Hibernate version:
3.0.1

Mapping documents:
table-per-hierarchy mapping (three subclasses)

I (mistakenly) tried to load a class using another subclass's key, and got an instance back, of the wrong type.

E.g. I have classes X, Xa, Xb and Xc, where X is the superclass of the other three, I map them all to one table and perform

Xb xb = ...
Session s =...
Xa xa = s.get(Xa.getClass(), xb.getId());

and I get an Xa instance back holding xb's data. (The DB correctly stored the xb instance with the discriminator tag indicating it is an instance of Xb.)

If this is not a known issue, either bug it or let me know and I'll bug it.

Also using v3.0.1

Session.load(Class c, Object k) is behaving the same way.

In my case, Client and Partner both subclass Person and are declared with descrimiators and Person is defined with polymorphism="explicit"

Did anybody figure this out ?. I am also having similar problem.

I have Xa and X Xa is the subclass of X. I am try to get Xa, by passing Xa.class Here if Xa does not exist,but X exist.I am getting an instance of X. insted of a WrongClassException.

I should have mentioned that there is a workaround -- query using the superclass (abstract superclass is ok) and check that the object is what you really want. Querying using the abstract class correctly uses the discriminator to instantiate the proper class in our case.

Inefficient, but will work.



As always, adding isXb() isXa() etc. methods is cleaner.

Finding the subclass object with Superclass type works fine.

But if I am interested only in the subclass, I should be able to find it by
get(XSub.class, myKey). Here if a record exist for XSub, It should return the instance, otherwise, a null or exception.

I have opened the following JIRA issue:

http://opensource.atlassian.com/project ... se/HHH-416

As you will see if you monitor this issue in JIRA...

According to Gavin...
"This is not a bug and has been the behavior of every version of Hibernate ever. "

So I guess we'll have to live with this behavior.

That means, If we use Hibernate to map an inheritance relation using table per hierarchy strategy , We should never use 'get' or 'load' methods with subclass type ?.

Consider the following situation:

Person inherits from Employee. I have a method terminate() in Employee class. I have a person Id and find the employee with that person Id and terminate him.(Finding the employee with person Id because this is a table per hierarchy mapping and the primary Key is person Id for both Person and Employee)

I would like to find an Employee by personId and call terminate().Instead of finding a Person , and check whether he is an employee then call terminate()

You are completely misunderstanding the contract of get/load.

The contract is:

* I have an id which is the id of an instance of Subclass.
* get me that instance

If you want some other contract, use a query!

But in a table per hirarchy mapping, both Subclass and superclass will have the same Id colum in database right ?.

I am sorry, I made a mistake in the previuos post.

"Consider the following situation:

Person inherits from Employee. " is wrong.

Employee inherits from Person..

I used find("select query by person Id")

public Employee findEmployeeByPersonId(Long persontId){
List employees = null;
employees = getHibernateTemplate().find("from Person per where per.personid = ?",new Object[] {persontId});
if(!employees .isEmpty())
return (Employee)members.get(0);
else
return null;
}

Here , if If I pass a personId who is not an Employee, I am getting Class cast exception which means Hibernate is creating the Correct class "Person".

I feel that Hibernate's behaviour here is not intuitive.

The use case is strange as it seems backward that one would have an id and then try looking up the wrong subclass, however I feel that Hibernate's behaviour of coercing the object into the wrong subclass when given an ID of a different subclass is not the expected behavior.

The discriminator mapping for each subclass has been specified in the mapping while so when looking up an on object using code like one one below, the first filter that should take place should be that of the discriminator value followed by the user specified id.



Sanjiv