Rails (ActiveRecord) base union

friendship.rb

class Friendship < ActiveRecord::Base

  scope :of_user, ->(user) { union(where(user1_id: user), where(user2_id: user)) }

  class << self
    def union(*relations)
      union_clause = "(#{relations.map {|r| r.ast.to_sql }.join(') UNION (')})"
      as_clause = "AS #{self.table_name}"
    
      from "(#{union_clause}) #{as_clause}"
    end
  end

end