如何读取具有结构体地址的接口值

huangapple
go评论96阅读模式
英文:

How read interface value having address of struct

问题

我有一个数据类型为interface{}的变量，并将结构体的地址传递给它。现在我无法从接口中读取字段。

以下是代码：

  1. type UserData struct {
  2.     UserID   string `json:"user_id"`
  3.     UserName string `json:"user_name"`
  4. }
  6. type Result struct {
  7.     Status string      `json:"status"`
  8.     Data   interface{} `json:"data"`
  9. }
  11. var res Result
  12. res.Data = &UserData{}
  13. json.Unmarshal([]byte(`{"status": "success", "data": {"user_id":15,"user_name":"abc"}}`), &res)
  14. fmt.Println(res.Data) // 正常工作
  15. fmt.Println(res.Data.UserName) // 出错：类型interface{}没有字段或方法UserName

如果我使用res.Data.UserName会出错。

如何从接口中读取结构体字段？

英文:

I have variable with data type interface{} and passing address of struct to it. now I unable read fields from interface

code as below:

  1. type UserData struct {
  2.     UserID string `json:"user_id"`
  3.     UserName string `json:"user_name"`
  4. }
  6. type Result struct {
  7.     Status string `json:"status"`
  8.     Data interface{} `json:"data"`
  9. }
  11. var res Result
  12. res.Data = &UserData
  13. json.Unmarshal([]byte(`{"status": "success", "data": {"user_id":15,"user_name":"abc"}}`), &res)
  14. fmt.Println(res.Data) //working fine
  15. fmt.Println(res.Data.UserName) //getting error: type interface{} has no field or method UserName

if I use res.Data.UserName getting error

How to read struct fields from interface?

答案1

得分: 2

这与https://stackoverflow.com/questions/76284655/golang-why-does-field-not-existed-in-go-struct-still-present-after-marshaling-sa进行比较很有趣。起初我以为它们是相同的。但事实证明它们并不相同。

对于这个问题，res.Data保存的是*UserData类型的值。所以一个简单的类型断言就可以解决。

以下是一个示例代码，合并了@mkopriva的两个示例，并展示了它们之间的区别：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. )
  9. type DBBatch struct {
  10. 	FieldtoKeep  string `json:"field_to_keep"`
  11. 	FieldtoKeep2 string `json:"field_to_keep2"`
  12. }
  14. func main() {
  15. 	jsonBatch := `{"field_to_keep":"XXXXX","field_to_keep2":"26400527","field_to_delete":"whynotdeleted"}`
  16. 	var i interface{} = DBBatch{}
  17. 	fmt.Printf("%T\n", i) // 类型是DBBatch
  18. 	if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
  19. 		log.Println(err)
  20. 	}
  21. 	fmt.Printf("%T\n", i) // 类型不再是DBBatch，而是map[string]interface{}
  23. 	i = &DBBatch{}
  24. 	fmt.Printf("%T\n", i) // 类型是*DBBatch
  25. 	if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
  26. 		log.Println(err)
  27. 	}
  28. 	fmt.Printf("%T\n", i) // 类型是*DBBatch
  29. }

输出结果为：

  1. main.DBBatch
  2. map[string]interface {}
  3. *main.DBBatch
  4. *main.DBBatch
英文:

It's interesting to compare this with https://stackoverflow.com/questions/76284655/golang-why-does-field-not-existed-in-go-struct-still-present-after-marshaling-sa. At first I thought they are the same. But it turns out that they are not.

For this question, res.Data holds a value of type *UserData. So a simple type assertion will work.

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. )
  8. type UserData struct {
  9. 	UserID   string `json:"user_id"`
  10. 	UserName string `json:"user_name"`
  11. }
  13. type Result struct {
  14. 	Status string      `json:"status"`
  15. 	Data   interface{} `json:"data"`
  16. }
  18. func main() {
  19. 	var res Result
  20. 	res.Data = &UserData{}
  21. 	json.Unmarshal([]byte(`{"status": "success", "data": {"user_id":15,"user_name":"abc"}}`), &res)
  22. 	fmt.Println(res.Data)
  23. 	fmt.Println(res.Data.(*UserData).UserName)
  24. }

The following demo is a merge of @mkopriva's two demos, and it shows the difference:

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"log"
  7. )
  9. type DBBatch struct {
  10. 	FieldtoKeep  string `json:"field_to_keep"`
  11. 	FieldtoKeep2 string `json:"field_to_keep2"`
  12. }
  14. func main() {
  15. 	jsonBatch := `{"field_to_keep":"XXXXX","field_to_keep2":"26400527","field_to_delete":"whynotdeleted"}`
  16. 	var i interface{} = DBBatch{}
  17. 	fmt.Printf("%T\n", i) // type is DBBatch
  18. 	if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
  19. 		log.Println(err)
  20. 	}
  21. 	fmt.Printf("%T\n", i) // type is not DBBatch anymore, instead it's map[string]any
  23. 	i = &DBBatch{}
  24. 	fmt.Printf("%T\n", i) // type is *DBBatch
  25. 	if err := json.Unmarshal([]byte(jsonBatch), &i); err != nil {
  26. 		log.Println(err)
  27. 	}
  28. 	fmt.Printf("%T\n", i) // type is *DBBatch
  29. }

The output is:

  1. main.DBBatch
  2. map[string]interface {}
  3. *main.DBBatch
  4. *main.DBBatch

huangapple
  • 本文由 发表于 2023年5月27日 16:43:01
  • 转载请务必保留本文链接：https://go.coder-hub.com/76346054.html
  • go
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