gistfile1.rb

   # yield chunks (Array) of the full query to a block
   # generates new Collections via self.model.all
   # which has the advantage of dropping scope on
   # hydrated objects
   def block_batches(chunksize, &block)
       new_options = self.query.options.dup
       total = new_options[:limit] || self.count

       new_options[:limit] = chunksize
       new_options[:offset] = 0        
       (total / chunksize.to_f).ceil.times do |page|
           yield self.model.all(new_options)
           new_options[:offset] += chunksize
           new_options[:limit] = [chunksize, total - new_options[:offset]].min
       end
    end