Hibernate application without writing sql query

sachin.kataria · **Joined:** Thu Jun 05, 2008 3:52 am **Posts:** 10

Hi,

I am using EntityManager with annotation based API for my hibernate application.

To persist data i am using entityManager.persist(object).

To retrieve records and to update records, i am using select queries and update queries on bean class (schemas) according to Entitmanager documentation.

But, i want to know, is there any other way to retrieve records with using only hibernate functionality (without queries) ?

I have to retrieve records without using primary key also. I must have to use annotations based API.

So, Is there any another way to fetch and update without writing sql query.

plesase help me.

hardy.ferentschik · **Posted:** Fri Jun 13, 2008 9:38 am

Hi,

Hibernate offers also the Criteria API which offers an object-oriented API for query creation. This is not part of the JPA specification though. If you have to stick to the JPA specs you will have to stick with EJB3-QL.

--Hardy

Cameron McKenzie · **Posted:** Fri Jun 13, 2008 11:36 am

The really great thing about the Hibernate Criteria API is that it allows developers to really look at their problems in an object oriented way. You think about what you need from your object model, not how to do a query to get what you want. This is great, as Java developers are notoriously bad at SQL and HQL.

So, for example, to find all users who have verified their password, you can use the Critieria API's Example object, and just execute code such as this:

Code:

 User user = new User();
    user.setVerified(false);
    Example example = Example.create(user);
    Session session = HibernateUtil.beginTransaction();
    Criteria criteria = session.createCriteria(User.class);
    criteria.add(example);
    List results = criteria.list();
    HibernateUtil.commitTransaction();
    for (int i = 0; i<results.size(); i++) {
      System.out.println(results.get(i).toString());
    }

As you can see, there is no HQL or SQL - just Java objects with various properties populated. It really is awesome.

I took this example from a little tutorial on the Hibernate3 Criteria API. If you'd like to take a look at those Hibernate examples, they're right here:

http://www.hiberbook.com/HiberBookWeb/learn.jsp?tutorial=09howtousethecriteriaapi

carlolf · **Posted:** Fri Jun 13, 2008 2:00 pm

Cameron McKenzie wrote:

This is great, as Java developers are notoriously bad at SQL and HQL.

I don't know if this statement is true. But I think, if you don't really understand SQL, you won't be a good Hibernate user and you should leave this job (in real projects) to someone who has this knowledge.

It is a general misunderstanding to think that ORM tools are a way to leave SQL and the database layer behind a Java facade.

Cameron McKenzie · **Posted:** Sun Jun 15, 2008 10:43 am

It's pretty rare to be on a project that has one person that is good at everything. And Java developers are just that, Java developers.

For every problem there is a tool, and Hibernate is a good tool for Java developers to leverage their existing skills and apply it to the data layer. Nothing wrong with that!

sachin.kataria · **Joined:** Thu Jun 05, 2008 3:52 am **Posts:** 10

Can we use merge() method of EntityManager to update records ?

i.e.

EntityManager entityManager = null;

//
//

entityManager.merge(user);

so, is it appropriate way to use merge() method ?

Cameron McKenzie · **Posted:** Wed Jun 18, 2008 10:11 am

Quote:

merge

public Object merge(Object object)
throws HibernateException

Copy the state of the given object onto the persistent object with the same identifier. If there is no persistent instance currently associated with the session, it will be loaded. Return the persistent instance. If the given instance is unsaved, save a copy of and return it as a newly persistent instance. The given instance does not become associated with the session. This operation cascades to associated instances if the association is mapped with cascade="merge".

From the Hibernate Session JavaDoc:

http://www.hibernate.org/hib_docs/v3/api/index.html

Speaking for the Hibernate Session, loading the entities should put them into the Hibernate Session cache, so they should already be managed by the Session during the current transaction. So, if you haven't comitted the transaction after getting the objects, you shouldn't need to merge. In fact, a saveOrUpdate call would probably suffice.