Drew,
I'd only be speculating if I formed a response to this question, as
I've never attempted what you're trying.
Have you actually given a go at this? What implementation are you
using?
- Chris Beams
On Oct 25, 2007, at 7:31 PM, Drew Lethbridge wrote:
Greetings,
I have a question about JDO2.0. When using an inheritance strategy
of "superclass-table", is it valid for two separate subclasses
which both have an identically-typed field to actually share a
database column, rather than specifying a separate column for each
of the fields? As far as I can tell, the JDO spec is not clear on
this. Is it completely JDO-vendor implementation dependent (i.e.
non-portable)?
Below is an illustrative example. B extends A and also C extends
A. The fields B.f1 and C.f2 are both declared as references to a
persistence type "F" but defined to share the column named
F_JDOID. Any potential problems with this?
Thanks.
Drew.
<class name="A" table="A">
<!-- abstract superclass -->
<datastore-identity column="JDOID" />
<inheritance>
<discriminator strategy="value-map" column="CLASSIND" />
</inhertance>
<version strategy="version-number" column="JDOVERSION" />
</class>
<class name="B">
<!-- extends A -->
<inheritance strategy="superclass-table" />
<discriminator value="B" />
</inheritance>
<field name="f1" column="F_JDOID">
<foreign-key deferred="true" />
</field>
</class>
<class name="C">
<!-- extends A -->
<inheritance strategy="superclass-table">
<discriminator value="C" />
</inheritance>
<field name="f2" column="F_JDOID">
<foreign-key deferred="true" />
</field>
</class>
<class name="F" table="F">
<datastore-identity column="JDOID" />
<!-- etc... -->
