represent inheriting mappers PK's based on root tables PK only / root class for identity_key

[Mike Bayer]

i.e. the bottom point of a joined table inheritance chain.

[Mike Bayer]

this is in changeset:3025.

it hasnt been implemented for concrete inheritance. what concrete needs in this area is a requirement that primary keys be distinct across the collection of all concrete mappers; this can be achieved by adding the "polymorphic_on" column to its primary key columns. However, then all query.get() methods need to take on a two-scalar argument signature, which is also a surprise since querying from the subclasses mapper should not need the second PK argument, which then implies some kind of intelligence would need to be added to get() in order to pull this off.

[Mike Bayer]

Removing milestone: 0.4.0 (automated comment)