> The two arrays are just normal dictionaries that look something like
> this:
>
> friends = [id=1,id=2,id=3]
> friends2 = [id=3]
This is the first suspicious item because if it is a dictionary,
the key "id" appears more than once -- something that can't
happen with a dict.
Sets are the usual tool for this, and until friend relationships
exceed tens-of-thousands (where the number of IDs makes for an
unwieldy query or list stashed in memory), should be usable:
me = Person.objects.get(my_id)
my_friends = me.friend_set
my_friends_ids = set(friend.id
for friend
in my_friends)
other_person = Person.objects.get(other_id)
their_friends = other_person.friend_set
their_friend_ids = set(friend.id
for friend
in their_friends)
# your magic happens here:
common_friend_ids = my_friends_ids.intersection(
their_friend_ids)
# if you want more than their IDs, you have to ask for them
common_friends = Person.objects.in_bulk(
tuple(common_friend_ids))
(that in_bulk() call doesn't seem to like using a set() for its
source of IDs, only allowing list/tuple rather than arbitrary
iterables)
It might also be possible to do this via the extra() call to add
your own funky sifting on the DB side. This could end up being
considerably faster -- but I'd have to think longer about how to
do that one, so I'll leave it as an exercise to the reader. ;-)
-tim
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