适合解析geojson的结构类型

huangapple
go评论126阅读模式
英文:

Suitable struct type for unmarshal of geojson

问题

我想将一个geojson字符串解组成适当的结构类型。
我有三个不同的geojson字符串，我想将它们解组成相同的结构体：

  1. var jsonBlobPointString = []byte(`{"Type":"Point", "Coordinates":[1.1,2.0]}`)
  2. var jsonBlobLineString = []byte(`{"Type":"LineString", "Coordinates":[[1.1,2.0],[3.0,6.3]]}`)
  3. var jsonBlobPolygonString = []byte(`{"Type":"Polygon", "Coordinates":[[[1.1,2.0],[3.0,6.3],[5.1,7.0],[1.1,2.0]]]}`)

我想出了一个结构类型，但我对它不完全满意：

  1. type GeojsonType struct {
  2.     Type string
  3.     Coordinates interface{}
  4. }

请参考此链接获取完整示例：
http://play.golang.org/p/Bt-51BX__A

我不想使用interface{}作为Coordinates的类型。
我希望使用一些可以为Point提供一些验证的东西，例如Coordinates []float64，
以及LineString的Coordinates [][]float64。

是否可能创建一个结构类型，使得Point、LineString和Polygon都可以在Coordinates中表示，而不使用interface？

英文:

I want to unmarshal a geojson string into a suitable struct type.
I have three different geojson strings that I want to unmarshal into the same struct:

  1. var jsonBlobPointString = []byte(`{"Type":"Point", "Coordinates":[1.1,2.0]}`)
  2. var jsonBlobLineString = []byte(`{"Type":"LineString", "Coordinates":[[1.1,2.0],[3.0,6.3]]}`)
  3. var jsonBlobPolygonString = []byte(`{"Type":"Polygon", "Coordinates":[[[1.1,2.0],[3.0,6.3],[5.1,7.0],[1.1,2.0]]]}`)

I came up with a struct type that I´m not totally happy with:

  1. type GeojsonType struct {
  2.     Type string
  3.     Coordinates interface{}
  4. }

See this link for complete example:
http://play.golang.org/p/Bt-51BX__A

I would rather not use interface{} for Coordinates.
I would instead use somehting that give me some validation for example Coordinates [] float64 for Point
and Coordinates[][] float64 for LineString.

Is it possible to create a struct type so that Point, LineString and Polygon all can be represented in Coordinates without using interface?

答案1

得分: 9

你想要的是从同一个json字典中创建3种不同类型的对象。

据我所知，这是不可能的，但是你可以使用RawMessage类型来延迟json解码，并使用一些预处理像这样

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. )
  8. type Point struct {
  9. 	Coordinates []float64
  10. }
  12. type Line struct {
  13. 	Points [][]float64
  14. }
  16. type Polygon struct {
  17. 	Lines [][][]float64
  18. }
  20. type GeojsonType struct {
  21. 	Type        string
  22. 	Coordinates json.RawMessage
  23. 	Point       Point
  24. 	Line        Line
  25. 	Polygon     Polygon
  26. }
  28. var jsonBlob = []byte(`[
  29. {"Type":"Point", "Coordinates":[1.1,2.0]},
  30. {"Type":"LineString", "Coordinates":[[1.1,2.0],[3.0,6.3]]},
  31. {"Type":"Polygon", "Coordinates":[[[1.1,2.0],[3.0,6.3],[5.1,7.0],[1.1,2.0]]]}
  32. ]`)
  34. func main() {
  35. 	var geojsonPoints []GeojsonType
  36. 	err := json.Unmarshal(jsonBlob, &geojsonPoints)
  37. 	if err != nil {
  38. 		fmt.Println("error:", err)
  39. 	}
  41. 	// 后处理坐标
  43. 	for i := range geojsonPoints {
  44. 		t := &geojsonPoints[i]
  46. 		switch t.Type {
  47. 		case "Point":
  48. 			err = json.Unmarshal(t.Coordinates, &t.Point.Coordinates)
  49. 		case "LineString":
  50. 			err = json.Unmarshal(t.Coordinates, &t.Line.Points)
  51. 		case "Polygon":
  52. 			err = json.Unmarshal(t.Coordinates, &t.Polygon.Lines)
  53. 		default:
  54. 			panic("Unknown type")
  55. 		}
  56. 		if err != nil {
  57. 			fmt.Printf("Failed to convert %s: %s", t.Type, err)
  58. 		}
  59. 		fmt.Printf("%+v\n", t)
  60. 	}
  61. }

打印结果为

  1. &{Type:Point Coordinates:[91 49 46 49 44 50 46 48 93] Point:{Coordinates:[1.1 2]} Line:{Points:[]} Polygon:{Lines:[]}}
  2. &{Type:LineString Coordinates:[91 91 49 46 49 44 50 46 48 93 44 91 51 46 48 44 54 46 51 93 93] Point:{Coordinates:[]} Line:{Points:[[1.1 2] [3 6.3]]} Polygon:{Lines:[]}}
  3. &{Type:Polygon Coordinates:[91 91 91 49 46 49 44 50 46 48 93 44 91 51 46 48 44 54 46 51 93 44 91 53 46 49 44 55 46 48 93 44 91 49 46 49 44 50 46 48 93 93 93] Point:{Coordinates:[]} Line:{Points:[]} Polygon:{Lines:[[[1.1 2] [3 6.3] [5.1 7] [1.1 2]]]}}
英文:

What you want is to create 3 different types of object from the same json dictionary.

As far as I know that isn't possible, however you can use the RawMessage type to delay the json decoding and use a bit of pre-processing like this

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. )
  8. type Point struct {
  9. 	Coordinates []float64
  10. }
  12. type Line struct {
  13. 	Points [][]float64
  14. }
  16. type Polygon struct {
  17. 	Lines [][][]float64
  18. }
  20. type GeojsonType struct {
  21. 	Type        string
  22. 	Coordinates json.RawMessage
  23. 	Point       Point
  24. 	Line        Line
  25. 	Polygon     Polygon
  26. }
  28. var jsonBlob = []byte(`[
  29. {"Type":"Point", "Coordinates":[1.1,2.0]},
  30. {"Type":"LineString", "Coordinates":[[1.1,2.0],[3.0,6.3]]},
  31. {"Type":"Polygon", "Coordinates":[[[1.1,2.0],[3.0,6.3],[5.1,7.0],[1.1,2.0]]]}
  32. ]`)
  34. func main() {
  35. 	var geojsonPoints []GeojsonType
  36. 	err := json.Unmarshal(jsonBlob, &geojsonPoints)
  37. 	if err != nil {
  38. 		fmt.Println("error:", err)
  39. 	}
  41. 	// Postprocess the coordinates	
  43. 	for i := range geojsonPoints {
  44. 		t := &geojsonPoints[i]
  46. 		switch t.Type {
  47. 		case "Point":
  48. 			err = json.Unmarshal(t.Coordinates, &t.Point.Coordinates)
  49. 		case "LineString":
  50. 			err = json.Unmarshal(t.Coordinates, &t.Line.Points)
  51. 		case "Polygon":
  52. 			err = json.Unmarshal(t.Coordinates, &t.Polygon.Lines)
  53. 		default:
  54. 			panic("Unknown type")
  55. 		}
  56. 		if err != nil {
  57. 			fmt.Printf("Failed to convert %s: %s", t.Type, err)
  58. 		}
  59. 		fmt.Printf("%+v\n", t)
  60. 	}
  61. }

Which prints

  1. &{Type:Point Coordinates:[91 49 46 49 44 50 46 48 93] Point:{Coordinates:[1.1 2]} Line:{Points:[]} Polygon:{Lines:[]}}
  2. &{Type:LineString Coordinates:[91 91 49 46 49 44 50 46 48 93 44 91 51 46 48 44 54 46 51 93 93] Point:{Coordinates:[]} Line:{Points:[[1.1 2] [3 6.3]]} Polygon:{Lines:[]}}
  3. &{Type:Polygon Coordinates:[91 91 91 49 46 49 44 50 46 48 93 44 91 51 46 48 44 54 46 51 93 44 91 53 46 49 44 55 46 48 93 44 91 49 46 49 44 50 46 48 93 93 93] Point:{Coordinates:[]} Line:{Points:[]} Polygon:{Lines:[[[1.1 2] [3 6.3] [5.1 7] [1.1 2]]]}}

答案2

得分: 3

基于Nick Craig-Wood的答案，我构建了以下的Marshal/UnMarshal函数。

  1. package geojson
  3. //https://stackoverflow.com/questions/15719532/suitable-struct-type-for-unmarshal-of-geojson
  5. import (
  6. 	"encoding/json"
  7. )
  9. type Point struct {
  10. 	Coordinates []float64
  11. }
  13. type Line struct {
  14. 	Points [][]float64
  15. }
  17. type Polygon struct {
  18. 	Lines [][][]float64
  19. }
  21. type Geojson struct {
  22. 	Type        string          `json:"type"`
  23. 	Coordinates json.RawMessage `json:"coordinates"`
  24. 	Point       Point           `json:"-"`
  25. 	Line        Line            `json:"-"`
  26. 	Polygon     Polygon         `json:"-"`
  27. }
  29. func (g *Geojson) UnmarshalJSON(b []byte) error {
  31. 	type Alias Geojson
  32. 	aux := (*Alias)(g)
  34. 	err := json.Unmarshal(b, &aux)
  36. 	if err != nil {
  37. 		return err
  38. 	}
  40. 	switch g.Type {
  41. 	case "Point":
  42. 		err = json.Unmarshal(g.Coordinates, &g.Point.Coordinates)
  43. 	case "LineString":
  44. 		err = json.Unmarshal(g.Coordinates, &g.Line.Points)
  45. 	case "Polygon":
  46. 		err = json.Unmarshal(g.Coordinates, &g.Polygon.Lines)
  47. 	}
  49. 	g.Coordinates = []byte(nil)
  51. 	return err
  52. }
  54. func (g Geojson) MarshalJSON() ([]byte, error) {
  56. 	var raw json.RawMessage
  57. 	var err error
  59. 	switch g.Type {
  60. 	case "Point":
  61. 		raw, err = json.Marshal(&g.Point.Coordinates)
  62. 	case "LineString":
  63. 		raw, err = json.Marshal(&g.Line.Points)
  64. 	case "Polygon":
  65. 		raw, err = json.Marshal(&g.Polygon.Lines)
  66. 	}
  68. 	if err != nil {
  69. 		return nil, err
  70. 	}
  72. 	g.Coordinates = raw
  74. 	type Alias Geojson
  75. 	aux := (*Alias)(&g)
  76. 	return json.Marshal(aux)
  77. }
英文:

Based on Nick Craig-Wood answer I built the following Marshal/UnMarshal functions

  1. package geojson
  3. //https://stackoverflow.com/questions/15719532/suitable-struct-type-for-unmarshal-of-geojson
  5. import (
  6. 	"encoding/json"
  7. )
  9. type Point struct {
  10. 	Coordinates []float64
  11. }
  13. type Line struct {
  14. 	Points [][]float64
  15. }
  17. type Polygon struct {
  18. 	Lines [][][]float64
  19. }
  21. type Geojson struct {
  22. 	Type        string          `json:"type"`
  23. 	Coordinates json.RawMessage `json:"coordinates"`
  24. 	Point       Point           `json:"-"`
  25. 	Line        Line            `json:"-"`
  26. 	Polygon     Polygon         `json:"-"`
  27. }
  29. func (g *Geojson) UnmarshalJSON(b []byte) error {
  31. 	type Alias Geojson
  32. 	aux := (*Alias)(g)
  34. 	err := json.Unmarshal(b, &aux)
  36. 	if err != nil {
  37. 		return err
  38. 	}
  40. 	switch g.Type {
  41. 	case "Point":
  42. 		err = json.Unmarshal(g.Coordinates, &g.Point.Coordinates)
  43. 	case "LineString":
  44. 		err = json.Unmarshal(g.Coordinates, &g.Line.Points)
  45. 	case "Polygon":
  46. 		err = json.Unmarshal(g.Coordinates, &g.Polygon.Lines)
  47. 	}
  49. 	g.Coordinates = []byte(nil)
  51. 	return err
  52. }
  54. func (g Geojson) MarshalJSON() ([]byte, error) {
  56. 	var raw json.RawMessage
  57. 	var err error
  59. 	switch g.Type {
  60. 	case "Point":
  61. 		raw, err = json.Marshal(&g.Point.Coordinates)
  62. 	case "LineString":
  63. 		raw, err = json.Marshal(&g.Line.Points)
  64. 	case "Polygon":
  65. 		raw, err = json.Marshal(&g.Polygon.Lines)
  66. 	}
  68. 	if err != nil {
  69. 		return nil, err
  70. 	}
  72. 	g.Coordinates = raw
  74. 	type Alias Geojson
  75. 	aux := (*Alias)(&g)
  76. 	return json.Marshal(aux)
  77. }

答案3

得分: 0

根据Madu Alikor的答案，为我的用例完成了它。

  1. package geojson
  3. import (
  4. 	"encoding/json"
  5. )
  7. type PointCoordinates []float64              // 点
  8. type LineCoordinates [][]float64             // 1. 多点，2. 线
  9. type PolygonCoordinates [][][]float64        // 1. 多线，2. 多边形
  10. type MultiPolygonCoordinates [][][][]float64 // 1. 多多边形
  12. type Point struct {
  13. 	PointCoords PointCoordinates
  14. }
  16. type MultiPoint struct {
  17. 	MultiPointCoords LineCoordinates
  18. }
  20. type Line struct {
  21. 	LineCoords LineCoordinates
  22. }
  24. type MultiLine struct {
  25. 	MultiLineCoords PolygonCoordinates
  26. }
  28. type Polygon struct {
  29. 	PolygonCoords PolygonCoordinates
  30. }
  32. type MultiPolygon struct {
  33. 	MultiPolygonCoords MultiPolygonCoordinates
  34. }
  36. type Geojson struct {
  37. 	Type         string          `json:"type"`
  38. 	Coordinates  json.RawMessage `json:"coordinates"`
  39. 	Point        Point           `json:"-"`
  40. 	MultiPoint   MultiPoint      `json:"-"`
  41. 	Line         Line            `json:"-"`
  42. 	MultiLine    MultiLine       `json:"-"`
  43. 	Polygon      Polygon         `json:"-"`
  44. 	MultiPolygon MultiPolygon    `json:"-"`
  45. }
  47. func (g *Geojson) UnmarshalJSON(b []byte) error {
  49. 	type Alias Geojson
  50. 	aux := (*Alias)(g)
  52. 	err := json.Unmarshal(b, &aux)
  54. 	if err != nil {
  55. 		return err
  56. 	}
  58. 	switch g.Type {
  59. 	case "Point":
  60. 		err = json.Unmarshal(g.Coordinates, &g.Point.PointCoords)
  61. 	case "MultiPoint":
  62. 		err = json.Unmarshal(g.Coordinates, &g.MultiPoint.MultiPointCoords)
  63. 	case "LineString":
  64. 		err = json.Unmarshal(g.Coordinates, &g.Line.LineCoords)
  65. 	case "MultiLineString":
  66. 		err = json.Unmarshal(g.Coordinates, &g.MultiLine.MultiLineCoords)
  67. 	case "Polygon":
  68. 		err = json.Unmarshal(g.Coordinates, &g.Polygon.PolygonCoords)
  69. 	case "MultiPolygon":
  70. 		err = json.Unmarshal(g.Coordinates, &g.MultiPolygon.MultiPolygonCoords)
  71. 	}
  73. 	g.Coordinates = []byte(nil)
  75. 	return err
  76. }
  78. func (g Geojson) MarshalJSON() ([]byte, error) {
  80. 	var raw json.RawMessage
  81. 	var err error
  83. 	switch g.Type {
  84. 	case "Point":
  85. 		raw, err = json.Marshal(&g.Point.PointCoords)
  86. 	case "MultiPoint":
  87. 		raw, err = json.Marshal(&g.MultiPoint.MultiPointCoords)
  88. 	case "LineString":
  89. 		raw, err = json.Marshal(&g.Line.LineCoords)
  90. 	case "MultiLineString":
  91. 		raw, err = json.Marshal(&g.MultiLine.MultiLineCoords)
  92. 	case "Polygon":
  93. 		raw, err = json.Marshal(&g.Polygon.PolygonCoords)
  94. 	case "MultiPolygon":
  95. 		raw, err = json.Marshal(&g.MultiPolygon.MultiPolygonCoords)
  96. 	}
  98. 	if err != nil {
  99. 		return nil, err
  100. 	}
  102. 	g.Coordinates = raw
  104. 	type Alias Geojson
  105. 	aux := (*Alias)(&g)
  106. 	return json.Marshal(aux)
  107. }
英文:

Based on Madu Alikor answer, completed it for my use case.

  1. package geojson
  2. import (
  3. "encoding/json"
  4. )
  5. type PointCoordinates []float64              // Point
  6. type LineCoordinates [][]float64             // 1. Multipoint, 2. LineString
  7. type PolygonCoordinates [][][]float64        // 1. MultiLineString, 2. Polygon
  8. type MultiPolygonCoordinates [][][][]float64 // 1. Multi Polygon
  9. type Point struct {
  10. PointCoords PointCoordinates
  11. }
  12. type MultiPoint struct {
  13. MultiPointCoords LineCoordinates
  14. }
  15. type Line struct {
  16. LineCoords LineCoordinates
  17. }
  18. type MultiLine struct {
  19. MultiLineCoords PolygonCoordinates
  20. }
  21. type Polygon struct {
  22. PolygonCoords PolygonCoordinates
  23. }
  24. type MultiPolygon struct {
  25. MultiPolygonCoords MultiPolygonCoordinates
  26. }
  27. type Geojson struct {
  28. Type         string          `json:"type"`
  29. Coordinates  json.RawMessage `json:"coordinates"`
  30. Point        Point           `json:"-"`
  31. MultiPoint   MultiPoint      `json:"-"`
  32. Line         Line            `json:"-"`
  33. MultiLine    MultiLine       `json:"-"`
  34. Polygon      Polygon         `json:"-"`
  35. MultiPolygon MultiPolygon    `json:"-"`
  36. }
  37. func (g *Geojson) UnmarshalJSON(b []byte) error {
  38. type Alias Geojson
  39. aux := (*Alias)(g)
  40. err := json.Unmarshal(b, &aux)
  41. if err != nil {
  42. return err
  43. }
  44. switch g.Type {
  45. case "Point":
  46. err = json.Unmarshal(g.Coordinates, &g.Point.PointCoords)
  47. case "MultiPoint":
  48. err = json.Unmarshal(g.Coordinates, &g.MultiPoint.MultiPointCoords)
  49. case "LineString":
  50. err = json.Unmarshal(g.Coordinates, &g.Line.LineCoords)
  51. case "MultiLineString":
  52. err = json.Unmarshal(g.Coordinates, &g.MultiLine.MultiLineCoords)
  53. case "Polygon":
  54. err = json.Unmarshal(g.Coordinates, &g.Polygon.PolygonCoords)
  55. case "MultiPolygon":
  56. err = json.Unmarshal(g.Coordinates, &g.MultiPolygon.MultiPolygonCoords)
  57. }
  58. g.Coordinates = []byte(nil)
  59. return err
  60. }
  61. func (g Geojson) MarshalJSON() ([]byte, error) {
  62. var raw json.RawMessage
  63. var err error
  64. switch g.Type {
  65. case "Point":
  66. raw, err = json.Marshal(&g.Point.PointCoords)
  67. case "MultiPoint":
  68. raw, err = json.Marshal(&g.MultiPoint.MultiPointCoords)
  69. case "LineString":
  70. raw, err = json.Marshal(&g.Line.LineCoords)
  71. case "MultiLineString":
  72. raw, err = json.Marshal(&g.MultiLine.MultiLineCoords)
  73. case "Polygon":
  74. raw, err = json.Marshal(&g.Polygon.PolygonCoords)
  75. case "MultiPolygon":
  76. raw, err = json.Marshal(&g.MultiPolygon.MultiPolygonCoords)
  77. }
  78. if err != nil {
  79. return nil, err
  80. }
  81. g.Coordinates = raw
  82. type Alias Geojson
  83. aux := (*Alias)(&g)
  84. return json.Marshal(aux)
  85. }

huangapple
  • 本文由 发表于 2013年3月30日 22:20:34
  • 转载请务必保留本文链接：https://go.coder-hub.com/15719532.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