preload_has_one_association

# File activerecord/lib/active_record/association_preload.rb, line 112
      def preload_has_one_association(records, reflection, preload_options={})
        id_to_record_map, ids = construct_id_map(records)        
        options = reflection.options
        if options[:through]
          records.each {|record| record.send(reflection.name) && record.send(reflection.name).loaded}
          through_records = preload_through_records(records, reflection, options[:through])
          through_reflection = reflections[options[:through]]
          through_primary_key = through_reflection.primary_key_name
          unless through_records.empty?
            source = reflection.source_reflection.name
            through_records.first.class.preload_associations(through_records, source)
            through_records.each do |through_record|
              add_preloaded_record_to_collection(id_to_record_map[through_record[through_primary_key].to_s],
                                                 reflection.name, through_record.send(source))
            end
          end
        else
          records.each {|record| record.send("set_#{reflection.name}_target", nil)}

          set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options), reflection.primary_key_name)
        end
      end