Hibernate Proxy Problem

Question

I'm sorry to ask such a basic question but I could not find a clear answer in others' questions:

I have a class Foo

public class Foo {
  private Integer id;
  private String name;
  private Bar bar;
  // getters and setters
}

And another class Bar

public class Bar {
  private Integer id;
  private String name;
  private Set<Foo> foos;

  // getters and setters 
}

I have a ManagedBean which has a ManagedProperty like this:

public class FooBean {
 @ManagedProperty(value = "{param.barId}"
 private Integer barId;
 private Bar bar;
 private Foo foo;

 public FooBean() {
 }

 @PostConstruct
 public void initialize() {
  SessionFactory factory = new Configuration().configure().buildSessionFactory();   
    if barId != null) {
      foo = new Foo();

      Session session = factory.openSession();

      try {
        session.beginTransaction();

        bar = (Bar) session.load(Bar.class, barId);        

        foo.setBar(bar);

        session.getTransaction().commit();
      } catch (Exception ex) {
        Transaction tx = session.getTransaction();
        if (tx.isActive()) {
          tx.rollback();
        }                
      } finally {
        session.close();
      }
    }
 }
}

And in my facelet I try to show the data thisway:

<h:outputText value="#{fooBean.foo.bar.name}" />

Which doesn't work! but If I add bar.getName() to my initialize method (after loading the bar) it works fine! Why? And what is a best practice alternative?

fmucar · Accepted Answer · 2011-01-11 15:54:02Z

3

add

lazy="false"

for the name property in your hibernate mapping xml.

answered Jan 11, 2011 at 15:54

fmucar

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1 Comment

ehsun7b Over a year ago

I didn't know that basic classes like Integer and String properties can be lazy! Thanks

Reboot · Accepted Answer · 2011-01-11 16:48:12Z

3

The problem is that you are using

session.load(...)

This method assumes that the entity exist. So it does not have to query the database to check and can simply return a proxy that will load the entity later. If you call a Getter method of the Bar object you will initialize the proxy and you can make other calls later without database access.

If you use

session.get(...)

this should not happen, because Hibernate will get the entity from the database immediately to check if it exists and does not return a proxy.

answered Jan 11, 2011 at 16:48

Reboot

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Comments

Bence Olah · Accepted Answer · 2011-01-11 16:05:35Z

1

You can do these:

Use eager initialization in your schema (if you use annotations then use 'fetch = FetchType.EAGER'), this defines that everytime a Foo instance is retreived from the DB Foo.bar will be fetched.
Write a jpa query which tells the API that foo.bar should be fetched in this query, something like this: 'From Foo foo join fetch foo.bar'

The first option is global, the second fetches the foo.bar for that query.

answered Jan 11, 2011 at 16:05

Bence Olah

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