On Aug 5, 2008, at 9:35 AM, Marcin Skladaniec wrote:
I think you are talking about VERTICAL inheritance, not horizontal
here. In case of horizontal you wouldn't have a relationship
between subclass/superclass tables. Anyways, assuming we are
discussing vertical inheritance, yes, there is a relationship
involved. Per JPA approach, this relationship can be figured
automatically : it is a 1..1 relationship between the PK's of two
tables. So we don't have to store it in XML, as we can find it in
runtime. Still internally there should be a concept of a
relationship joining parent and child tables, so you are right
about the big picture.
I'm now confused with vertical-horizontal naming. You say vertical,
jira https://issues.apache.org/cayenne/browse/CAY-795says
horizontal. I guess we talk about the same thing anyway, but just to
be sure: I'm trying to model a database schema where there are 3
tables: Artwork, Painting and Sculpture.
Artwork is an abstract entity with its own table
Painting and Sculpture are extending Artwork, but have their own
tables as well.
You are suggesting that both superclass and subclass should have PK,
this means yet another table in required to link the two tables.
This seems odd to me as the relationship is simple 1..1, is that a
requirement of JPA ?
I'm reading up on JPA, but I cannot find it.
I guess CAY-795 is just not specific enough. It says "horizontal" in
the title, but the steps to implement it are described in a rather
generic fashion. Not sure if we have a separate Jira for vertical?
Maybe Ari can open a new Jira on that.
Thanks,
Andrus
