>
> >[56]:cs.filter(default_recipe__ingredients__ingredient__id=3).filter(default_recipe__ingredients__ingredient__id=1)
>> Out[56]:[]
> This would map to a Query that looks like this "... WHERE id=3 AND
> id=1". that would most certainly return no results.
Unless those ingredients were qbits ;) That's my superposition,
and I'm sticking with it! :)
> If you're trying to do OR, look into the DB API manual for Q
> objects, which are the way to express OR statements.
It looks like this might be what the OP was trying to do, which
could be implemented with something like you describe:
cs.filter(
Q(default_recipe__ingredients__ingredient__id=3) |
Q(default_recipe__ingredients__ingredient__id=1)
)
This would return
[<Cocktail: Bloody Mary>, <Cocktail: Screwdriver>]
Alternatively, if it's a short list of IDs, one could also use
Django's __in modifier, something like
cs.filter(default_recipe__ingredients__ingredient__in=[1,3])
(that might have to be
default_recipe__ingredients__ingredient__id__in=[1,3]
with both "id" and "in" rather than just "in"...YMMV)
Alternatively, the the OP may have been trying to do something
I've struggled to do with my current app: wanting to find all N
with both a related X and Y from the same relation. In the above
example, it would be all Cocktail objects that contain both
ingredient=1 and ingredient=3 which would be seen by a slightly
more detailed set of sample data:
"""
In [54]:cs.filter(default_recipe__ingredients__ingredient__id=1)
Out[54]:[<Cocktail: Bloody Mary>, <Cocktail: Screwdriver>]
In [55]:cs.filter(default_recipe__ingredients__ingredient__id=3)
Out[55]:[<Cocktail: Bloody Mary>, <Cocktail: Tomato Juice>]
"""
And you're looking for Cocktail objects that have both
ingredient#1 and ingredient#3 which is only the Bloody Mary
[editor's aside: they're all pretty vile drinks in my book].
To do this, I've had to resort to extra() calls, something like
######################################
ingredients = [1,3]
ingredient_clause = """EXISTS (
SELECT id
FROM app_cocktail_ingredients
WHERE
cocktail_id = app_cocktail.id
AND ingredient_id = %s
)
"""
for ingredient in ingredients:
cs = cs.extra(where=ingredient_clause,
params=[ingredient])
######################################
(not having your full model or DB schema, you'll likely have to
adjust it for your "default_recipe"/"ingredients" interplay).
This will tack on a SQL EXISTS-clause for each ingredient that
should ensure that the cocktail in question has the given
ingredient, without excluding the possiblity of other ingredients.
Performance shouldn't be too bad, assuming you have a sane number
of cocktails and ingredients. I've had a few issues with
performance using PostgreSQL+EXISTS() when the lookup table had
nearly half a million records in it. I'm working the kinks out
of that today. Switching to an IN query didn't help.
Fortunately, I presume your ingredient list doesn't approach such
absurdities. Yippie :-S
Hope this gives you some ideas to work with.
-tkc
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