def aggregate(function, format = {:format => nil})
raise(DDLValidationError, "Formats supplied to aggregation functions should be a hash") unless format.is_a?(Hash)
raise(DDLValidationError, "Formats supplied to aggregation functions must have a :format key") unless format.keys.include?(:format)
raise(DDLValidationError, "Functions supplied to aggregate should be a hash") unless function.is_a?(Hash)
unless (function.keys.include?(:args)) && function[:args]
raise DDLValidationError, "aggregate method for action '%s' missing a function parameter" % entities[@current_entity][:action]
end
entities[@current_entity][:aggregate] ||= []
entities[@current_entity][:aggregate] << (format[:format].nil? ? function : function.merge(format))
end