Limit number of objects in has_many association

Question

I have an album which has_many photos. A counter_cache setup updates the photos_count column in the album table. How do I limit the number of photos for an album?

Answer 1

ActiveRecord::Base.transaction do
  ActiveRecord::Base.connection.execute('LOCK TABLE pictures IN EXCLUSIVE MODE')
  if (@album.pictures.count < 10) 
    @album.pictures.create()
  end
end

I believe this is the most correct solution. It guards against concurrency issues/race conditions.