Inheritance in EJBs

Question

I am trying to find out if Weblogic supports functionality that TOPLink provides to
represent inheritance.
(http://www.webgain.com/products/toplink/mapping_workbench/demos/
check the "Using Advanced Descriptor Functions", "Inheritance").
I want to have a parent class which has multiple children (i.e. an Account class,
subclasses as Checking, Savings, Loan, etc.). These would all be stored in one database
table. A single 'findAccountsForCustomer' method could return a mixed collection
of the specific child objects.
Is this something available in a current version of Weblogic, or something planned
for the future? Or, is this something that requires a 3rd party mapping tool?

Answer 1

How does this differ from the second option I listed?
Thanks,
Bob
"Nick Minutello" <[email protected]> wrote
in message news:[email protected]...
>
>
You can achieve inheritance using Entity Beans. Its not the simplest ofthings -
but its do-able. (Although I will admit I havent done this for aproduction application).
>
You would create an AccountBean - which is the base-class implementation.Your other
Checking, Savings, Loan Beans inherit from it. (Strictly they dont haveto - this
is only so you have implementation inheritance.)
Then, you would also create an AccountLocal - which is the base-classcomponent interface.
Your other CheckingLocal, SavingsLocal, LoanLocal Interfaces inherit fromit. (this
is so you get polymorphism at the client level)
Your PK classes must be the same all. (though, I forget why at the moment)
You need to create a home for each Bean (this makes sense - you have tohave a factory
that knows what its creating/finding).
You need to list all of them in the DDs. (the CMP mapping duplication is apain)
>
Its all a bit dicky doing it by hand. But if you can get your hands onWSAD4, it
will automate this all for you (Sadly, it only supports EJB1.1.... but youcan see
how it does it)
The thing to remember is that if they are in the same table (I wouldreconsider that
decision) then your findByPrimaryKey method will never be able todistinguish between
them.
The finders are a bit tricky - you need to do the aggregation of thesub-types.
>
-Nick
"Bob Lee" <[email protected]> wrote:
EJB does not support inheritance. You are limited to standard Java's
inheritance capabilities.
If you want to use entity beans, you have the following two options:
1) Have a generic Account entity bean with an account type field (rather
than subclassing).
2) Use Java inheritance, set up an entity bean for each type (Savings,
Checking, etc.) and use a session facade. The findAccountsForCustomer()
method in the session facade will hit each entity bean type and combine
the
results.
I would probably go with the first option. You can use the Strategy
pattern
or something comparable to handle the implementation differences between
the
Account types.
Bob
"Howard Webb" <[email protected]> wrote in message
news:[email protected]...
I am trying to find out if Weblogic supports functionality that TOPLinkprovides to
represent inheritance.
(http://www.webgain.com/products/toplink/mapping_workbench/demos/
check the "Using Advanced Descriptor Functions", "Inheritance").
I want to have a parent class which has multiple children (i.e. an
Account
class,
subclasses as Checking, Savings, Loan, etc.). These would all be
stored
in one database
table. A single 'findAccountsForCustomer' method could return a mixedcollection
of the specific child objects.
Is this something available in a current version of Weblogic, or
something
planned
for the future? Or, is this something that requires a 3rd party
mapping
tool?
>