On Friday 11 January 2008 17:03:06 Alexandre Conrad wrote:
> svilen wrote:
> > On Friday 11 January 2008 16:12:08 Alexandre Conrad wrote:
> >>Channel -> Playlist -> Media
> >>Channel -> CatalogChannel(Catalog) -> Media
> >>
> >>(Media has a fk to Catalog, not CatalogChannel)
> >>The only element I have, is "playlist" (instance of Playlist). At
> >>this point, I need to find out the available Media of the
> >>Playlist's Channel's catalog so I can attach them to the
> >> Playlist.
> >>
> >>At first, I tryied out:
> >>
> >>Media.query.join(["catalog",
> >>"channel"]).filter(Channel.c.id==playlist.id_channel).all()
> >>
> >>But then it complains that "channel" is not part of the Catalog
> >>mapper. Catalog ? I want it to be looking at CatalogChannel, this
> >>is the one having the "channel" relation, not Catalog.
> >
> > i see what u want, but formally (computer languages are formal,
> > SA is a language) u are contradicting yourself. u said above that
> > media points to catalog and not to catalogchannel. How u expect
> > it to find a .channel there?
>
> I was expecting that SA would know that from the polymorphic "type"
> flag. I have a "catalog" relation on media. When I do
> media.catalog, it doesn't just return a Catalog object, but really
> a CatalogChannel object
hey, polymorphic means ANY subtype, u could have 5 other CatalogRivers
that have no .channel in them... how to guess which one? Find the one
that has .channel? the root-most one or some of its children-klasses?
> (which is the whole point of polymorphic
> inheritance). And I thought it could figure out channel from that.
> But Mike said no. :) That's why he talked about having some extra
> API query methods:
>
> Media.query.join_to_subclass(CatalogChannel).join("channel").filter
>(Channel.c.id==playlist.id_channel).all()
>
> We could even join classes only directly (isn't this ORM after
> all?):
>
> Media.query.join([CatalogChannel, Channel])
this is completely different beast. it might be useful... although the
whole idea of the join(list) is list of attribute-names and not
klasses/tables - to have a.b.c.d.e.f, i.e. be specific and avoid
thinking in diagram ways (klasA referencing klasB means nothing if it
happens via 5 diff.attributes)
when i needed similar thing, a) i moved the .channel into the root or
b) changed media to reference CatChannel and not the base one.
ciao
svilen
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