Golang在解组后访问嵌套的JSON数组的问题

huangapple
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英文:

Golang issue with accessing Nested JSON Array after Unmarshalling

问题

我还在学习Go语言的过程中，但在处理JSON响应数组时遇到了问题。每当我尝试访问"objects"数组的嵌套元素时，Go会抛出错误（类型interface {}不支持索引）。

出了什么问题，我如何避免将来犯同样的错误？

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. )
  8. func main() {
  9. 	payload := []byte(`{"query": "QEACOR139GID","count": 1,"objects": [{"ITEM_ID": "QEACOR139GID","PROD_CLASS_ID": "BMXCPGRIPS","AVAILABLE": 19}]}`)
  10. 	var result map[string]interface{}
  11. 	if err := json.Unmarshal(payload, &result); err != nil {
  12. 		panic(err)
  13. 	}
  15. 	objects := result["objects"].([]interface{})
  16. 	firstObject := objects[0].(map[string]interface{})
  17. 	fmt.Println(firstObject["ITEM_ID"])
  18. }

链接：http://play.golang.org/p/duW-meEABJ

编辑：修复了链接。

英文:

I'm still in the learning process of Go but am hitting a wall when it comes to JSON response arrays. Whenever I try to access a nested element of the "objects" array, Go throws (type interface {} does not support indexing)

What is going wrong and how can I avoid making this mistake in the future?

  1. package main    
  3. import (
  4.     	"encoding/json"
  5.     	"fmt"
  6. )    
  8. func main() {
  9.     	payload := []byte(`{"query": "QEACOR139GID","count": 1,"objects": [{"ITEM_ID": "QEACOR139GID","PROD_CLASS_ID": "BMXCPGRIPS","AVAILABLE": 19}]}`)
  10.     	var result map[string]interface{}
  11.     	if err := json.Unmarshal(payload, &result); err != nil {
  12.     		panic(err)
  13.     	}        
  15.     	fmt.Println(result["objects"]["ITEM_ID"])    
  17. }

http://play.golang.org/p/duW-meEABJ

edit: Fixed link

答案1

得分: 28

根据错误提示，接口变量不支持索引。你需要使用类型断言将其转换为底层类型。

在解码为interface{}变量时，JSON模块将数组表示为[]interface{}切片，将字典表示为map[string]interface{}映射。

如果没有错误检查，你可以使用以下代码深入到这个JSON中：

  1. objects := result["objects"].([]interface{})
  2. first := objects[0].(map[string]interface{})
  3. fmt.Println(first["ITEM_ID"])

如果类型不匹配，这些类型断言将会引发恐慌。你可以使用两个返回值的形式来检查错误。例如：

  1. objects, ok := result["objects"].([]interface{})
  2. if !ok {
  3.     // 在这里处理错误
  4. }

如果JSON遵循已知的格式，更好的解决方案是解码为一个结构体。根据你的示例数据，以下代码可能适用：

  1. type Result struct {
  2.     Query   string `json:"query"`
  3.     Count   int    `json:"count"`
  4.     Objects []struct {
  5.         ItemId      string `json:"ITEM_ID"`
  6.         ProdClassId string `json:"PROD_CLASS_ID"`
  7.         Available   int    `json:"AVAILABLE"`
  8.     } `json:"objects"`
  9. }

如果你解码为这种类型，可以通过result.Objects[0].ItemId访问项目ID。

英文:

As the error says, interface variables do not support indexing. You will need to use a type assertion to convert to the underlying type.

When decoding into an interface{} variable, the JSON module represents arrays as []interface{} slices and dictionaries as map[string]interface{} maps.

Without error checking, you could dig down into this JSON with something like:

  1. objects := result["objects"].([]interface{})
  2. first := objects[0].(map[string]interface{})
  3. fmt.Println(first["ITEM_ID"])

These type assertions will panic if the types do not match. You can use the two-return form, you can check for this error. For example:

  1. objects, ok := result["objects"].([]interface{})
  2. if !ok {
  3. 	// Handle error here
  4. }

If the JSON follows a known format though, a better solution would be to decode into a structure. Given the data in your example, the following might do:

  1. type Result struct {
  2. 	Query   string `json:"query"`
  3. 	Count   int    `json:"count"`
  4. 	Objects []struct {
  5. 		ItemId      string `json:"ITEM_ID"`
  6. 		ProdClassId string `json:"PROD_CLASS_ID"`
  7. 		Available   int    `json:"AVAILABLE"`
  8. 	} `json:"objects"`
  9. }

If you decode into this type, you can access the item ID as result.Objects[0].ItemId.

答案2

得分: 0

对于那些可能正在寻找与我类似解决方案的人，https://github.com/Jeffail/gabs 提供了更好的解决方案。

我在这里提供一个示例。

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  7. 	"github.com/Jeffail/gabs"
  8. )
  10. func main() {
  11. 	payload := []byte(`{
  12. 		"query": "QEACOR139GID",
  13. 		"count": 1,
  14. 		"objects": [{
  15. 			"ITEM_ID": "QEACOR139GID",
  16. 			"PROD_CLASS_ID": "BMXCPGRIPS",
  17. 			"AVAILABLE": 19,
  18. 			"Messages": [{
  19. 					"first": {
  20. 						"text": "sth, 1st"
  21. 					}
  22. 				},
  23. 				{
  24. 					"second": {
  25. 						"text": "sth, 2nd"
  26. 					}
  27. 				}
  28. 			]
  29. 		}]
  30. 	}`)
  32. 	fmt.Println("使用 gabs：")
  33. 	jsonParsed, _ := gabs.ParseJSON(payload)
  34. 	data := jsonParsed.Path("objects").Data()
  35. 	fmt.Println("  获取数据：")
  36. 	fmt.Println("    ", data)
  37. 	children, _ := jsonParsed.Path("objects").Children()
  38. 	fmt.Println("  从\"objects\"获取的子数组：")
  39. 	for key, child := range children {
  40. 		fmt.Println("    ", key, ":", child)
  41. 		children2, _ := child.Path("Messages").Children()
  42. 		fmt.Println("    从\"Messages\"获取的子数组：")
  43. 		for key2, child2 := range children2 {
  44. 			fmt.Println("      ", key2, ":", child2)
  45. 		}
  46. 	}
  47. }
英文:

For who those might looking for similar solution like me, https://github.com/Jeffail/gabs provides better solution.

I provide the example here.

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  7. 	"github.com/Jeffail/gabs"
  8. )
  10. func main() {
  11. 	payload := []byte(`{
  12. 		"query": "QEACOR139GID",
  13. 		"count": 1,
  14. 		"objects": [{
  15. 			"ITEM_ID": "QEACOR139GID",
  16. 			"PROD_CLASS_ID": "BMXCPGRIPS",
  17. 			"AVAILABLE": 19, 
  18. 			"Messages": [ {
  19. 					"first": {
  20. 						"text":  "sth, 1st"
  21. 					}
  22. 				},
  23. 				{
  24. 						"second": {
  25. 						"text": "sth, 2nd"
  26. 					}
  27. 			  }
  28. 			]
  29. 		}]
  30. 	}`)
  32. 	fmt.Println("Use gabs:")
  33. 	jsonParsed, _ := gabs.ParseJSON(payload)
  34. 	data := jsonParsed.Path("objects").Data()
  35. 	fmt.Println("  Fetch Data: ")
  36. 	fmt.Println("    ", data)
  37. 	children, _ := jsonParsed.Path("objects").Children()
  38. 	fmt.Println("  Children Array from \"Objects\": ")
  39. 	for key, child := range children {
  40. 		fmt.Println("    ", key, ": ", child)
  41. 		children2, _ := child.Path("Messages").Children()
  42. 		fmt.Println("    Children Array from \"Messages\": ")
  43. 		for key2, child2 := range children2 {
  44. 			fmt.Println("      ", key2, ": ", child2)
  45. 		}
  46. 	}
  47. }

huangapple
  • 本文由 发表于 2014年6月24日 11:32:18
  • 转载请务必保留本文链接：https://go.coder-hub.com/24377907.html
  • go
  • json
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