[hibernate - jpa ] good practices and bad practices

Question

Hi all, i have some questions about interaction with hibernate.

1. openSession or getCurrentSession (without jta, thread insted)?

2. How mix session operations with swing gui? Is good have something like this in a javabean class?

   public void actionPerformed(ActionEvent event) {
       // session code
   }
   

3. Can i add methods to my entities that contains hql queries or is a bad practice? For example:

    // This method is in an entity MyOtherEntity.java class
    public int getDuration(){
       Session session=HibernateUtil.getSessionFactory().getCurrentSession();
       session.beginTransaction();
       int sum=(Integer)session.createQuery("select sum(e.duration) as duration from MyEntity as e where e.myOtherEntity.id=:id group by e.name").
           .setLong("id", getId());
           .uniqueResult();
       return sum;
    }
   

In alternative how can i do this in a better and elegant way?

UPDATE A widley used practice is made a service/dao class to achieve CRUD operation of our entites class. But WHY? Why i have to write a class for each my entities to manage it? Where is the real advantage?

UPDATE 2 Service class is a DAO pattern? Arthur Ronald F D Garcia's repository example is a DAO pattern, this is what called "service layer"?

Thanks.

Answer 1

If you want to rely on plain Hibernate API you can use a Service layer because

• It is Use case driven
• Delimit Transaction boundaries

So you can create a AccountService, for instance, like

public static path.to.HibernateUtil.getSessionFactory;

public class AccountService {

    public void withdraw(Integer accountNumber, BigDecimal amount) throws Exception {
        /**
          * Here you set up Transaction boundaries
          */
        getSessionFactory().getCurrentSession().beginTransaction();

        // Some actions goes here

        getSessionFactory().getCurrentSession().getTransaction().commit();
    }

}

You usually need a repository when performing some action inside your Service layer. You can Think of repository as a data provider and storage. Here you can see how i implement my repository.

If you want a maintainable and readable HQL query, I advice you externalize your HQL queries in a multline and externalized xml file

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"&gt;
<hibernate-mapping>
    <query name="GIFT_CARDS_WITH_BUYER">
        <![CDATA[
            from 
                GiftCard c
            left join fetch 
                c.buyer
            where
                c.recipientNotificationRequested = 1
       ]]>
    </query>
    <query name="GIFT_CARDS_WITHOUT_NO_RELATIONSHIP">
        <![CDATA[
            from 
                GiftCard
        ]]>
    </query>
</hibernate-mapping>

So inside your Swing GUI Event, you can call your service layer like

public void actionPerformed(ActionEvent event) {
    // Some related Swing GUI actions goes here (retrieve User input, validate data and so on...)

    accountService.withdraw(accountNumber, new BigDecimal(amount));
}

And it is not a good idea To use persistence actions inside your Entity. If you need to perform persistence related issues inside your Entity, I Think it is better you pass your repository as parameter to your Entity

public class Account {

   public void doSomething(AccountRepository repository) {
       // code goes here
   }

}

Maybe you want to see this Thread

I advice you Take a look at Java Persistence with Hibernate book, chapter 9 (Working with objects). ATT: read carefully

UPDATE

Why is good have a service layer ?

First of all

• It is Use case driven (It draws what your app should do)

Second of all

• It delimit Transaction boundaries

Suppose here goes your Service layer

public class MyService {

    public void doSomething() {
        getSessionFactory().beginTransaction();

        // A POJO doing some operation

        // Other POJO doing other operation

        // Another POJO doing another operation

        getSessionFactory().getTransaction().commit();
    }

}

Notice you just define one Transaction boundary instead of defining each one inside each POJO. And more, what happens whether your business rule inside your Swing GUI need to be used inside other component. Will you use a Ctrl-c + Ctrl-v ???