使用Go反射进行复杂对象的反序列化方法

huangapple
go评论120阅读模式
英文:

Unmarshal method for complex object with go reflections

问题

我正在开始编写更复杂的Go代码，我的目标是将JSON对象的列表转换为具有特定键的映射。这个操作可以帮助我加快算法的速度。但是我现在遇到了一个问题，我的容器结构体中有几个复杂的JSON字段，我无法编写一个通用的解决方案来实现这个操作。我目前想到的唯一方法是使用一个大的switch case语句，但我认为这不是正确的解决方案。

以下是我目前的代码，其中statusChannel在代码中是一个映射，但在JSON字符串中是一个列表：

  1. type MetricOne struct {
  2. 	// Internal id to identify the metric
  3. 	id int `json:"-"`
  4. 	// Version of metrics format, it is used to migrate the
  5. 	// JSON payload from previous version of plugin.
  6. 	Version int `json:"version"`
  7. 	// Name of the metrics
  8. 	Name   string  `json:"metric_name"`
  9. 	NodeId string  `json:"node_id"`
  10. 	Color  string  `json:"color"`
  11. 	OSInfo *osInfo `json:"os_info"`
  12. 	// timezone where the node is located
  13. 	Timezone string `json:"timezone"`
  14. 	// array of the up_time
  15. 	UpTime []*status `json:"up_time"`
  16. 	// map of informatonof channel information
  17. 	ChannelsInfo map[string]*statusChannel `json:"channels_info"`
  18. }
  20. func (instance *MetricOne) MarshalJSON() ([]byte, error) {
  21. 	jsonMap := make(map[string]interface{})
  22. 	reflectType := reflect.TypeOf(*instance)
  23. 	reflectValue := reflect.ValueOf(*instance)
  24. 	nFiled := reflectValue.Type().NumField()
  26. 	for i := 0; i < nFiled; i++ {
  27. 		key := reflectType.Field(i)
  28. 		valueFiled := reflectValue.Field(i)
  29. 		jsonName := key.Tag.Get("json")
  30. 		switch jsonName {
  31. 		case "-":
  32. 			// skip
  33. 			continue
  34. 		case "channels_info":
  35. 			// TODO convert the map[string]*statusChannel in a list of statusChannel
  36. 			statusChannels := make([]*statusChannel, 0)
  37. 			for _, value := range valueFiled.Interface().(map[string]*statusChannel) {
  38. 				statusChannels = append(statusChannels, value)
  39. 			}
  40. 			jsonMap[jsonName] = statusChannels
  41. 		default:
  42. 			jsonMap[jsonName] = valueFiled.Interface()
  43. 		}
  44. 	}
  46. 	return json.Marshal(jsonMap)
  47. }
  49. func (instance *MetricOne) UnmarshalJSON(data []byte) error {
  50. 	var jsonMap map[string]interface{}
  51. 	err := json.Unmarshal(data, &jsonMap)
  52. 	if err != nil {
  53. 		log.GetInstance().Error(fmt.Sprintf("Error: %s", err))
  54. 		return err
  55. 	}
  56. 	instance.Migrate(jsonMap)
  57. 	reflectValue := reflect.ValueOf(instance)
  58. 	reflectStruct := reflectValue.Elem()
  59. 	// reflectType := reflectValue.Type()
  60. 	for key, value := range jsonMap {
  61. 		fieldName, err := utils.GetFieldName(key, "json", *instance)
  62. 		if err != nil {
  63. 			log.GetInstance().Info(fmt.Sprintf("Error: %s", err))
  64. 			if strings.Contains(key, "dev_") {
  65. 				log.GetInstance().Info("dev propriety skipped if missed")
  66. 				continue
  67. 			}
  68. 			return err
  69. 		}
  70. 		field := reflectStruct.FieldByName(*fieldName)
  71. 		fieldType := field.Type()
  72. 		filedValue := field.Interface()
  73. 		val := reflect.ValueOf(filedValue)
  75. 		switch key {
  76. 		case "channels_info":
  77. 			statusChannelsMap := make(map[string]*statusChannel)
  78. 			toArray := value.([]interface{})
  79. 			for _, status := range toArray {
  80. 				var statusType statusChannel
  81. 				jsonVal, err := json.Marshal(status)
  82. 				if err != nil {
  83. 					return err
  84. 				}
  85. 				err = json.Unmarshal(jsonVal, &statusType)
  86. 				if err != nil {
  87. 					return err
  88. 				}
  89. 				statusChannelsMap[statusType.ChannelId] = &statusType
  90. 			}
  91. 			field.Set(reflect.ValueOf(statusChannelsMap))
  92. 		default:
  93. 			field.Set(val.Convert(fieldType))
  94. 		}
  95. 	}
  96. 	return nil
  97. }

当我解码对象时，我收到以下错误：

  1. panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo [recovered]
  2. panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo

有人能解释一下如何以通用的方式执行此操作吗？

英文:

I'm starting to writing more complex go code, and my object node it to convert a list from a JSON object to a map with a particular key. This operation helps me to speed up my algorithm. But I have a problem now, my container struct has several complex JSON and I'm not able to write a generic solution to achieve a generic solution. The only way that I have in mind is to use a big switch case, but I think this is not the right solution.

This is my code at the moment, where the statusChannel is a map in the code but it is a list in the JSON string

  1. type MetricOne struct {
  2. // Internal id to identify the metric
  3. id int `json:&quot;-&quot;`
  4. // Version of metrics format, it is used to migrate the
  5. // JSON payload from previous version of plugin.
  6. Version int `json:&quot;version&quot;`
  7. // Name of the metrics
  8. Name   string  `json:&quot;metric_name&quot;`
  9. NodeId string  `json:&quot;node_id&quot;`
  10. Color  string  `json:&quot;color&quot;`
  11. OSInfo *osInfo `json:&quot;os_info&quot;`
  12. // timezone where the node is located
  13. Timezone string `json:&quot;timezone&quot;`
  14. // array of the up_time
  15. UpTime []*status `json:&quot;up_time&quot;`
  16. // map of informatonof channel information
  17. ChannelsInfo map[string]*statusChannel `json:&quot;channels_info&quot;`
  18. }
  19. func (instance *MetricOne) MarshalJSON() ([]byte, error) {
  20. jsonMap := make(map[string]interface{})
  21. reflectType := reflect.TypeOf(*instance)
  22. reflectValue := reflect.ValueOf(*instance)
  23. nFiled := reflectValue.Type().NumField()
  24. for i := 0; i &lt; nFiled; i++ {
  25. key := reflectType.Field(i)
  26. valueFiled := reflectValue.Field(i)
  27. jsonName := key.Tag.Get(&quot;json&quot;)
  28. switch jsonName {
  29. case &quot;-&quot;:
  30. // skip
  31. continue
  32. case &quot;channels_info&quot;:
  33. // TODO convert the map[string]*statusChannel in a list of statusChannel
  34. statusChannels := make([]*statusChannel, 0)
  35. for _, value := range valueFiled.Interface().(map[string]*statusChannel) {
  36. statusChannels = append(statusChannels, value)
  37. }
  38. jsonMap[jsonName] = statusChannels
  39. default:
  40. jsonMap[jsonName] = valueFiled.Interface()
  41. }
  42. }
  43. return json.Marshal(jsonMap)
  44. }
  45. func (instance *MetricOne) UnmarshalJSON(data []byte) error {
  46. var jsonMap map[string]interface{}
  47. err := json.Unmarshal(data, &amp;jsonMap)
  48. if err != nil {
  49. log.GetInstance().Error(fmt.Sprintf(&quot;Error: %s&quot;, err))
  50. return err
  51. }
  52. instance.Migrate(jsonMap)
  53. reflectValue := reflect.ValueOf(instance)
  54. reflectStruct := reflectValue.Elem()
  55. // reflectType := reflectValue.Type()
  56. for key, value := range jsonMap {
  57. fieldName, err := utils.GetFieldName(key, &quot;json&quot;, *instance)
  58. if err != nil {
  59. log.GetInstance().Info(fmt.Sprintf(&quot;Error: %s&quot;, err))
  60. if strings.Contains(key, &quot;dev_&quot;) {
  61. log.GetInstance().Info(&quot;dev propriety skipped if missed&quot;)
  62. continue
  63. }
  64. return err
  65. }
  66. field := reflectStruct.FieldByName(*fieldName)
  67. fieldType := field.Type()
  68. filedValue := field.Interface()
  69. val := reflect.ValueOf(filedValue)
  70. switch key {
  71. case &quot;channels_info&quot;:
  72. statusChannelsMap := make(map[string]*statusChannel)
  73. toArray := value.([]interface{})
  74. for _, status := range toArray {
  75. var statusType statusChannel
  76. jsonVal, err := json.Marshal(status)
  77. if err != nil {
  78. return err
  79. }
  80. err = json.Unmarshal(jsonVal, &amp;statusType)
  81. if err != nil {
  82. return err
  83. }
  84. statusChannelsMap[statusType.ChannelId] = &amp;statusType
  85. }
  86. field.Set(reflect.ValueOf(statusChannelsMap))
  87. default:
  88. field.Set(val.Convert(fieldType))
  89. }
  90. }
  91. return nil
  92. }

And when I will decode the object I receive the following error:

  1. ➜  go-metrics-reported git:(dev) ✗ make check
  2. go test -v ./...
  3. ?   	github.com/OpenLNMetrics/go-metrics-reported/cmd/go-metrics-reported	[no test files]
  4. ?   	github.com/OpenLNMetrics/go-metrics-reported/init/persistence	[no test files]
  5. === RUN   TestJSONSerializzation
  6. --- PASS: TestJSONSerializzation (0.00s)
  7. === RUN   TestJSONDeserializzation
  8. --- FAIL: TestJSONDeserializzation (0.00s)
  9. panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo [recovered]
  10. panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo
  11. goroutine 7 [running]:
  12. testing.tRunner.func1.1(0x61b440, 0xc0001d69a0)
  13. /home/vincent/.gosdk/go/src/testing/testing.go:1072 +0x30d
  14. testing.tRunner.func1(0xc000001e00)
  15. /home/vincent/.gosdk/go/src/testing/testing.go:1075 +0x41a
  16. panic(0x61b440, 0xc0001d69a0)
  17. /home/vincent/.gosdk/go/src/runtime/panic.go:969 +0x1b9
  18. reflect.Value.Convert(0x6283e0, 0xc0001bb1a0, 0x15, 0x6b93a0, 0x610dc0, 0x610dc0, 0xc00014cb40, 0x196)
  19. /home/vincent/.gosdk/go/src/reflect/value.go:2447 +0x229
  20. github.com/OpenLNMetrics/go-metrics-reported/internal/plugin.(*MetricOne).UnmarshalJSON(0xc00014cb00, 0xc0001d8000, 0x493, 0x500, 0x7f04d01453d8, 0xc00014cb00)
  21. /home/vincent/Github/OpenLNMetrics/go-metrics-reported/internal/plugin/metrics_one.go:204 +0x5b3
  22. encoding/json.(*decodeState).object(0xc00010be40, 0x657160, 0xc00014cb00, 0x16, 0xc00010be68, 0x7b)
  23. /home/vincent/.gosdk/go/src/encoding/json/decode.go:609 +0x207c
  24. encoding/json.(*decodeState).value(0xc00010be40, 0x657160, 0xc00014cb00, 0x16, 0xc000034698, 0x54ec19)
  25. /home/vincent/.gosdk/go/src/encoding/json/decode.go:370 +0x6d
  26. encoding/json.(*decodeState).unmarshal(0xc00010be40, 0x657160, 0xc00014cb00, 0xc00010be68, 0x0)
  27. /home/vincent/.gosdk/go/src/encoding/json/decode.go:180 +0x1ea
  28. encoding/json.Unmarshal(0xc0001d8000, 0x493, 0x500, 0x657160, 0xc00014cb00, 0x500, 0x48cba6)
  29. /home/vincent/.gosdk/go/src/encoding/json/decode.go:107 +0x112
  30. github.com/OpenLNMetrics/go-metrics-reported/internal/plugin.TestJSONDeserializzation(0xc000001e00)
  31. /home/vincent/Github/OpenLNMetrics/go-metrics-reported/internal/plugin/metric_one_test.go:87 +0x95
  32. testing.tRunner(0xc000001e00, 0x681000)
  33. /home/vincent/.gosdk/go/src/testing/testing.go:1123 +0xef
  34. created by testing.(*T).Run
  35. /home/vincent/.gosdk/go/src/testing/testing.go:1168 +0x2b3
  36. FAIL	github.com/OpenLNMetrics/go-metrics-reported/internal/plugin	0.008s
  37. ?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/db	[no test files]
  38. ?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/graphql	[no test files]
  39. ?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/log	[no test files]
  40. ?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/utils	[no test files]
  41. FAIL
  42. make: *** [Makefile:15: check] Error 1

can someone explain how I can do this operation in a generic way?

答案1

得分: 3

  1. type MetricOne struct {
  2.     // ...
  4.     // 忽略该字段。
  5. 	ChannelsInfo map[string]*statusChannel `json:"-"`
  6. }
  1. func (m MetricOne) MarshalJSON() ([]byte, error) {
  2.     // 声明一个新类型，使用MetricOne的定义，
  3.     // 这样M将具有与MetricOne相同的结构，
  4.     // 但没有它的方法（这避免了对MarshalJSON的递归调用）。
  5.     //
  6.     // 由于M和MetricOne具有相同的结构，你可以轻松地在这两者之间进行转换。
  7.     // 例如，M(MetricOne{})和MetricOne(M{})都是有效的表达式。
  8. 	type M MetricOne
  10.     // 声明一个新类型，该类型具有“desired”类型的字段，
  11.     // 并且还**嵌入**了M类型。嵌入将M的字段提升为T，
  12.     // 并且encoding/json将对这些字段进行扁平化编组，
  13.     // 即与channels_info字段处于同一级别。
  14. 	type T struct {
  15. 		M
  16. 		ChannelsInfo []*statusChannel `json:"channels_info"`
  17. 	}
  19.     // 将map元素移动到slice中
  20. 	channels := make([]*statusChannel, 0, len(m.ChannelsInfo))
  21. 	for _, c := range m.ChannelsInfo {
  22. 		channels = append(channels, c)
  23. 	}
  25.     // 将新类型T的实例传递给json.Marshal。
  26.     // 对于嵌入的M字段，使用接收器的转换实例。
  27.     // 对于ChannelsInfo字段，使用channels切片。
  28. 	return json.Marshal(T{
  29.         M:            M(m),
  30.         ChannelsInfo: channels,
  31.     })
  32. }
  1. // 与MarshalJSON相同，但是反向操作。
  2. func (m *MetricOne) UnmarshalJSON(data []byte) error {
  3. 	type M MetricOne
  4. 	type T struct {
  5. 		*M
  6. 		ChannelsInfo []*statusChannel `json:"channels_info"`
  7. 	}
  8. 	t := T{M: (*M)(m)}
  9. 	if err := json.Unmarshal(data, &t); err != nil {
  10. 		panic(err)
  11. 	}
  13. 	m.ChannelsInfo = make(map[string]*statusChannel, len(t.ChannelsInfo))
  14. 	for _, c := range t.ChannelsInfo {
  15. 		m.ChannelsInfo[c.ChannelId] = c
  16. 	}
  18. 	return nil
  19. }
英文:

https://play.golang.org/p/jzU_lHj1wk7

  1. type MetricOne struct {
  2.     // ...
  4.     // Have this field be ignored.
  5. 	ChannelsInfo map[string]*statusChannel `json:&quot;-&quot;`
  6. }
  1. func (m MetricOne) MarshalJSON() ([]byte, error) {
  2.     // Declare a new type using the definition of MetricOne,
  3.     // the result of this is that M will have the same structure
  4.     // as MetricOne but none of its methods (this avoids recursive
  5.     // calls to MarshalJSON).
  6.     //
  7.     // Also because M and MetricOne have the same structure you can
  8.     // easily convert between those two. e.g. M(MetricOne{}) and
  9.     // MetricOne(M{}) are valid expressions.
  10. 	type M MetricOne
  12.     // Declare a new type that has a field of the &quot;desired&quot; type and
  13.     // also **embeds** the M type. Embedding promotes M&#39;s fields to T
  14.     // and encoding/json will marshal those fields unnested/flattened, 
  15.     // i.e. at the same level as the channels_info field.
  16. 	type T struct {
  17. 		M
  18. 		ChannelsInfo []*statusChannel `json:&quot;channels_info&quot;`
  19. 	}
  21.     // move map elements to slice
  22. 	channels := make([]*statusChannel, 0, len(m.ChannelsInfo))
  23. 	for _, c := range m.ChannelsInfo {
  24. 		channels = append(channels, c)
  25. 	}
  27.     // Pass in an instance of the new type T to json.Marshal.
  28.     // For the embedded M field use a converted instance of the receiver.
  29.     // For the ChannelsInfo field use the channels slice.
  30. 	return json.Marshal(T{
  31.         M:            M(m),
  32.         ChannelsInfo: channels,
  33.     })
  34. }
  1. // Same as MarshalJSON but in reverse.
  2. func (m *MetricOne) UnmarshalJSON(data []byte) error {
  3. 	type M MetricOne
  4. 	type T struct {
  5. 		*M
  6. 		ChannelsInfo []*statusChannel `json:&quot;channels_info&quot;`
  7. 	}
  8. 	t := T{M: (*M)(m)}
  9. 	if err := json.Unmarshal(data, &amp;t); err != nil {
  10. 		panic(err)
  11. 	}
  13. 	m.ChannelsInfo = make(map[string]*statusChannel, len(t.ChannelsInfo))
  14. 	for _, c := range t.ChannelsInfo {
  15. 		m.ChannelsInfo[c.ChannelId] = c
  16. 	}
  18. 	return nil
  19. }

huangapple
  • 本文由 发表于 2021年8月18日 20:52:42
  • 转载请务必保留本文链接：https://go.coder-hub.com/68832776.html
  • go
  • reflection
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