A Java geek

Hibernate is a widely-used ORM framework. Many organizations use it across their projects in order to manage their data access tier. Yet, many developers working on Hibernate don’t fully understand the full measure of its features. In this serie of articles, I will try to dispel some common misunderstandings regarding Hibernate.

Updating a persistent object

A widely made mistake using Hibernate is to call the update() method on an already persistent object :

session.getTransaction().begin();

Person person = (Person) session.load(Person.class, 1L);

person.setLastName("FooBar");

session.update(person);

session.getTransaction().commit();

This will get you the following Hibernate outputs :

Hibernate: select person0_.id as id0_0_,
    person0_.birthDate as birthDate0_0_,
    person0_.FIRST_NAME as FIRST3_0_0_,
    person0_.LAST_NAME as LAST4_0_0_ from Person person0_ where person0_.id=?
Hibernate: update Person set birthDate=?, FIRST_NAME=?, LAST_NAME=? where id=?

Now remove the line numbered 7. You get exactly the same output! If you check the database, the result will be the same: calling update() does nothing since the object is already persistent. If you are in debug mode, you can even check that the output’s update line is called when commiting the transaction in both cases.

You will find proof of this assertion here.

With new JEE 5 standard has come the EJB3 specifications. From an historical point of view, EJBs come into 3 different flavors: (i) Entity for persistence, (ii) Session for business logic and (iii) Message-Driven for listeners. Entity EJB are the most time-consuming to develop in their 2.1 version. Apart from the inherent complexity of EJB (local and remote interfaces, homes), developing an EJB 2 is error-prone because of the mapping mechanism. All in all, EJB 2 development really needs a very specialized IDE and expert developers. That’s the main reason why EJB 2 didn’t achieve a significant market share, and had to compete with JDO, Hibernate and other third-party frameworks.

Sun eventually realized this and did come with a much simpler solution with EJB 3. Using Java 5 annotations, developing Entity EJB 3 is a breeze. The part of EJB 3 specifications that deal with Entity is called Java Persistence API (JPA). It is a specification in its own right, and in the next specifications, it will have its own. Developing JPA applications is a two-step process. First, you have to create you model classes. Such classes will be the foundation of your persistence layer: it would be a good idea to use this layer throughout your entire organization, since these classes should closely map your database model. A simple JPA enhanced class would look like this: Read more…