count (DataMapper::AggregateFunctions)

    # File lib/dm-aggregates/aggregate_functions.rb, line 29
        def count(*args)
          query         = args.last.kind_of?(Hash) ? args.pop : {}
          property_name = args.first

          if property_name
            assert_kind_of 'property', property_by_name(property_name), Property
          end

          aggregate(query.merge(:fields => [ property_name ? property_name.count : :all.count ]))
        end