Hi,

I'm having a weird ClassCastException here. I have a many-to-many relationship between Category and Product. I create a Software, subclass of Product. When I retrieve a Category and get its Products (which are actually instances of the Software class), I actually get the CGLib enhanced class for Product (and not Software). Hence my ClassCastException when I try to cast to Software.

Actually when I do a toString() on one of the products I get a com.chooss.model.product.software.Software@e488b681 which looks fine. But when I do getClass.getName() I get com.chooss.model.product.Product$$EnhancerByCGLIB$$13db5343 which seems rather weird to me. And this thing can't be cast to a Software.

Hibernate version: 3.0.4

Mapping documents:
<hibernate-mapping>
<class name="com.chooss.model.product.Product" table="s_product">
<id name="id" column="id" type="java.lang.Long">
<generator class="native"/>
</id>
<discriminator column="disc"/>
<set name="categories" table="s_category_product" lazy="false">
<key column="fk_product"/>
<many-to-many class="com.chooss.model.product.Category"
column="fk_category"/>
</set>
....
<subclass name="com.chooss.model.product.software.Software"
discriminator-value="software">
...
</subclass>
</hibernate-mapping>
<hibernate-mapping>
<class name="com.chooss.model.product.Category" table="s_category">
<id name="id" column="id" type="java.lang.Long">
<generator class="native"/>
</id>
...
<set name="products" table="s_category_product" lazy="true">
<key column="fk_category"/>
<many-to-many class="com.chooss.model.product.Product"
column="fk_product"/>
</set>
</class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():
Category parent = categoryMgr.getCategory(parentLongId);
Set children = parent.getProducts();
ArrayList result = new ArrayList(softwares.size());
for (Iterator softIter = softwares.iterator(); softIter.hasNext();) {
Object obj = softIter.next();
System.out.println(obj);
// => com.chooss.model.product.software.Software@e488b681(id = 83)
System.out.println(obj.getClass().getName());
// => com.chooss.model.product.Product$$EnhancerByCGLIB$$13db5343
Software software = (Software) obj; // ClassCastException !!!!
}

Thanks for your help,

Matthieu.

Take a look at this section from the docs: http://www.hibernate.org/hib_docs/v3/reference/en/html_single/#performance-fetching-proxies. Seems to address what you are seeing.

I think you need to use the proxy attribute in your subclass.

Yet this article only refers to single-ended associations. In my case I have a many-to-many bidirectional relationship. Is it handled in the same way?

The docs don't say it directly, but I assume that DomesticCat interface extends Cat interface. So the question would be, in your case, if you had a Product interface and a Software interface that extends it, whether or not Hibernate retrieves the Category's Products as Softwares if they are actually Softwares. Seems like it should. I've never tried it, though. I'd be interested in hearing if it works.