I was using Single Table mapping
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
It was working fine.

After I changed it to Table per class,
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)

I got the following exception when trying to loading data:

Exception in thread "HSQLDB Connection @170c7a3"
java.lang.ClassCastException: java.lang.Integer
at org.hsqldb.rowio.RowOutputBase.writeData(Unknown Source)
at org.hsqldb.Result.write(Unknown Source)
at org.hsqldb.Result.write(Unknown Source)
at org.hsqldb.ServerConnection.run(Unknown Source)
at java.lang.Thread.run(Thread.java:595)

I tried both MySQL and HyperSonic.
Any ideas? any help is appreciated.

Thanks, David

after changing @Inheritance, did you also make the appropriate changes in the data model?

Thanks!

It is running OK now with MySQL without any changes. I do not know how it happend. Maybe some table data were not cleaned up.


For table per class, if I use AUTO for id generation,
@Id(generate = GeneratorType.AUTO)

I got the following deployment exception:

org.hibernate.MappingException: Cannot use identity column key generation with <union-subclass> mapping for: example.Cat.

If I change it to Table:
@Id(generate = GeneratorType.Table)
It works fine.

All DBs support AUTO. For Table Per class, which one should I use? There are some others: Identity, sequence, none.

I tried to look for docs, none can be found on internet. The Javadoc
is really not very nice, no docs, just names. :-)

you cannot use identity that's all