Join inheritance type issue

bytec0de · **Joined:** Fri Jul 28, 2006 2:31 pm **Posts:** 4

Hi,

Should the find method of entity manager return null if a subclass is not found (although the instance exists in the base class)?

Let me explain better. I have the following entities:

Code:

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class BaseClass implements Serializable {
   @Id
   @GeneratedValue(strategy=GenerationType.AUTO)
   private int id;
   
   @Basic
   private String text;
   
   public BaseClass() {   
   }
   
   public BaseClass(String text) {
      this.text = text;      
   }
   
   public int getId() {
      return id;
   }
   
   public String getText() {
      return text;
   }   
}

@Entity
public class B extends A {
   @Basic
   private String extraText;

   public B() {      
   }
   
   public B(String baseText, String extraText) {
      super(baseText);
      this.extraText = extraText;
   }

   public String getExtraText() {
      return extraText;
   }
}

Next I create to records.

Code:

A a = new A("some text");
manager.persist(a);
int id1 = a.getId();
B b = new B("some text", "another extra text");
int id2 = b.getId();

// Try to locate a B instance with id1
// Should return null but instead it returns ClassCastException
b = manager.find(B.class, id1);

My question is: shouldn't the last line returns null instead of ClassCastException. The specification states that the find method returns null if no instance of type B exists in the persistence store. But in the above code it returns an A instance instead of null (and the consequent ClassCastException)...

I checked the SQL generated by Hibernate and it seems that for the Joined inheritance type it uses a Left Outer Join. Shouldn't be a Inner Join instead?

Best regards,

Vítor Carreira

PS. Using hibernate 3.2.0.cr4 / hibernate EM 3.2.0CR2 / postgresql 8

emmanuel · **Posted:** Mon Oct 09, 2006 4:50 pm

I like the current behavior. It avoids hidden application bugs

bytec0de · **Joined:** Fri Jul 28, 2006 2:31 pm **Posts:** 4

I'm sorry but I don't share the same opinion. If I want to locate a specific instance of type B using the find method of the EntityManager, using the current Hibernate implementation I must surround the code in a try-catch block looking for a ClassCastException (instead of testing for a clean null return value).

I can't see the kinds of bugs avoided using the current approach...

But thanks for replying. At least I known it was an option maded by the hibernate team and not a "bug".

Best regards,

Vítor Carreira