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
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