Golang开发之字符串与切片问题踩坑记录

CREATE TABLE `label` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT COMMENT 'id',
  `name` varchar(190) COLLATE utf8mb4_unicode_ci DEFAULT 'label name',
  PRIMARY KEY (`id`),
  UNIQUE KEY `uniq_n` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=7050965 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci COMMENT='label'

const (
   // 最大字符长度
   LabelNameLengthLimit = 190
)
func GetOrCreateLabel(ctx context.Context, name string) (label dao.Label, err error) {
   var err error
   // 依据name查询label信息
   label, err = db_reader.GetLabel(name)
   // 没有找到对应的label信息，且字符串长度超过190，则切片后再次查询
   if IsRecordNotFoundError(err) && len(name) > LabelNameLengthLimit {
      label, err = db_reader.GetLabel(name[:LabelNameLengthLimit])
   }
   // 还是报错，则尝试创建label信息
   if err != nil {
      label.Name = name
      err = db_writer.CreateLabel(ctx, &label)
      // 报唯一键冲突错误，可能是由于并发创建导致的问题，再次兜底进行查询
      if IsKeyConflict(err) {
         label, err = db_reader.GetLabel(ctx, name)
         if err != nil {
            return label, err
         }
      }
      if err != nil {
         return label, err
      }
   }
   return label, nil
}

labelName := "© 2015 Charanga Sí o Ké - Chema Muñoz, Perfecto Artola, Pablo Guerrero, Antonio Flores, Los Gipsy King, Chambao, Adele, La Pegatina, El Chaval de la Peca, Los Manolos © 2015 Charanga Sí o Ké - Sones de Rumba"

var err error
// 依据name查询label信息
label, err = db_reader.GetLabel(name)
// 没有找到对应的label信息，且字符串长度超过190，则切片后再次查询
if IsRecordNotFoundError(err) && len(name) > LabelNameLengthLimit {
   label, err = db_reader.GetLabel(name[:LabelNameLengthLimit])
}

err = db_writer.CreateLabel(ctx, &label)
// 报唯一键冲突错误，可能是由于并发创建导致的问题，再次兜底进行查询
if IsKeyConflict(err) {
   label, err = db_reader.GetLabel(ctx, name)
   if err != nil {
      return label, err
   }
}

// StringHeader is the runtime representation of a string.
// It cannot be used safely or portably and its representation may
// change in a later release.
// Moreover, the Data field is not sufficient to guarantee the data
// it references will not be garbage collected, so programs must keep
// a separate, correctly typed pointer to the underlying data.
type StringHeader struct {
   Data uintptr
   Len  int
}

labelName := "© 2015 Charanga Sí o Ké - Chema Muñoz, Perfecto Artola, Pablo Guerrero, Antonio Flores, Los Gipsy King, Chambao, Adele, La Pegatina, El Chaval de la Peca, Los Manolos © 2015 Charanga Sí o Ké - Sones de Rumba"
fmt.Println("原字符串内容：", labelName)
fmt.Println("字节长度：", len(labelName))
fmt.Println("按照字节截取内容：", labelName[:LabelNameLengthLimit])
fmt.Println("字符长度：", len([]rune(labelName)))
fmt.Println("按照字符截取内容：", string([]rune(labelName)[:LabelNameLengthLimit]))

const (
   // 最大字符长度
   LabelNameLengthLimit = 190
)
func GetOrCreateLabel(ctx context.Context, name string) (label dao.Label, err error) {
   if rs := []rune(name); len(rs) > LabelNameLengthLimit {
      name = string(rs[:LabelNameLengthLimit])
   }
   var err error
   // 依据name查询label信息
   label, err = db_reader.GetLabel(name)
   // 还是报错，则尝试创建label信息
   if err != nil {
      label.Name = name
      err = db_writer.CreateLabel(ctx, &label)
      // 报唯一键冲突错误，可能是由于并发创建导致的问题，再次兜底进行查询
      if IsKeyConflict(err) {
         label, err = db_reader.GetLabel(ctx, name)
         if err != nil {
            return label, err
         }
      }
      if err != nil {
         return label, err
      }
   }
   return label, nil
}