def trend_for(klass)
      unless klass.constantize.ancestors.include?Cequel::Record
        raise ArgumentError, "Class #{ klass } does not represent a DB Model"
      else
        @trend_for = klass
      end
    end
def trend_for(klass)
      unless klass.constantize.ancestors.include?Cequel::Record
        raise ArgumentError, "Class #{ klass } does not represent a DB Model"
      else
        @trend_for = klass
      end
    end
Define the class for which trends shall be found