can't dump anonymous class #<Module -error on caching in rails 3

Question

I am getting can't dump anonymous class error.

I have the following methods in my model.

 def seating_for(active)
   ln = cache(col("lu", active)) do
    self.seat_list_for(active).where(seat_id: self.seat_entries)
 end

 def seat_list_for(active)
   ex_id = Exc.id_by_symbol(active)
   self.row.exe.seats.where(ex_id: exc_id).first.seat_alloc_mem
 end

I am trying to cache ln. I am getting an error. Can't figure out what is the problem.

 can't dump anonymous class #<Module:0x00000007ab6088>
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/activesupport-3.2.14/lib/active_support/cache.rb:561:in `dump'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/activesupport-3.2.14/lib/active_support/cache.rb:561:in `initialize'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/redis-activesupport-3.2.4/lib/active_support/cache/redis_store.rb:34:in `new'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/redis-activesupport-3.2.4/lib/active_support/cache/redis_store.rb:34:in `block in write'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/activesupport-3.2.14/lib/active_support/cache.rb:520:in `instrument'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/redis-activesupport-3.2.4/lib/active_support/cache/redis_store.rb:33:in `write'
 /home/#/.rvm/gems/ruby-2.0.0-p0@anon-ui/gems/activesupport-3.2.14/lib/active_support/cache.rb:299:in `fetch'
 /home/#/user/projects/app/#/lib/lib_utility.rb:15:in `cache'
 /home/#/user/projects/app/#/app/models/smthng.rb:566:in `seating_for'

lib/lib_utility.rb

module LibUtility
  module ClassMethods
    def col(p, l)
     //smthng
    end

   def cache(l, options={}, &b)
     Rails.cache.fetch(l, expires_in: 50.minutes, &b)
   end
  end

  def self.included(receiver)
    receiver.extend ClassMethods
  end

end

Needs guidance??

Answer 1

The problem is that you try to cache an ActiveRecord relation collection. That is not possible. If you want to cache the query, you need to make it an array first

def seating_for(active)
  cache(col("lu", active)) do
    self.seat_list_for(active).where(seat_id: self.seat_entries).to_a
  end
end