validate_each

# File activerecord/lib/active_record/validations/uniqueness.rb, line 19
      def validate_each(record, attribute, value)
        finder_class = find_finder_class_for(record)
        value = map_enum_attribute(finder_class, attribute, value)

        relation = build_relation(finder_class, attribute, value)
        if record.persisted?
          if finder_class.primary_key
            relation = relation.where.not(finder_class.primary_key => record.id_in_database)
          else
            raise UnknownPrimaryKey.new(finder_class, "Can not validate uniqueness for persisted record without primary key.")
          end
        end
        relation = scope_relation(record, relation)
        relation = relation.merge(options[:conditions]) if options[:conditions]

        if relation.exists?
          error_options = options.except(:case_sensitive, :scope, :conditions)
          error_options[:value] = value

          record.errors.add(attribute, :taken, error_options)
        end
      end