Recordset: Locking Records (ODBC)

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This article applies to the MFC ODBC classes. For DAO recordsets, see the article DAO Recordset.

This article explains:

  • The kinds of record locking available.

  • How to lock records in your recordset during updates.

When you use a recordset to update a record on the data source, your application can lock the record so no other user can update the record at the same time. The state of a record updated by two users at “the same time” is undefined unless the system can guarantee that two users can’t update a record simultaneously.

****Note   ****This article applies to objects derived from CRecordset in which bulk row fetching has not been implemented. If you have implemented bulk row fetching, some of the information does not apply. For example, you cannot call the Edit and Update member functions. For more information about bulk row fetching, see the article Recordset: Fetching Records in Bulk (ODBC).

Record-Locking Modes

The database classes provide two :

  • Optimistic locking (the default)

  • Pessimistic locking

Updating a record occurs in three steps:

  1. You begin the operation by calling the member function.

  2. You change the appropriate fields of the current record.

  3. You end the operation — and normally commit the update — by calling the member function.

Optimistic locking locks the record on the data source only during the Update call. If you use optimistic locking in a multiuser environment, the application should handle an Update failure condition. Pessimistic locking locks the record as soon as you call Edit and doesn’t release it until you call Update (failures are indicated via the CDBException mechanism, not by a value of FALSE returned by Update). Pessimistic locking has a potential performance penalty for other users, since concurrent access to the same record may have to wait until completion of your application’s Update process.

Locking Records in Your Recordset

If you want to change a recordset object’s locking mode from the default, you must change the mode before you call Edit.

To change the current locking mode for your recordset

  • Call the member function, specifying either CRecordset::pessimistic or CRecordset::optimistic.

The new locking mode remains in effect until you change it again or the recordset is closed.

****Note   ****Relatively few ODBC drivers currently support pessimistic locking.

See Also   Recordset: Performing a Join (ODBC), Recordset: Adding, Updating, and Deleting Records (ODBC)