I started using Hibernate3 and am getting the following exception:

org.hibernate.exception.GenericJDBCException: could not load an entity: [data.Entity#88]

Here is what I am trying to do. I have a Resource and Member classes, which extend the Entity class. Entity class contains entity_type column (which contains either "resource" and "member" strings), which I use as a discriminator in the <join> element similar to Gavin's example in http://blog.hibernate.org/cgi-bin/blosx ... 08/25#join.

The configuration files are loaded in the following order:
Entity.hbm, Resource.hbm, Member.hbm

In my test class I create and persist a Resource object and then I create and persist a Member object. After that I am trying to load the stored Resource object using EntityDAO.load(Long id) method. It works just fine and Hibernate checks the entity_type discriminator field, joins Entity and Resource table, loads the values and returns the right Resource object.

After this I am trying to load the stored Member object. However, for some reason Hibernate joins ALL three tables and then throws that exception above when trying to load the Member object. It seems that Hibernate does not check the discriminator field correctly in this case and joins all 3 tables.

Interestingly, if I switch the order of loading configuration files to:
Entity.hbm, Member.hbm, Resource.hbm and try to load stored Member object first it works fine, i.e. Hibernate joins just TWO tables Entity and Member and loads the Member object correctly. However, if after that I try to load the stored Resource object I get the error above.

It seems that my configuration is correct and Hibernate fails to load objects of the second subclass.

Any ideas?



P.S. Below is the complete stack trace:

org.hibernate.exception.GenericJDBCException: could not load an entity: [data.Entity#88]
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:82)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:70)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1142)
at org.hibernate.loader.EntityLoader.load(EntityLoader.java:111)
at org.hibernate.loader.EntityLoader.load(EntityLoader.java:97)
at org.hibernate.persister.BasicEntityPersister.load(BasicEntityPersister.java:2302)
at org.hibernate.event.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:352)
at org.hibernate.event.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:333)
at org.hibernate.event.DefaultLoadEventListener.load(DefaultLoadEventListener.java:158)
at org.hibernate.event.DefaultLoadEventListener.load(DefaultLoadEventListener.java:131)
at org.hibernate.event.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:193)
at org.hibernate.event.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:115)
at org.hibernate.impl.SessionImpl.load(SessionImpl.java:694)
at org.hibernate.impl.SessionImpl.load(SessionImpl.java:689)
at com.sww.calendar.data.base._BaseRootDAO.load(_BaseRootDAO.java:591)
at com.sww.calendar.data.base._BaseRootDAO.load(_BaseRootDAO.java:580)
at com.sww.calendar.data.base.BaseEntityDAO.load(BaseEntityDAO.java:36)
at com.sww.calendar.engine.CalendarTest.main(CalendarTest.java:63)
Caused by: org.postgresql.util.PSQLException: Result set not positioned properly, perhaps you need to call next().
at org.postgresql.jdbc1.AbstractJdbc1ResultSet.checkResultSet(AbstractJdbc1ResultSet.java:823)
at org.postgresql.jdbc1.AbstractJdbc1ResultSet.getString(AbstractJdbc1ResultSet.java:200)
at org.postgresql.jdbc1.AbstractJdbc1ResultSet.getFixedString(AbstractJdbc1ResultSet.java:792)
at org.postgresql.jdbc1.AbstractJdbc1ResultSet.getLong(AbstractJdbc1ResultSet.java:292)
at org.postgresql.jdbc1.AbstractJdbc1ResultSet.getLong(AbstractJdbc1ResultSet.java:506)
at org.hibernate.type.LongType.get(LongType.java:26)
at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:62)
at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:53)
at org.hibernate.type.AbstractType.hydrate(AbstractType.java:70)
at org.hibernate.persister.BasicEntityPersister.hydrate(BasicEntityPersister.java:1521)
at org.hibernate.loader.Loader.loadFromResultSet(Loader.java:802)
at org.hibernate.loader.Loader.instanceNotYetLoaded(Loader.java:760)
at org.hibernate.loader.Loader.getRow(Loader.java:671)
at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:278)
at org.hibernate.loader.Loader.doQuery(Loader.java:366)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:193)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1133)

After a little more investigation I found out that Hibernate seems to map the table of the superclass to the first loaded subclass configuration. So, if Resource.hbm is loaded first, then Hibernate will always select fields of the Resource table when running queries against Entity table.

So, if Resource.hbm is loaded before Member.hbm and an entity with entity_type "resource" is found, then Hibernate maps it correctly to an object of the Resource class. However, if an Entity with entity_type "member" is found, then Hibernate joins all 3 tables, selects the fields of the Resource table and tries to map them to an object of the Member class. Hence, the JDBC result set exception.

Is this a Hibernate bug or smth silly on my part?

Thanks.

Can you provide more informations ie:
- a small working testcase
- the hbms
- etc

I sent you an email at emmanuel@hibernate.org with a zipped Eclipse project.

Thanks.

Alec

it's not a good way....

please, use this forum and the code tag when showing sources.

Come on, it's christmas, you gave me a 300k project ;-)
Honnestly I can't spend too much time, the problem has to be isolated (3 classes and a runnable test case) and posted to JIRA.
If you really can't, at least post it to JIRA with a simple description, one of ours will try to have a look.

Sorry, I forgot about the Christmas thing. I'll resend it to you after the New Years then ;)

Seriously, I will try to isolate the problem to 3 classes and post to JIRA. I'll let you know when it's done.

Thanks.