在运行时覆盖Go JSON标签值

huangapple
go评论193阅读模式
英文:

Override Go JSON tag values at runtime

问题

我在我的Web应用程序中使用"encoding/json"有以下的结构体：

  1. type CourseAssignment struct {
  2.     Semester int `json:"semester" xml:"semester"`
  3.     Lecture Lecture `json:"-" xml:"-"`
  4.     Cos Cos `json:"-" xml:"-"`
  5.     Links map[string][]Link `json:"links,omitempty" xml:"links,omitempty"`
  6. }

Lecture和Cos本身是复杂的结构体，我不希望它们被包含在我的序列化JSON中，所以我通过设置json:"-"来指示。

这个方法完美地运行。

在运行时，我如何在需要的时候覆盖这种行为，而不编写自己的序列化代码？

我的解决方案如下：

  1. func (r *CourseAssignment) Expand(depth int) CourseAssignment {
  2.     if depth <= 0 {
  3.         return *r
  4.     }
  6.     tmp := *r
  7.     tmp.LectureEx = tmp.Lecture
  8.     tmp.CosEx = tmp.Cos
  9.     tmp.Links = nil
  10.     return tmp
  11. }
  13. type CourseAssignment struct {
  14.     Semester int `json:"semester" xml:"semester"`
  15.     Lecture *Lecture `json:"-" xml:"-"`
  16.     Cos *Cos `json:"-" xml:"-"`
  17.     Links map[string][]Link `json:"links,omitempty" xml:"links,omitempty"`
  18.     LectureEx *Lecture `json:"lecture,omitempty" xml:"lecture,omitempty"`
  19.     CosEx *Cos `json:"course_of_study,omitempty" xml:"course_of_study,omitempty"`
  20. }

当我想要包含这些字段时，我使用Expand创建对象的副本，该副本填充了包含相同引用但在序列化中显示的字段。

英文:

I have the following struct in in my Web Application using "encoding/json"

  1. type CourseAssignment struct {
  2.     Semester int `json:&quot;semester&quot;  xml:&quot;semester&quot;`
  3.     Lecture Lecture `json:&quot;-&quot;  xml:&quot;-&quot;`
  4.     Cos Cos `json:&quot;-&quot;  xml:&quot;-&quot;`
  5.     Links map[string][]Link `json:&quot;links,omitempty&quot; xml:&quot;links,omitempty&quot;`
  6. }

Lecture and Cos are complex structs themselves that i dont want to be included in my serialized json which i indicate by setting json:"-"

This works perfectly.

How do I override that behavior on demand during runtime, without writing my own Serialization code?

My Own Solution:

  1. func (r *CourseAssignment) Expand(depth int) CourseAssignment {
  3. 	if depth &lt;= 0 {
  4. 		return *r
  5. 	}
  7. 	tmp := *r
  8. 	tmp.LectureEx = tmp.Lecture
  9. 	tmp.CosEx = tmp.Cos
  10. 	tmp.Links = nil	
  11. 	return tmp
  12. }
  14. type CourseAssignment struct {
  15. 	Semester int `json:&quot;semester&quot;  xml:&quot;semester&quot;`
  16. 	Lecture *Lecture `json:&quot;-&quot;  xml:&quot;-&quot;`
  17. 	Cos *Cos `json:&quot;-&quot;  xml:&quot;-&quot;`
  18. 	Links map[string][]Link `json:&quot;links,omitempty&quot; xml:&quot;links,omitempty&quot;`
  19. 	LectureEx  *Lecture   `json:&quot;lecture,omitempty&quot;  xml:&quot;lecture,omitempty&quot;`
  20. 	CosEx *Cos `json:&quot;course_of_study,omitempty&quot; xml:&quot;course_of_study,omitempty&quot;`	
  21. }

When I want to include the fields, I create a Copy of the Object using Expand that fills fields that contain the same references but show up in the serialization.

答案1

得分: 4

你可以使用reflect包中的StructTag来读取/获取结构体标签的值：

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"reflect"
  6. )
  8. type CourseAssignment struct {
  9. 	Semester int `json:"semester"  xml:"semester"`
  10. }
  12. func main() {
  13. 	ca := CourseAssignment{}
  14. 	st := reflect.TypeOf(ca)
  15. 	field := st.Field(0)
  16. 	fmt.Println(field.Tag.Get("json"))
  17. }

标准库中没有提供直接修改结构体标签字段的方法。

然而，有一些开源库可以实现这一功能，比如Retag。

英文:

You can read/get struct tag values using StructTag from reflect package:

  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  5. 	&quot;reflect&quot;
  6. )
  8. type CourseAssignment struct {
  9. 	Semester int `json:&quot;semester&quot;  xml:&quot;semester&quot;`
  10. }
  12. func main() {
  13. 	ca := CourseAssignment{}
  14. 	st := reflect.TypeOf(ca)
  15. 	field := st.Field(0)
  16. 	fmt.Println(field.Tag.Get(&quot;json&quot;))
  17. }

There is no method to change a struct tag field in the standard library.

However, there are open-source libraries that do exactly that, like Retag.

答案2

得分: 0

在类似情况下，我通常会将这些字段设置为omitempty，然后在不希望它们包含在JSON中的情况下将其置为空：

  1. type CourseAssignment struct {
  2.     Semester int `json:"semester" xml:"semester"`
  3.     Lecture *Lecture `json:"lecture,omitempty" xml:"-"`
  4.     Cos *Cos `json:"cos,omitempty" xml:"-"`
  5.     Links map[string][]Link `json:"links,omitempty" xml:"links,omitempty"`
  6. }
  8. // 不包含Lecture/Cos进行序列化：
  9. aCourseAssignment.Lecture = nil
  10. aCourseAssignment.Cos = nil
  11. thing, err := json.Marshal(aCourseAssignment)

以上是代码的翻译部分。

英文:

What I've done in similar cases is to set these kinds of fields to omitempty, and then empty them before serializing in the cases where I don't want them included in JSON:

  1. type CourseAssignment struct {
  2.     Semester int `json:&quot;semester&quot;  xml:&quot;semester&quot;`
  3.     Lecture *Lecture `json:&quot;lecture,omitempty&quot;  xml:&quot;-&quot;`
  4.     Cos *Cos `json:&quot;cos,omitempty&quot;  xml:&quot;-&quot;`
  5.     Links map[string][]Link `json:&quot;links,omitempty&quot; xml:&quot;links,omitempty&quot;`
  6. }
  8. // Want to serialize without including Lecture/Cos:
  9. aCourseAssignment.Lecture = nil
  10. aCourseAssignment.Cos = nil
  11. thing,err := json.Marshal(aCourseAssignment)

huangapple
  • 本文由 发表于 2017年7月11日 18:53:36
  • 转载请务必保留本文链接：https://go.coder-hub.com/45032514.html
  • go
  • json
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定