Hibernate EntityCopyObserver: What Is It Used For?

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 […]

Hibernate Events and Custom EventListener Registration

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 […]

Is It Possible To Change Entity Fetch Strategy During Hibernate Merge?

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 […]

More about Eager Initialization of Lazy Associations During Hibernate Merge

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 […]

Hibernate Merge may Cause EAGER Initialization of LAZY OneToOne Associations

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) { […]

When It is Useful to Make Use of JPA @MapKey?

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 […]