count

# File activerecord/lib/active_record/associations/collection_association.rb, line 251
      def count(column_name = nil)
        relation = scope
        if association_scope.distinct_value
          # This is needed because 'SELECT count(DISTINCT *)..' is not valid SQL.
          column_name ||= reflection.klass.primary_key
          relation = relation.distinct
        end

        value = relation.count(column_name)

        limit  = options[:limit]
        offset = options[:offset]

        if limit || offset
          [ [value - offset.to_i, 0].max, limit.to_i ].min
        else
          value
        end
      end