Rails self referrential associations, how to determine mutual intersection?

Question

I want to have friends/followers mechanzm, so I've created following DB structure:

user_id
friend_id   

I want to know what's the easiest and simplest way to determine (Rails-way) that following users are mutual friends?

user_id        friend_id
1              2
2              1

Answer 1

Try this:

test_pair = [1,2]
Friendship.where(user_id: test_pair, friend_id: test_pair).count == 2