Hi Lachlan,
thanks for the feedback. I think I'll be moving ahead with this design
(and I wish I had more time for Cayenne work in general)...
Andrus
On Jun 2, 2010, at 10:43 PM, Lachlan Deck wrote:
On 01/06/2010, at 11:38 PM, Andrus Adamchik wrote:
On May 31, 2010, at 9:11 AM, Andrus Adamchik wrote:
BTW, semantically "vertical inheritance with discriminator" is
essentially single-table inheritance with flattened attributes in
subclasses. Which Cayenne supports already, but without any
special optimizations for wide|deep hierarchies.
Pounding on this idea some more ... Since we can't get away from
using entity qualifier (discriminator) at least in some cases for
performance reasons, and I hate to add multiple strategies, maybe
we do make the qualifier required and treat vertical as a special
case of single table with subclasses mapped to the same root table,
and having flattened attributes mapped to subclass-specific table.
The benefits of that are:
* No implicit inheritance relationship from super to sub table. It
is explicitly mapped inside flattened attributes.
* More intuitive mapping, easier to visualize attributes, as all
attributes are rooted in the same base table.
* Can potentially handle more than one joined table per subclass,
or the same join table for multiple subclasses, or a mix of single
table mapping with joined table mapping. I.e. in the spirit of
Cayenne, we'd allow users to follow a generic DB semantics in their
mapping instead of forcing an arbitrary ORM concepts on a (legacy)
DB schema.
* No new concepts for the backend or Modeler to deal with.
+1
Now we still need to do some work with this design:
* Make sure SELECT/INSERT/DELETE/UPDATE work correctly with
flattened attributes over 1..1 relationships, and especially when
inheritance is involved.
* Add convenience Modeler methods to flatten all attributes at once
for a given relationship to simplify subclass mapping.
* Add performance optimizations per Mike's idea, limiting the
number of joins done in a single query.
Mike, do you see any holes in this design?
Looks good.
with regards,
--
Lachlan Deck
