class RSolr::Xml::Generator

def to_xml(doc)
  lambda do |doc_node|
    doc.fields.each do |field_obj|
      value = field_obj.value
      if field_obj.name.to_s == RSolr::Document::CHILD_DOCUMENT_KEY
        child_node_builder = to_xml(field_obj.value)
        self.class.use_nokogiri ? doc_node.doc_(&child_node_builder) : doc_node.doc(&child_node_builder)
      elsif value.is_a?(Hash) && value.length == 1 && field_obj.attrs[:update].nil?
        update_attr, real_value = value.first
        doc_node.field real_value, field_obj.attrs.merge(update: update_attr)
      elsif value.nil?
        doc_node.field field_obj.value, field_obj.attrs.merge(null: true)
      else
        doc_node.field field_obj.value, field_obj.attrs
      end
    end
  end
end