在Go语言中解组对象数组。

huangapple
go评论116阅读模式
英文:

Unmarshaling array of objects in Go

问题

在GO语言中，我尝试生成以下JSON：

[["my",257.14,257.24],["txt", 121.11, 65.555]]

但在进行解组时失败了。

这是我尝试的代码：

x := []MyStruct{{Zero: map[int]string{0: "str"}, One: map[int]float32{1: 5.6}, Two: map[int]float32{1: 5.88}}}

其中MyStruct定义如下：

type Timestamp struct {
Zero map[int]string json:"0"
One map[int]float32 json:"1"
Two map[int]float32 json:"2"
}

这会生成错误的JSON结构：

"myStruct":[{"0":{"0":"has"},"1":{"1":5.6},"2":{"1":5.88}}]

我也尝试了这个解答。

如果有任何指导方向，将不胜感激。

英文:

in GO, I've tried to produce the following json :

  1. [["my",257.14,257.24],["txt", 121.11, 65.555]]

from a struct that's undergo unmarshaling - and i'm failing to do so.

Here is what I tried:

  1. x := []MyStruct{{Zero: map[int]string{0: "str"}, One: map[int]float32{1: 5.6}, Two: map[int]float32{1: 5.88}}}

where MyStruct is :

  1. type Timestamp struct {
  2.   Zero		map[int]string		`json:"0"`
  3.   One		map[int]float32		`json:"1"`
  4.   Two		map[int]float32		`json:"2"`
  5. }

this produces the wrong json structure:

  1. "myStruct":[{"0":{"0":"has"},"1":{"1":5.6},"2":{"1":5.88}}]

tried this as well

any clue in the right direction will be highly appreciated.

答案1

得分: 4

也许这是你期望的。可以实现自定义的MarshalJSON/UnmarshalJSON。

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"errors"
  6. 	"fmt"
  7. 	"log"
  8. )
  10. type Timestamp struct {
  11. 	Zero []string
  12. 	One  []float32
  13. 	Two  []float32
  14. }
  16. func (t *Timestamp) UnmarshalJSON(b []byte) error {
  17. 	var arr [][3]interface{}
  18. 	err := json.Unmarshal(b, &arr)
  19. 	if err != nil {
  20. 		return nil
  21. 	}
  22. 	t.Zero = nil
  23. 	t.One = nil
  24. 	t.Two = nil
  25. 	for _, v := range arr {
  26. 		if len(v) != 3 {
  27. 			return errors.New("invalid json")
  28. 		}
  29. 		if s, ok := v[0].(string); ok {
  30. 			t.Zero = append(t.Zero, s)
  31. 		}
  32. 		if f, ok := v[1].(float64); ok {
  33. 			t.One = append(t.One, float32(f))
  34. 		}
  35. 		if f, ok := v[2].(float64); ok {
  36. 			t.Two = append(t.Two, float32(f))
  37. 		}
  38. 	}
  39. 	return nil
  40. }
  42. func (t *Timestamp) MarshalJSON() ([]byte, error) {
  43. 	var arr [][3]interface{}
  44. 	var max int
  45. 	if max < len(t.Zero) {
  46. 		max = len(t.Zero)
  47. 	}
  48. 	if max < len(t.One) {
  49. 		max = len(t.One)
  50. 	}
  51. 	if max < len(t.Two) {
  52. 		max = len(t.Two)
  53. 	}
  54. 	for i := 0; i < max; i++ {
  55. 		var v [3]interface{}
  56. 		if i < len(t.Zero) {
  57. 			v[0] = t.Zero[i]
  58. 		}
  59. 		if i < len(t.One) {
  60. 			v[1] = t.One[i]
  61. 		}
  62. 		if i < len(t.Two) {
  63. 			v[2] = t.Two[i]
  64. 		}
  65. 		arr = append(arr, v)
  66. 	}
  67. 	return json.Marshal(arr)
  68. }
  70. const j = `[["my",257.14,257.24],["txt", 121.11, 65.555]]`
  72. func main() {
  73. 	var ts Timestamp
  74. 	err := json.Unmarshal([]byte(j), &ts)
  75. 	if err != nil {
  76. 		log.Fatal(err)
  77. 	}
  78. 	b, err := json.Marshal(&ts)
  79. 	if err != nil {
  80. 		log.Fatal(err)
  81. 	}
  82. 	fmt.Println(string(b))
  83. }

链接：https://play.golang.org/p/WtVEja1JDY

英文:

Maybe this is your expected. It's possible to implement custom MarshalJSON/UnmarshalJSON.

  1. package main
  2. import (
  3. &quot;encoding/json&quot;
  4. &quot;errors&quot;
  5. &quot;fmt&quot;
  6. &quot;log&quot;
  7. )
  8. type Timestamp struct {
  9. Zero []string
  10. One  []float32
  11. Two  []float32
  12. }
  13. func (t *Timestamp) UnmarshalJSON(b []byte) error {
  14. var arr [][3]interface{}
  15. err := json.Unmarshal(b, &amp;arr)
  16. if err != nil {
  17. return nil
  18. }
  19. t.Zero = nil
  20. t.One = nil
  21. t.Two = nil
  22. for _, v := range arr {
  23. if len(v) != 3 {
  24. return errors.New(&quot;invalid json&quot;)
  25. }
  26. if s, ok := v[0].(string); ok {
  27. t.Zero = append(t.Zero, s)
  28. }
  29. if f, ok := v[1].(float64); ok {
  30. t.One = append(t.One, float32(f))
  31. }
  32. if f, ok := v[2].(float64); ok {
  33. t.Two = append(t.Two, float32(f))
  34. }
  35. }
  36. return nil
  37. }
  38. func (t *Timestamp) MarshalJSON() ([]byte, error) {
  39. var arr [][3]interface{}
  40. var max int
  41. if max &lt; len(t.Zero) {
  42. max = len(t.Zero)
  43. }
  44. if max &lt; len(t.One) {
  45. max = len(t.One)
  46. }
  47. if max &lt; len(t.Two) {
  48. max = len(t.Two)
  49. }
  50. for i := 0; i &lt; max; i++ {
  51. var v [3]interface{}
  52. if i &lt; len(t.Zero) {
  53. v[0] = t.Zero[i]
  54. }
  55. if i &lt; len(t.One) {
  56. v[1] = t.One[i]
  57. }
  58. if i &lt; len(t.Two) {
  59. v[2] = t.Two[i]
  60. }
  61. arr = append(arr, v)
  62. }
  63. return json.Marshal(arr)
  64. }
  65. const j = `[[&quot;my&quot;,257.14,257.24],[&quot;txt&quot;, 121.11, 65.555]]`
  66. func main() {
  67. var ts Timestamp
  68. err := json.Unmarshal([]byte(j), &amp;ts)
  69. if err != nil {
  70. log.Fatal(err)
  71. }
  72. b, err := json.Marshal(&amp;ts)
  73. if err != nil {
  74. log.Fatal(err)
  75. }
  76. fmt.Println(string(b))
  77. }

https://play.golang.org/p/WtVEja1JDY

答案2

得分: 2

你遇到的问题是你试图解组一个映射（map），而映射会对应一个 JSON 对象。你期望的输出是一个列表，所以你需要解组一个数组或切片来获取一个列表作为你的值。

尝试创建一个适配器。

以下是一个简单的示例：

  1. type Object struct {
  2.     Base   float32 
  3.     Radius float32 
  4.     Height float32 
  5.     X      float32 
  6.     Y      float32 
  7. }
  9. func (obj *Object) ToCircle() *Circle {
  10.     return &Circle{
  11.         Radius: obj.Radius,
  12.         X:      obj.X,
  13.         Y:      obj.Y,
  14.     }
  15. }
  17. func (obj *Object) ToRectangle() *Rectangle {
  18.     return &Rectangle{
  19.         Base:   obj.Base,
  20.         Height: obj.Height,
  21.         X:      obj.X,
  22.         Y:      obj.Y,
  23.     }
  24. }

在上面的示例中，Object 通过 ToRectangle() 和 ToCircle() 适配器分别转换为 Rectangle 或 Circle。在你的情况下，你需要将 Timestamp 转换为 []interface{}。然后你可以解组，你将得到一个包含在该切片中的任何值的列表，这是你在这种情况下期望的输出。

例如，你的适配器的签名可以是这样的：

  1. func (t *Timestamp) ToFoo() []interface{} {
  2.     var ret []interface{}
  4.     // 做一些处理，将 't' 的值添加到 'ret' 中
  6.     return ret
  7. }
  9. func main() {
  10.     var result []interface{}
  12.     json.Unmarshal(t.ToFoo(), &result)
  14.     // ...
  15. }

具体的实现细节留给你来完成。

英文:

The problem you are having is you're trying to unmarshal a map, and a map will correlate to a JSON object. Your desired output is a list, so you need to unmarshal an array or a slice to get a list as your values.

Try making an adapter.

Small example:

  1. type Object struct {
  2. Base   float32 
  3. Radius float32 
  4. Height float32 
  5. X      float32 
  6. Y      float32 
  7. }
  8. func (obj *Object) ToCircle() *Circle {
  9. return &amp;Circle{
  10. Radius: obj.Radius,
  11. X:      obj.X,
  12. Y:      obj.Y,
  13. }
  14. }
  15. func (obj *Object) ToRectangle() *Rectangle {
  16. return &amp;Rectangle{
  17. Base:   obj.Base,
  18. Height: obj.Height,
  19. X:      obj.X,
  20. Y:      obj.Y,
  21. }
  22. }

In the example above, Object is converted to a Rectangle or a Circle using the ToRectangle() and ToCircle() adapters, respectively. In your case, you need to convert Timestamp to a []interface{}. Then you can unmarshal and you'll just get a list of whatever values are in that slice, which is your desired output in this case.

For intsance, the signature if your adapter could look like this:

  1. func (t *Timestamp) ToFoo() []interface{} {
  2. var ret []interface{}
  3. // Do some stuff to take values of &#39;t&#39; and append to &#39;ret&#39;
  4. return ret
  5. }
  6. func main() {
  7. var result []interface{}
  8. json.Unmarshal(t.ToFoo(), &amp;result)
  9. // ...
  10. }

I'll leave the implementation details for you.

huangapple
  • 本文由 发表于 2017年7月3日 23:31:50
  • 转载请务必保留本文链接：https://go.coder-hub.com/44889361.html
  • arrays
  • 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