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
