You need to decide on which is the most effective locking strategy in your
case. The options are optimistic locking (no locks), pessimistic locking
(edited record) and table locking (all records). You usually only need
consider the first two in the context of users inputting data via forms.
Optimistic locking allows more than one user to concurrently edit the same
record. If a record being edited by one user is edited and saved by a second
user then a write conflict occurs. The first user is alerted to this when
they attempt to save the record and is given the opportunity of (a) saving
the record, in which case they overwrite the second user's changes; (b)
copying the changes to the clipboard and refreshing the record with the
second user's changes; (c) dropping the changes , in which case the record is
refreshed with the second user's changes.
Pessimistic locking immediately locks a record as soon as one user starts to
edit it, so another user is prevented from making any changes until the
record has been saved and thus unlocked. A user viewing the locked record
will see a circle with a diagonal bar across it in the record selector bar on
the left of the form.
Optimistic locking used to be the most popular despite its drawbacks as, in
early versions of Access, a complete 'page' of data was locked by pessimistic
locking, which could be several records, not just the current one. Nowadays
pessimistic locking is usually favoured as only the current record per se is
locked.
You can set the default locking strategy in the Advanced tab of the Options
dialogue (Tools | Options on the main database menu bar – in Access 2003 at
least, it might differ in later versions). In forms you can set the form's
RecordLocks property in the properties sheet.
Ken Sheridan
Stafford, England
