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Have gone through hibernate api specification on FlushMode but didn't get the exact difference. So please help.
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java.lang.Object org.hibernate.FlushMode All Implemented Interfaces: Serializable public final class FlushMode extends Object implements Serializable. Represents a flushing strategy. The flush process synchronizes database state with session state by detecting state changes and executing SQL statements.
You need to flush in batch processing otherwise it may give OutOfMemoryException. Commit(); Commit will make the database commit. When you have a persisted object and you change a value on it, it becomes dirty and hibernate needs to flush these changes to your persistence layer.
Flushing is the process of synchronizing the state of the persistence context with the underlying database. The EntityManager and the Hibernate Session expose a set of methods, through which the application developer can change the persistent state of an entity.
If you want to use the FlushModeTypes AUTO or COMMIT, which are defined by the JPA specification, you can call the setFlushMode method on your Query or TypedQuery interface. Query q = em. createQuery( "SELECT p from ChessPlayer p" ); q.
If flush mode is 'AUTO' before firing any query hibernate will check if there are any tables to be updated. If so, flush will be done otherwise no. If flush mode is 'ALWAYS', flush will happen even if there are no tables to be updated.
Check source of , org.hibernate.event.def.DefaultAutoFlushEventListener.onAutoFlush(AutoFlushEvent)
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Always means that before any query is run on a collection or such the query is rerun against the database. With auto I am assuming there is some "magic" under the hoods that knows most data doesn't change that often so you don't always have to flush. It also affects how often might happen during a transaction. I say might because some sources say setting the flushmode is only a hint to hibernate - but see this thread for some discussion...
http://forum.springsource.org/archive/index.php/t-14044.html
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