Hi Matt,
Excuse me to jump in here, but I believe what you have in mind is not
possible in Java and even less with OJB. If your B1 and B2 instance
should 'contain' the same A instance as base class, they are identical
objects, which would require a language that supports multiple
inheritance (and virtual base classes). You could do that in in C++
but not in Java.
What you can do in Java (and OJB) is declare an interface I_A
implemented by A, B1 and B2. I_A just declares all public methods of A
and in B1 and B2 you implement this interface by delegation. That is
in B1 and B2 you have a reference to a A object and all I_A methods on
B1 and B2 are just routed to this reference. That way distinct
instances of B1 and B2 can easily share a common A reference.
HTH,
Gerhard
On Tue, 21 Oct 2003 00:27:02 -0400, Matt Mastrangelo
<[EMAIL PROTECTED]> wrote:
>Chris,
>
>Just to clarify -- are you saying it's not possible to create the User
>instance without also creating a new Person instance? Maybe my example
>was not too clear. Let me re-explain:
>
>I have a base class A with two subclasses, B1 and B2. I have already
>created an instance of B1 and stored it to the database, which means
>that an A record and a B1 record were inserted. I now want to create an
>instance of B2 that extends from the same A record as B1. Is this possible?
>
>Thanks again.
>
>Matt
>
>[EMAIL PROTECTED] wrote:
>
>>Matt,
>>
>>I believe since the Person and Student object exist it will set there
>>values to null except the personId. Because in the User instance you are
>>storing allthe other fields are null (if you set them to null when you
>>declare them) except the loginName. So, ojb will know that person and
>>student 001 exist and will do and update instead of an insert.
>>
>>You should create them on the first store. Or do not have user extend
>>Student, instead have a 1:1 relationship. Depends on your requirments i
>>guess.
>>
>>-chris worley
>>
>>
>>
>>>I'm trying to figure out how to store a new persisted object that
>>>extends a pre-existing object.
>>>
>>>For example, I have 3 classes: Person, Student, and User. Student and
>>>User extend Person. A Student object already exists, and I now want to
>>>create a User object that inherits from the same Person as the Student
>>>object. Is this possible? Here's a code example:
>>>
>>>User user = new User();
>>>user.setLoginName("matt");
>>>user.setPersonOid("001"); // A pre-existing person
>>>
>>>broker.beginTransaction();
>>>broker.store(user);
>>>broker.commitTransaction();
>>>
>>>The result of the above code is a NEW empty person object being created
>>>with a newly generated OID (via a sequence). How can I associate the
>>>new User with a pre-existing Person?
>>>
>>>Thanks again.
>>>
>>>Matt
>>>
>>>
>>>
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>>>
>>
>>
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