Hi,

I work on a application which handles several (about 45) kinds of equipments.
All those equipments have common behaviors and are described in a hierarchy of classes with about 3 depth level.

I create a mapping file using joined-subclass because all thoses equipments have differents attributs and many-to-one associations.
I take care of number of levels in the mapping file removing all unecessary level (abstract class for exemples)

I use MySQL and when i try to get a set of equipments (which could contains any kind of equipments) a get the error "MySQL can only use 31 tables in a join". It's true have about 45 tables to join : all the kind of equipments.

The same mapping works with Oracle which accepts more than 31 tables in a join.

I set the hibernate property hibernate.use_outer_join to false to split the requests in part for many-to-one associations and I set the attribute "lazy" to true for one-to-many and many-to-many associations

But the problem still remains....
How can I decrease the number of joined tables ? Is there any attributs to set in the mapping file on the joined-subclass node ?

Help me !!! I don't want to break my object model to be pleased to a database ;-)

Florent