Persisting inner classes with inheritance

mitchellch · **Joined:** Wed Sep 03, 2003 9:56 pm **Posts:** 58

I'm implementing the 'State' pattern from the 'Applied Java Patterns' book, and would like to be able to persist the current state using Hibernate. I've run into troubles because the State pattern dictates that the state classes (one per state) be inner classes of the context object. My context object is also persistant.

To simplify, given class A (the context), with inner state classes A.a, A.b and A.c, is it possible to map all four classes to two tables (A.a, A.b an A.c all inherit from A.z)

The inner classes (A.a, A.b and A.c) all extend base class A.z (also inner), and must map to the same table. Object 'A' maps to table TABLE_A and objects A.z, A.a, A.b and A.c all map to TABLE_B. I've been attempting 'table per class hierarchy' (unsuccessfully).

I'm able to get this working if I make the state classes separate/standalone, but not if I put them inside the context object ('A'). The problem with this approach is that the (3) state classes need to access the context object's instance data.

I know this is a rather complex scenario, but I don't seem to have trouble with the simple ones. ;)

-Mitch

michael · **Posted:** Tue Dec 30, 2003 4:57 pm

Hope the right tread this time ...

Just an idea, have you tried using the $ syntax in your mapping documents, like de.blabla.A$B where B is your inner class, and A your outer? This may work, but maybe just for static inner classes, I don't think for normal inner classes.

I don't really think Hibernate can persist normal inner classes, on retrieval, the link to the parent would have to be created somehow, and I don't think this is possible ... but maybe Hibernate surprises me once more ;) Does someone else know something about this?

max · **Posted:** Tue Dec 30, 2003 5:26 pm

It is not supported - and cannot be done (AFAIK).

you can save *static* inner classes - but then you won't get that part saved.

How about remodelling it as classes with a has-a reference to the Context ? Should be just as good!

mitchellch · **Joined:** Wed Sep 03, 2003 9:56 pm **Posts:** 58

The 'has-a' approach is what I'm currently working on. This should work fine, however there is one point on which I'm still confused.

The Chapter 16 of the Reference Doc states the following...

"Suppose we have an *interface* Payment..."

and proposes the following mapping

Code:

<class name="Payment" table="PAYMENT_ID">
    <id/>
    <discriminator column="PAYMENT_TYPE" type="string"/>
    <property name="amount column="AMOUNT"/>
    <subclass name="CreditCardPayment" discriminator-value="CREDIT"/>
    <subclass name="CashPayment" discriminator-value="CASH"/>
    <subclass name="ChequePayment" discriminator-value="CHEQUE"/>
</class>

Is this accurate? Can I specify an *Interface* as persistent? If so, what would my Configure.addClass() calls look like?

I just cannot get this to work.

michael · **Posted:** Tue Dec 30, 2003 6:01 pm

config.addClass(Payment.class)? Alternatively use config.addFile()

mitchellch · **Joined:** Wed Sep 03, 2003 9:56 pm **Posts:** 58

Ridiculous type. Sorry. The Configure.addClass("Payment") works fine. Sorry.

mitchellch · **Joined:** Wed Sep 03, 2003 9:56 pm **Posts:** 58

"Ridiculous type" should be "Ridiculous typo"...sorry.