douzai1074 2014-06-21 20:30
浏览 72
已采纳

带有temptemp的元帅sql.NullString

How is one supposed to not render the null sql.NullString if it is not valid? - http://play.golang.org/p/pzSWS9vE0J

It doesn't seem to be working with omitempty struct tag and I can't quite figure out what to return from the MarshalJSON such that omitempty will be honored

type NS struct {
    sql.NullString
}

func (ns *NS) MarshalJSON() ([]byte, error) {
    fmt.Println("Marshaling json for NS")
    if ns.String == "" && !ns.Valid {
        return []byte("null"), nil
    }
    return json.Marshal(ns.String)
}

type A struct {
   RStr string `json:rstr,omitempty"`
   Str NS `json:"str,omitempty"`
}


func main() {
    a := A{RStr: "rstr"}
    s, _ := json.Marshal(&a)
    fmt.Println(string(s))
}
  • 写回答

1条回答 默认 最新

  • dongying2112 2014-06-22 00:16
    关注

    As far as I know, there's no way to do that, however you can always use a pointer instead : http://play.golang.org/p/b4Q7YgpUa-

    func main() {
        a := A{"rstr", &sql.NullString{"Test", true}}
        s, err := json.Marshal(&a)
        fmt.Println(string(s), err)
        a = A{}
        fmt.Println(json.Unmarshal(s, &a))
        fmt.Printf("%v %v
    ", a.RStr, a.Str.String)
        a = A{RStr: "rstr"}
        s, err = json.Marshal(&a)
        fmt.Println(string(s), err)
    }
    

    The reason why a pointer makes a difference from http://tip.golang.org/pkg/encoding/json/#Marshal:

    -the field is empty and its tag specifies the "omitempty" option.

    The empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

报告相同问题?

悬赏问题

  • ¥15 使用ESP8266连接阿里云出现问题
  • ¥15 被蓝屏搞吐了,有偿求帮解答,Ai回复直接拉黑
  • ¥15 BP神经网络控制倒立摆
  • ¥20 要这个数学建模编程的代码 并且能完整允许出来结果 完整的过程和数据的结果
  • ¥15 html5+css和javascript有人可以帮吗?图片要怎么插入代码里面啊
  • ¥30 Unity接入微信SDK 无法开启摄像头
  • ¥20 有偿 写代码 要用特定的软件anaconda 里的jvpyter 用python3写
  • ¥20 cad图纸,chx-3六轴码垛机器人
  • ¥15 移动摄像头专网需要解vlan
  • ¥20 access多表提取相同字段数据并合并