One of the fundamental principles of Hibernate/JPA is that any writes done through the Session/EntityManager APIs are collected in the persistence context and are only written to the database upon transaction commit. If needed, you can enforce the flushing of changes by explicitly invoking the flush() method. Also Hibernate may trigger a flush automatically, e.g. prior to executing a query. This strategy allows to perform many optimizations, e.g. only persisting the final state of an entity changed several times, make use of batched inserts and others.
