About o-r mapping

Question

Hi all,
I have two questions when creating database scheme:
1, kodo use a default FlatInheritanceMapping to mapping class inheritance
hierachy to a RDMS.But this is not always a practic way.In most time we
mapping every leaf class in the hierachy to a separate table ,and do not
create any table for the supperclass but mapping their persistent field to
those leaf class table. In this way,redundant data be created indeed ,but
the whole data model become more mainteneable and reasonable. My question
is ,does kodo support this kind of o-r mapping ? if so, how to config the
metadate file ?
2, When using datastore identity,it's not nesseccary for programmers to
implement object id.But how can i access a object's id creaded by JDO
implemention? for example,my application want to compare tow object for
equality by their id,how do I access the id in my program ?
Thanks
Gentri

Answer 1

Thank you Patrick. I have another question: does kodo support non-durable
identity ?
Gentri
"Patrick Linskey" <[email protected]>
??????:[email protected]..
On Sat, 19 Jul 2003 18:13:41 +0800, Gentri wrote:
Hi all,
I have two questions when creating database scheme:
1, kodo use a default FlatInheritanceMapping to mapping class
inheritance
hierachy to a RDMS.But this is not always a practic way.In most time we
mapping every leaf class in the hierachy to a separate table ,and do not
create any table for the supperclass but mapping their persistent fieldto
those leaf class table. In this way,redundant data be created indeed,but
the whole data model become more mainteneable and reasonable. Myquestion
is ,does kodo support this kind of o-r mapping ? if so, how to configthe
metadate file ?Kodo does not currently support this type of mapping. It's on our radar
screens, and we anticipate supporting it in the next couple months.
2, When using datastore identity,it's not nesseccary for programmers to
implement object id.But how can i access a object's id creaded by JDO
implemention? for example,my application want to compare tow object for
equality by their id,how do I access the id in my program ?You can do:
Object oid1 = JDOHelper.getObjectId (o1);
Object oid2 = JDOHelper.getObjectId (o2);
if (oid1 != null && oid1.equals (oid2))
// do stuff
This works with both application and datastore identity.
Note, however, that the JDO spec guarantees that no matter how you
navigate to an object within a given persistence manager, you will always
obtain the same object reference within that PM, and you will always
obtain different object references within different PMs.
That means that if o1 and o2 were both obtained in the same PM, you can
just do an == comparison to see if they represent the same data.
-Patrick
Patrick Linskey
SolarMetric Inc.