Question

SQL:

select * from user where room_id not in (select id from rooms);

what is the same equivalent query in rails console with this sql?

ex:

User.all.each { |u| user.room }

(sorry, but this example is not correct.)

Answer 1

User.where("room_id not in (select id from rooms)")

but you want this since it would be rather faster:

User.where("not exist (select id from rooms where id=users.room_id)")

that’s the closest you can get. There appears to be no way to create an Active Record query that translates to SQL NOT(). A search on the subject returns a bunch of SO questions with much the same answer.

You could do something like

User.all.select { |u| !Room.find_by_id(u.room_id) }

But that could be less efficient again.