Hibernate自引用关系和延迟加载

Question

Before asking the question, here is the context of my problem:

I got a specific entity named 'Category', which have a property Category (a parent) and another property of type 'relatedEntity'.

Here is a sample of the code:

@Entity
public class Category {

    ...

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="entityID")
    private RelatedEntity entity;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="parentID")
    private Category parent;

    ...
}

So, as you can see, I've declared ManyToOne relationships for these properties, and also a lazy loading fetching strategy.

Now, I use this method inside a DAO object to get a list of Category:

public List<Category> getAll() {
    Criteria crit = sessionFactory.getCurrentSession().createCriteria(Category.class);
    return (crit.list());
}

I got a specific service object which calls the DAO method:

@Transactional(readOnly = true)
public List<Category> getAllCategories() {
    return (categoryDAO.getAll());
}

Nothing really extraordinary for the moment... Now, here come my unit tests:

@Test
public void testCategories() {

    List<Category> cat = service.getAllCategories();
    assertNotNull(cat);
    assertFalse(cat.isEmpty());

    for (Category c : cat) {

        try {
            assertNotNull(c.getEntity().getName());
            fail("Expected lazy init. on Category.Entity");
        }
        catch(LazyInitializationException ex) {
             //Exception is caught
        }

        try {
            assertNotNull(c.getParent().getName());
            //No exception
            fail("Expected lazy init. on Category.Parent");
        }
        catch(LazyInitializationException ex) {}
    }
}

After running the test, an exception is catched in the first try/catch block and the second fail is fired, saying that there is no LazyInitException on the parent property of the category.

So I can call

c.getParent().getParent().getName(); 

or

c.getParent().getParent().getParent().getName() 

without any exception being raised.

I've set 'show_sql=true' in my configuration file, I can't see any supplementary request in my logs after calling the getter on the parent property, so there is no new request but the parent property is loaded.

Can somebody explain me why the parent property is not lazy?

EDIT:

I've updated my test case.

@Test(expected=LazyInitializationException.class)   
public void lazyCategoriesParentsList() {
    List<Category> cat = service.getAllCategories();

    assertNotNull(cat);
    assertFalse(cat.isEmpty());

    for (Category c : cat) {            
        assertNotNull(c.getParent().getName());     
    }       
}

And now the test is passing... Was it related to the access of the entity property (via c.getEntity()) in my previous test case?

Answer 1

Could you try getting only one Category instead of loading them all ?

Indeed, when you are loading a Category , if hibernate can find its parent in the same Session , it will initialize it, even if parent is marked as lazy. As you are querying for all categories, it will find all the parents in the Session and initialize them.