How to join on the same table multiple times?

Question

I\'m querying for the mutual friends of a given two users. The query below should do the trick for the most part and the friendship table should be self-evident, containing

Answer 1

I do it with string arguments to joins:

User.
  joins("INNER JOIN friendships a ON users.id = a.friend_id").
  joins("INNER JOIN friendships b ON users.id = b.friend_id").
  where("a.user_id" => 1, "b.user_id" => 2)

I'm not aware of a higher-level way to do such a join with Active Record.

Answer 2

Firstly, you should have proper Model Relationship between User & Friendship.

user model:
 has_many :friendships

friendship model:
 belongs_to :user

with that: you can get activerecords in your iteration like:

users = User.all
users.each do |user|
 user.friendships
 .....
end

Or, by specific user, like:

user = User.first
user.friendships #returns association

or 

User.first.friendships

for 2 specific users (given), you can do like:

User.where(id: [1,2]) #array of user id, then get the friendship record as above.

Hope this helps!