Polymorphic results from a property of a queried object

asamir2 · **Joined:** Tue Apr 03, 2007 4:38 pm **Posts:** 3

I have a question related to the polymorphic queries.
I have a class hierarchy as the following:

Base class Cat
subclass AmericanCat extends Cat
subclass AsianCat extends Cat

I have another class called Master which has one to one relationship with the Cat using the catId foreign key

Hibernate version:
3.1

Name and version of the database you are using:
MS SQL Server 2005[/code]
Mapping documents:

Cat class hierarchy mapping:

Code:

<hibernate-mapping>
    <class name="Cat" table="Cat" schema="dbo" catalog="Test2">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="50" not-null="true" />
        </property>
        
        <property name="type" type="java.lang.String">
            <column name="discriminator" length="50" />
        </property>

        <joined-subclass name="AmericanCat" table="AmericanCat">
              <key column="catId" />
              <property name="americanName" type="java.lang.String" column="americanName"/>
        </joined-subclass>

        <joined-subclass name="AsianCat" table="AsianCat">
              <key column="catId" />
              <property name="asianPlace" type="java.lang.String" column="asianPlace"/>
        </joined-subclass>      
    </class>

The Master class mapping:

Code:

    <class name="Master" table="Master" schema="dbo" catalog="Test">
        <id name="masterId" type="java.lang.Integer">
            <column name="masterId" />
            <generator class="native" >
            </generator>
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="10" not-null="true" />
        </property>      
        
        <many-to-one name="cat" column="catId" unique="true" not-null="true"/> 
           
    </class>

When I perform a query like:

Code:

List masters = session.createQuery("from Master master where master.masterId='1'").list();
Master master = (Master)masters.get(0);
Cat cat = master.getCat();

System.out.println(cat.getId()); // This works fine.

//The following line generates a class cast excpetion although the selected
// cat is indeed of type AmericanCat.
System.out.println( ((AmericanCat)cat).getAmericanName());

I tested the polymorphic query using the "from Cat" and it works perfectly. The returned Cat super class can be casted to its original super class without problems . However, when I select the Master object, the superclass Cat property does not know its original subclass.

Any ideas if I am missing something or if there is any work around ?

Thanks in advance.

scesbron · **Joined:** Thu Sep 04, 2003 8:23 am **Posts:** 368

Maybe this is a proxy problem

Using hibernate proxy for classes (which is the default behaviour) with inheritance can lead to some problems but this is normally relative to instanceof tests.

Can you debug your app to see the class of your cat. Is it a proxy or not ? Are your sure this cat is an american cat ?

asamir2 · **Joined:** Tue Apr 03, 2007 4:38 pm **Posts:** 3

Thanks scesbron for the proxy hint.

I checked through the debugger and the returned cat reference was of type "Cat$$EnhancerByCGLIB$$28875802". It looks like a proxy as you have said.

Any idea how can we overcome this?

Thanks

scesbron · **Joined:** Thu Sep 04, 2003 8:23 am **Posts:** 368

Try setting lazy="false" on your cat mapping file

asamir2 · **Joined:** Tue Apr 03, 2007 4:38 pm **Posts:** 3

Thanks for the answer.
I have given you the point of this post.

Actually, I tried specifying the "lazy=false" at the relationship between the Master and the Cat in the Master mapping file and it worked as well.

I think this will disable the lazy fetching only for the Cats which are associated with the Masters instead of disabling it for all the Cats.

Thanks Again for the support