Hi
Matthias,
that's right, but I can build an inheritance structure for the matching
value objects, too.
An
AnimalService session bean can coordinate the calls to the CatHome and the
DogHome and return an AnimalValue
which means a DogValue object or a CatValue object. So the only problem
is, that the inheritance structure is fixed in the
service class and I cannot easily extend it only by adjusting the
AnimalService. To make it extensible one may use a kind
of
server side factory pattern, so the AnimalService can load its concrete bean
home classes from a config file. So this information
is
very helpful for me.
Can
you tell me, what happens in case of an EJB inheritance? Is it only an
inheritance of the remote interfaces from eachother
(Cat
extends Animal, Dog extends Animal) and the bean classes (DogBean and CatBean
extend AnimalBean) or happens
something additionally?
Something to the point, that I cannot cast ... Is there really no
possibility? Why can I not cast beans? Even not if I
implement
the
ejbLocateHome like this?
public
BaseCustomer ejbHomeLocate(String customerID) throws FinderException
{
//At this point, all base EJB classes must know their
EJB subclasses...
Context jndiCtx;
BaseCustomerHome bHome;
GoldCustomerHome
gHome;
PlatinumCustomerHome pHome;
try {
jndiCtx = new
InitialContext();
bHome =
(BaseCustomerHome)ctx.getEJBLocalHome();
gHome =
(GoldCustomerHome)jndiCtx.lookup("GoldCustomerEJB");
pHome =
(PlatinumCustomerHome)jndiCtx.lookup("PlatinumCustomerEJB");
} catch (NamingException e) {
throw new
FinderException("Cannot obtain JNDI initial context.");
}
BaseCustomer b=null;
try
{
b =
bHome.findByPrimaryKey(customerID);
return
b;
} catch (FinderException e) {
}
try {
b =
gHome.findByPrimaryKey(customerID);
return
b;
} catch (FinderException e) {
}
try {
b =
pHome.findByPrimaryKey(customerID);
return
b;
} catch (FinderException e) {
}
throw new FinderException("Cannot find any bean with
that key.");
}
Bye
and have a nice weekend
Thorsten
Hi Thorsten,
next week, there will only be a maintenance release (2.1.1) that
fixes the build.xml bug in the empty sample project wizard for Hibernate 2
projects. Support for abstract EJB inheritance is already in the code base
of AndroMDA 3.x (see the HEAD branch in CVS). You may try it already if you
do a CVS checkout and build AndroMDA from the sources which is only a matter
of one line in a properties file and a call to "ant".
About EJB inheritance: There is no REAL inheritance in EJB. For
example: Create three beans, call them AnimalBean, DogBean and CatBean. Let
DogBean and CatBean inherit from AnimalBean. Let all the interfaces inherit,
too. Then, call DogHome.create("fido") and CatHome.create("pussy"). Then,
call AnimalHome.findByPrimaryKey("fido"). Surprise, surprise: You will get
an AnimalBean, not a DogBean and you will NOT be able to cast. You see what
happened?
So all that we do in the AndroMDA 3.x EJB cartridge is abstract
inheritance. The base classes themselves cannot create instances and cannot
find instances of derived classes.
Cheers...
Matthias
Hi Matthias,
you talked about a new release next week.
Is the support for EJB inheritance inside this
release?
Someone told me you are working on this ...
For the value objects I adjusted the VSL file to solve this
problem.
I think it is more difficult for the entity bean classes, because
of the home interface, isn't it. In an article about this
inheritance problem I read that one have to implement ejbHomeLocate methods in the base bean class to
reference
the subclass beans. Is that right?
Cheers
Thorsten
