Polymorphic “Visible To” Scope with Arel

                  class Collection < ApplicationRecord
  has_many :memberships

  def self.visible_to(member)
    collections = arel_table
    memberships = Membership.arel_table

    join = collections.join(memberships).on(memberships[:collection_id].eq(collections[:id])).join_sources

    joins(join)
      .where(memberships[:member_id].eq(member.id))
      .where(collections[:archived_at].eq(nil))
      .distinct
  end
end