Pessimistic locking in Grails

We already know that by default Grails scaffold comes with Optimistic locking and it is achieved by version field. Now lets see how Pessimistic locking is achieved in Grails.
Grails has a built in method to acquire lock on object. To acquire a lock we will do something like following
[java]
Book book = Book.get(1)
book.lock()
[/java]
The above code will fire 2 queries one for getting the object and other for taking the lock on it, something like as follows
[java]
Hibernate: select book0_.id as id1_0_, book0_.version as version1_0_, book0_.name as name1_0_, book0_.price as price1_0_ from book book0_ where book0_.id=?
Hibernate: select id from book where id =? and version =? for update
[/java]
or we can do both the tasks in single go by using the static lock method
[java]
Book book = Book.lock(1)
[/java]
The above code will fire only one query
[java]
Hibernate: select book0_.id as id1_0_, book0_.version as version1_0_, book0_.name as name1_0_, book0_.price as price1_0_ from book book0_ where book0_.id=? for update
[/java]

Whenever there is simultaneous updations of an object occurs it throws StaleObjectException.

Hope it helps
Uday Pratap Singh
uday@intelligrape.com