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From: "Summers, John1 " <john1.summers@citi.com>
To: "'user@cayenne.apache.org'" <user@cayenne.apache.org>
Date: Thu, 1 Apr 2010 16:49:33 +0100
Subject: can Cayenne handle an inheritance model like this?...
Thread-Topic: can Cayenne handle an inheritance model like this?...
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Hello Apache-Cayenne users,

I am engaged on a project where we are trying to replace a messy bespoke Da=
ta Access Layer with a more modern ORM framework. We have been looking at H=
ibernate but it cannot handle our inheritance model. I would like to ask if=
 Cayenne can handle such a model because if it can we will continue and mak=
e a full assessmet of Cayenne. I will describe the model to you now:

Ok the database tables look like this:

BASEENTITY
-ID
-LINKID

TRADE
-ID

INSTR
-ID

And the Java object hierarchy is that BaseEntity is the superclass with Tra=
de and Instr (and others) as the subclass.

Here's the rub...

The ID fields on the 3 tables do NOT express a hierarchy. They are unique t=
o each table only. You cannot look up a Trade's BaseEntity by using the tra=
de ID and finding a matching LINKID in BaseEntity.

The connection is actually the BASEENTITY.LINKID field. The LINKID matches =
IDs in the TRADE or INSTR table. Like this:

BASEENTITY
ID=3D1, LINKID=3D100
ID=3D2, LINKID=3D200

TRADE
ID=3D100

INSTR
ID=3D200

Hibernate cannot handle this. Unidirectional one to one relationships requi=
re annotation on each end. The 'table per class' inheritance model requires=
 the ID fields in TRADE and INSTR to be foreign keys of BASEENTITY, which t=
hey are not.

Look forward to any advice.
Thanks,
John


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