How to return an empty ActiveRecord relation?

Question

If I have a scope with a lambda and it takes an argument, depending on the value of the argument, I might know that there will not be any matches, but I still want to return

Answer 1

Use scoped:

scope :for_users, lambda { |users| users.any? ? where("user_id IN (?)", users.map(&:id).join(',')) : scoped }

But, you can also simplify your code with:

scope :for_users, lambda { |users| where(:user_id => users.map(&:id)) if users.any? }

If you want an empty result, use this (remove the if condition):

scope :for_users, lambda { |users| where(:user_id => users.map(&:id)) }