# File lib/mongoid/validations/uniqueness.rb, line 43
      def validate_each(document, attribute, value)
        if document.embedded?
          return if skip_validation?(document)
          relation = document._parent.send(document.metadata.name)
          criteria = relation.where(criterion(document, attribute, value))
        else
          criteria = klass.where(criterion(document, attribute, value))
        end
        criteria = scope(criteria, document, attribute)
        document.errors.add(attribute, :taken) if criteria.exists?
      end