module Bullet::Ext::Object

def bullet_join_potential_composite_primary_key(primary_keys)
  return read_attribute(primary_keys) unless primary_keys.is_a?(Enumerable)
  primary_keys.map { |primary_key| read_attribute primary_key }
              .compact.join(',')
end

def bullet_key
  return "#{self.class}:" if respond_to?(:persisted?) && !persisted?
  @bullet_key ||= "#{self.class}:#{bullet_primary_key_value}"
end

def bullet_primary_key_value
  return if respond_to?(:persisted?) && !persisted?
  @bullet_primary_key_value ||=
    begin
      primary_key = self.class.try(:primary_keys) || self.class.try(:primary_key) || :id
      bullet_join_potential_composite_primary_key(primary_key)
    end
end