On Thu, 2007-10-04 at 20:08 +0000, bill wrote:
> Hi folks,
> I've reviewed the db api documentation page, and I'm pretty sure it
> didn't have an example that would help me with this request. I'd like
> something like the "IN" operator that can be used in a lookup on a
> field in a related model, but more like something that I guess could
> be called something like "ALL_IN". Example:
> Models:
> Article (title, pub_date, etc...)
> TaggedArticle (article_id, tag)
>
> One article can of course have multiple tags. What if I wanted to
> find Articles that have _all_ the tags in a particular set. Similar
> to IN:
>
> Article.objects.filter(taggedarticle__tag__in=['python', 'perl',
> 'java'])
>
> That would give me articles that have tags for python OR perl OR
> java. But what if I want a quick way to find all articles that have
> all three of those tags (they may have more tags, but they at least
> have all of those three.)
>
> I've learned about making my own Manager class, so that's definitely
> possible, but does there happen to be a built-in way?
At the moment, this isn't possible. You can use the method in [1] to do
it right now, though. In the near future, once the queryset refactor is
finished, you'll be able to do this as
A.
Article.objects.filter(tag='python').filter(tag='perl').filter(tag='java')
or something like (I've possibly screwed up the syntax, but you get the
idea):
Article.objects.filter(Q(tag='python'), Q(tag='perl'), Q(tag='java'))
because many-to-many filters will successively restrict the result set.
However, that doesn't work right now because we don't do the correct
self-joins to form the right SQL. [By the way, it will also be possible
to construct this
[1] http://www.pointy-stick.com/blog/2006/06/14/custom-sql-django/
Regards,
Malcolm
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