# File lib/dm-validations/uniqueness_validator.rb, line 17
      def call(target)
        scope = Array(@options[:scope])

        return true if @options[:allow_nil] && target.send(field_name).nil?

        repository_name = target.repository.name

        opts = {
          :fields    => target.model.key,
          field_name => target.validation_property_value(field_name)
        }

        scope.each do |item|
          if target.model.properties(repository_name).has_property?(item)
            opts[item] = target.validation_property_value(item)
          elsif target.model.relationships(repository_name).has_key?(item)
            target.validation_association_keys(item).each do |key|
              opts[key] = target.validation_property_value(key)
            end
          end
        end

        resource = repository(repository_name) { target.model.first(opts) }

        return true if resource.nil?

        # is target and found resource identic? same instance... but not ==
        return true if !target.new_record? && resource.repository.name == repository_name && resource.model == target.model && resource.key == target.key

        error_message = @options[:message] || ValidationErrors.default_error_message(:taken, field_name)
        add_error(target, error_message, field_name)

        return false
      end