OK, I've just spent (quite literally) three hours reading the archives
(searched for all messages containing "inherit*" in them, and read them all!
{staggers out for coffee}) on the subject of inheritance (and the really
sad, sad, sad lack of it in the EJB 1.1 specification--what were they
*thinking*?), and now, hopefully better informed, I have a few questions.
I see from the archives that the only problems posed by an entity bean (E2)
inheriting from another entity bean (E1) are that an E1.findByPrimaryKey()
has no way of knowing (currently) if the reference returned is, in fact, a
reference to an E2 instance. I accept that there are hacks that one could
(quite easily! Why aren't they in the spec?!) use to get around this
problem--i.e. a discriminator column in each database table (
http://www.chimu.com/publications/objectRelational/
<http://www.chimu.com/publications/objectRelational/> ) coupled with
something like a getRemoteReferenceClass() method--but since they aren't
part of the specification (yet; they should be!), I don't want to use them.
OK, then. So I have this domain model, that actually doesn't use
inheritance *that* much, but does use it in a few of the standard and
extremely useful places. For example, I, probably like everyone else in the
world, have a Party class (has a name, contact information, an address book,
etc.) which is extended by an Individual class and an Organization class.
Parties can play Roles in Relationships, so, consquently, thanks to
inheritance, a NonProfitOrganization, for example, which extends
Organization and thereby Party, can play Roles as well.
Fine and good. Now I come to EJB, and I see that the specification does not
support inheritance in any way. Rrr.
Assuming that entity beans are the beasts of choice for most of the concepts
in my domain model (read the archives on that too; I recognize that not
every object in my domain model is by *default* a candidate for an entity
bean, but very few objects in my domain model are wholly contained by others
or are stateless), how can I map my domain model onto EJB constructs?
(I remember reading an article in the archives that suggested something
rather vague about "overlaying" an EJB construct "on top of" my domain
model, whatever that means. I believe that article could be rephrased much
less cloudily :-) by saying something like, "Entity beans do not always map
one-to-one with domain objects. Frequently, they can encompass several
domain objects. Of course, you need to make sure that the domain objects
that a given entity bean encompasses have the same types of lifecycle
issues." So that's not the question I'm asking.)
If this is a FAQ or is otherwise annoying :-) I'm happy to take this up with
someone via private email.
Cheers/Happy New Year to those to which it applies,
Laird
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