordset::SetAbsolutePosition. When you pass a value to SetAbsolutePosition, the record corresponding to that ordinal position becomes the current record.
The absolute position of a record is potentially unreliable. If the user deletes records from the recordset, the ordinal position of any subsequent record changes. Bookmarks are the recommended method for moving the current record. For more information, see Bookmarks in MFC ODBC.
For more information about recordset navigation, see Recordset: Scrolling (ODBC).