def destroy_keys! attribute, *keys
      raise "invalid attribute #{attribute}" unless self.class.column_names.include?(attribute.to_s)
      destroy_keys(attribute, *keys).save
    end
def destroy_keys! attribute, *keys
      raise "invalid attribute #{attribute}" unless self.class.column_names.include?(attribute.to_s)
      destroy_keys(attribute, *keys).save
    end
Deletes many keys in a record. E.g.
   witt = Person.find_by_name("Ludwig Wittgenstein")
   witt.destroy_keys!(:info, :father, :mother)
 It does save the record.