On 17 December 2010 19:20, Jonas H. <jo...@lophus.org> wrote:
> Hello!
>
> Assuming the following data model:
>
> +------+ +------+ +-----+
> | Blog | has many (1:n) | Post | tagged with (n:m) | Tag |
> +------+ +------+ +-----+
>
> I want to filter out all blogs that have a post tagged with "foo" and "bar"
> (the same post satisfying *both* conditions).
>
> How would that query look like? Intuitively I'd say
>
> Blog.objects.filter(post__tags__name="foo",
> post__tags__name="bar")
>
> but obviously that's a SyntaxError because of the repeated keyword argument
> to filter(). I also tried Q() objects but that generates some totally
> unrelated queries.
In [9]: print Blog.objects.filter(Q(post__tags__name="foo") &
Q(post__tags__name="bar")).query
SELECT "simple_blog"."id"
FROM "simple_blog"
INNER JOIN "simple_post" ON ("simple_blog"."id" =
"simple_post"."blog_id")
INNER JOIN "simple_post_tags" ON ("simple_post"."id" =
"simple_post_tags"."post_id")
INNER JOIN "simple_tag" ON ("simple_post_tags"."tag_id" =
"simple_tag"."id")
WHERE ("simple_tag"."name" = foo AND "simple_tag"."name" = bar )
Looks related. It's exactly what you specified, but conditions you
gave are just impossible to satisfy.
Your task is a bit more complicated to do in SQL:
Blog.objects.filter(post_tags__name__in=["foo",
"bar"]).annotate(match_count=Count('post__tags')).filter(match_count=2)
This should give you the right results.
--
Łukasz Rekucki
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