JPA merge operation is used to reconnect and synchronize detached entities with active PersistenceContext so that changes performed on them could be reflected onto the database. Due to its complex nature, there might be times when multiple representations of an entity appears in the merge  process. Hibernate throws IllegalStateException in that case, because allowing each […]

Since Hibernate 3, each and every operation through Session API fires one or more persistence events during the course of its execution. For example, when you invoke session.get(Foo.class,1L), in order to fetch Foo entity with PK 1, Hibernate fires events with pre-load, load and post-load event types. There is a seperate EventListener interface for each […]

Hibernate needs to identify which entities in the Session has been changed, in other words become dirty in the meantime, so that it can issue an update sql statement to reflect those changes into the database. The default mechanism to identify dirty entities is to compare each attribute one by one with the snapshot kept […]

When I talk with my colleague about my experience with Hibernate merge behavior on lazy associations with cascade type merge, he suggested me to check if Hibernate allows us to change fetch logic it applies on detached entities during merge operation. That way, it would be possible to suppress eager initialization of those associations during merge. Hibernate […]

After reading my blog post about eager initialization of lazy 1:1 or M:1 associations because of the cascade merge attribute, someone asked about if it applies for 1:M and M:N associations as well? The answer is, yes it applies. Let’s create another small entity in order to illustrate that case as well. @Entity @Table(name=”T_BAZ”) public […]

Let’s have following two simple entities, having 1:1 lazy association between each other. @Entity @Table(name=”T_FOO”) public class Foo { @Id @GeneratedValue private Long id; @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.MERGE) @JoinColumn(name = “bar_id”) private Bar bar; public Long getId() { return id; } public Bar getBar() { return bar; } public void setBar(Bar bar) { […]

As you probably know, JPA provides way to map collection associations using java.util.Map. However, usage scenarios for such mappings are very limited; but when it comes, they become highly invaluable to easily extract necessary information from your domain model. They are especially useful in order to categorize entities in your associated collection based on some […]

  One of the undocumented features of Hibernate is its execution of SQL scripts given within a special file during bootstrap process. It is a very useful feature in order to populate your DB with sample data during testing or development mode. If you create a file named import.sql under project’s root classpath, and put […]