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
(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])
> your query above is missing the isinstance-filter specifying that u
> need catalogchannels and not just any catalogs. i'm not sure how this
> would be expressed in SA but it has to be explicit - and probably
> somewhere on level of tables.
> have u tried
> Media.query.join( ["catalog", "id", "channel"])... ???
Nope, that doesn't work, it's like doing (["catalog", "catalog", "channel"])
Regards,
--
Alexandre CONRAD
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