What you're really doing here is creating a multiply inherited class
on the SQL side, which is a use case SQLA was not at all designed to
handle. So the fact that RatableRecord inherits from Soup here is
not ideal since its really a (Ratable, Record). The specific concept
we have no test coverage or support for is that a row in ratings and a
row in records, both subclasses of soup, might share the same primary
key. Additionally, SQLA when constructing the join() for joined
table inheritance assumes the joinable units can be strung together
like plain tables (all the test coverage involves plain tables as
targets), so here we have to bypass that functionality altogether.
It can work for the purposes of this example by forcing a particular
select() statement from the mapping:
orm.mapper(RatableRecord, ratable_record,
with_polymorphic=([RatableRecord],
ratable_record.join(soup,
records.c.id==soup.c.id).select().apply_labels().alias()),
inherits=Soup, inherit_condition=(records.c.id==soup.c.id))
I can't speak for how far you can go with this (meaning functions
which construct joins like query.join() as well as eager loading may
or may not have further issues), and you lock yourself in to a little
more SELECT nesting than might be strictly necessary at a straight SQL
level. The existence of the RatableRecord class and its mapping
probably makes SQLA's polymorphic loading (i.e., from Soup on upwards)
a non-option here, but might work to some degree if you specified
with_polymorphic() on all mappers to force what it selects from in all
cases.
On Jun 14, 2008, at 6:10 AM, Malthe Borch wrote:
> Michael Bayer wrote:
>> oh. how are you getting it to join from soup-> (album join
>> vinyl) ? "soup" has a relation to "album join vinyl" and you're
>> using query.join() ? it should be creating an aliased subquery for
>> the right side of the join in that case. I thought 0.4 was able to
>> do this; 0.5 definitely can.
>
> Attached is the example script from my previous thread, adapted to
> show
> the present issue.
>
> The setup is basically this:
>
> ratable_record = records.join(
> ratings, onclause=(ratings.c.id==records.c.id))
>
> orm.mapper(RatableRecord, ratable_record,
> inherits=Soup, inherit_condition=(records.c.id==soup.c.id))
>
> \malthe
>
> >
> <example.tar.gz>
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