Hi Folks,

I have a schema that represents an online shop, where Products belong to exactly one Category, and each Category contains a collection of Products that belong to it. The Product table has a categoryid column, and the category - product mapping is carried out via a pivot table called 'category_products'.

A LazyInitializationException occurs when I try to get a Product from the database by id because, when constructing the Product instance, hibernate is calling Product's setCategory method, which is trying to add a reference to itself inside Category's 'products' collection, however the collection hasn't yet been initialized. I've tried adding lazy="false" to the mapping entry for the 'products' collection, but this didn't seem to have an effect. I've also tried enabling eager fetching on this collection (using outer-join="true") but this didn't work either.

I'm actually not keen on pulling all of the Products belonging to a particular Category out of the database when I only want to get 1 product from that Category, so perhaps I'm going about this in the wrong way.

Do you guys have any ideas?

Cheers,
Richard.

Hibernate version:

3.1.3

Mapping documents:

Category.hbm.xml
============

[...]

<set name="products" lazy="false" cascade="all-delete-orphan" table="category_products">
<key column="categoryid"/>
<many-to-many column="productid" class="uk.co.plugandplaydesign.core.dal.hibernate.Product"/>
</set>

[...]

Product.hbm.xml
===========

[...]

<many-to-one name="category" cascade="none" column="categoryid" class="uk.co.plugandplaydesign.core.dal.hibernate.Category"/>

[...]

Code between sessionFactory.openSession() and session.close():

Essentially, it's just creating and running this query -

HibernateUtil.currentSession(hibernateConfig).createQuery("from Product where id = '2'");

Here's the setCategory method in Product that's causing the trouble -

public void setCategory(Category category) {
if (this.category != null) {
//if the product already belongs to a category, remove
//the reference
this.category.getProducts().remove(this);
}

this.category = category;
if (this.category != null) {
category.getProducts().add(this); // (1)
}
}

// (1) the collection returned by category.getProducts() hasn't been
// initialized at this point for some reason

Full stack trace of any exception that occurs:

227-Dec-2006 10:56:05 org.hibernate.LazyInitializationException <init>
SEVERE: illegal access to loading collection
org.hibernate.LazyInitializationException: illegal access to loading collection
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:341)
at org.hibernate.collection.AbstractPersistentCollection.write(AbstractPersistentCollection.java:183)
at org.hibernate.collection.PersistentSet.add(PersistentSet.java:165)
at uk.co.plugandplaydesign.core.dal.hibernate.Product.setCategory(Product.java:211)
at sun.reflect.GeneratedMethodAccessor81.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:42)
at org.hibernate.tuple.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:330)
at org.hibernate.tuple.PojoEntityTuplizer.setPropertyValues(PojoEntityTuplizer.java:188)
at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:3232)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:129)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:842)
at org.hibernate.loader.Loader.doQuery(Loader.java:717)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.loadCollection(Loader.java:1919)
at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:36)
at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:520)
at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60)
at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1676)
at org.hibernate.collection.AbstractPersistentCollection.forceInitialization(AbstractPersistentCollection.java:454)
at org.hibernate.engine.StatefulPersistenceContext.initializeNonLazyCollections(StatefulPersistenceContext.java:755)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:229)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:375)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:308)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:153)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1106)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
at uk.co.plugandplaydesign.core.dal.HibernateUtil.executeQuery(HibernateUtil.java:39)
at uk.co.plugandplaydesign.core.dal.HibernateUtil.executeQuery(HibernateUtil.java:44)
at uk.co.plugandplaydesign.core.dal.HibernateUtil.executeQuery(HibernateUtil.java:27)
at uk.co.plugandplaydesign.core.dal.PersistenceHandler.getEntities(PersistenceHandler.java:111)
at uk.co.plugandplaydesign.core.dal.PersistenceHandler.getSingleEntity(PersistenceHandler.java:94)
at uk.co.plugandplaydesign.core.dal.dao.ProductDAO.getShallowProduct(ProductDAO.java:184)
at uk.co.plugandplaydesign.core.dal.dao.ProductDAO.getProduct(ProductDAO.java:189)
at uk.co.plugandplaydesign.dal.dao.AbstractPersistenceTestFixture.tearDown(AbstractPersistenceTestFixture.java:185)
at uk.co.plugandplaydesign.dal.dao.ProductPersistenceTest.tearDown(ProductPersistenceTest.java:62)
at junit.framework.TestCase.runBare(TestCase.java:136)
at junit.framework.TestResult$1.protect(TestResult.java:110)
at junit.framework.TestResult.runProtected(TestResult.java:128)
at junit.framework.TestResult.run(TestResult.java:113)
at junit.framework.TestCase.run(TestCase.java:120)
at junit.framework.TestSuite.runTest(TestSuite.java:228)
at junit.framework.TestSuite.run(TestSuite.java:223)
at org.junit.internal.runners.OldTestClassRunner.run(OldTestClassRunner.java:35)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:38)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)


Name and version of the database you are using:

Postgres 8.1

As i uderstand, you have many-to-one association from Product to Category and one-to-many association from Category to Product. Why you have link table category_products and define this association as many-to-many? This kind of association implies that both sides of association are collection valued, i.e. Product may belong many Categories and Category may have many Products. This isn't your case, right? Sorry, if i don't understand the problem.

Well, it seems I probably was going about this the wrong way. I guess writing out that message helped me realise that what I was trying to do didn't really make sense.

I've now made the Product.setCategory package private, and if I want to add a Product to a Category, I'm just invoking the Category.addProduct method.

Cheers,
Richard.