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From Andy Jefferson <a...@jpox.org>
Subject Re: Inheritance proposal
Date Tue, 09 Aug 2005 15:06:23 GMT
> Suppose there are two non-abstract persistence-capable classes A and B.
> Class B extends A. Both explicitly define the inheritance strategy
> new-table. Class A maps to table TA and B maps to table TB. Then there
> are still two scenarios possible, depending on where to store the
> inherited fields of B instances:
> (1) In table TA. Then we need a <join> element, since a class B instance
> is represented by a row in table TA and a row in table TB.
> (2) In table TB. No <join> element is needed since TB includes columns
> for the inherited fields. So TA only has rows for class A instances, not
> for B instances.

Hi Michael,

that's not our interpretation of the spec :-)

In your example if both classes have "new-table" then we have the fields 
specified in class A persisted into table TA, and the fields specified in 
class B persisted into table TB - so option 1 (ONLY), and we do not need any 
<join> unless wanting to override the join column names (pk columns). An 
instance of B will have a row in TA, and an associated row in TB. An instance 
of A will have a row in TA only.

The only difference we see from option 1 is where the user decides to override 
the <field> specifications for a field of A, in class B
e.g 
<class name="B">
    <field name="A.field1"/>
</class>
which would mean that table TB will carry the value for that field (rather 
than the column in table TA).




-- 
Andy
Java Persistent Objects - JPOX

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