# File lib/mongoid/relations/builders/nested_attributes/one.rb, line 24
          def build(parent)
            return if reject?(parent, attributes)
            @existing = parent.send(metadata.name)
            if update?
              existing.attributes = attributes
            elsif replace?
              parent.send(metadata.setter, Mongoid::Factory.build(metadata.klass, attributes))
            elsif delete?
              parent.send(metadata.setter, nil)
            end
          end