def book = Book.get(1) book.lock()
lock method obtains a pessimistic lock using an SQL
select … for update.
lock method obtains a pessimistic lock on an instance, locking the row in the database with
select … for update. The
lock method is equivalent to using Hibernate’s LockMode.UPGRADE in combination with the http://docs.jboss.org/hibernate/orm/current/javadocs/org/hibernate/Session#lock(java/lang/Object, org/hibernate/LockMode).html[lock] method.
The lock is automatically released when the transaction commits. In Grails this is typically after an action has finished executing.
Refer to the section on Optimistic and Pessimistic locking in the user guide for info.