使用Go反射进行复杂对象的反序列化方法

huangapple
go评论84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：

type MetricOne struct {
	// Internal id to identify the metric
	id int `json:"-"`
	// Version of metrics format, it is used to migrate the
	// JSON payload from previous version of plugin.
	Version int `json:"version"`
	// Name of the metrics
	Name   string  `json:"metric_name"`
	NodeId string  `json:"node_id"`
	Color  string  `json:"color"`
	OSInfo *osInfo `json:"os_info"`
	// timezone where the node is located
	Timezone string `json:"timezone"`
	// array of the up_time
	UpTime []*status `json:"up_time"`
	// map of informatonof channel information
	ChannelsInfo map[string]*statusChannel `json:"channels_info"`
}

func (instance *MetricOne) MarshalJSON() ([]byte, error) {
	jsonMap := make(map[string]interface{})
	reflectType := reflect.TypeOf(*instance)
	reflectValue := reflect.ValueOf(*instance)
	nFiled := reflectValue.Type().NumField()

	for i := 0; i < nFiled; i++ {
		key := reflectType.Field(i)
		valueFiled := reflectValue.Field(i)
		jsonName := key.Tag.Get("json")
		switch jsonName {
		case "-":
			// skip
			continue
		case "channels_info":
			// TODO convert the map[string]*statusChannel in a list of statusChannel
			statusChannels := make([]*statusChannel, 0)
			for _, value := range valueFiled.Interface().(map[string]*statusChannel) {
				statusChannels = append(statusChannels, value)
			}
			jsonMap[jsonName] = statusChannels
		default:
			jsonMap[jsonName] = valueFiled.Interface()
		}
	}

	return json.Marshal(jsonMap)
}

func (instance *MetricOne) UnmarshalJSON(data []byte) error {
	var jsonMap map[string]interface{}
	err := json.Unmarshal(data, &jsonMap)
	if err != nil {
		log.GetInstance().Error(fmt.Sprintf("Error: %s", err))
		return err
	}
	instance.Migrate(jsonMap)
	reflectValue := reflect.ValueOf(instance)
	reflectStruct := reflectValue.Elem()
	// reflectType := reflectValue.Type()
	for key, value := range jsonMap {
		fieldName, err := utils.GetFieldName(key, "json", *instance)
		if err != nil {
			log.GetInstance().Info(fmt.Sprintf("Error: %s", err))
			if strings.Contains(key, "dev_") {
				log.GetInstance().Info("dev propriety skipped if missed")
				continue
			}
			return err
		}
		field := reflectStruct.FieldByName(*fieldName)
		fieldType := field.Type()
		filedValue := field.Interface()
		val := reflect.ValueOf(filedValue)

		switch key {
		case "channels_info":
			statusChannelsMap := make(map[string]*statusChannel)
			toArray := value.([]interface{})
			for _, status := range toArray {
				var statusType statusChannel
				jsonVal, err := json.Marshal(status)
				if err != nil {
					return err
				}
				err = json.Unmarshal(jsonVal, &statusType)
				if err != nil {
					return err
				}
				statusChannelsMap[statusType.ChannelId] = &statusType
			}
			field.Set(reflect.ValueOf(statusChannelsMap))
		default:
			field.Set(val.Convert(fieldType))
		}
	}
	return nil
}

当我解码对象时，我收到以下错误：

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

type MetricOne struct {
// Internal id to identify the metric
id int `json:&quot;-&quot;`
// Version of metrics format, it is used to migrate the
// JSON payload from previous version of plugin.
Version int `json:&quot;version&quot;`
// Name of the metrics
Name   string  `json:&quot;metric_name&quot;`
NodeId string  `json:&quot;node_id&quot;`
Color  string  `json:&quot;color&quot;`
OSInfo *osInfo `json:&quot;os_info&quot;`
// timezone where the node is located
Timezone string `json:&quot;timezone&quot;`
// array of the up_time
UpTime []*status `json:&quot;up_time&quot;`
// map of informatonof channel information
ChannelsInfo map[string]*statusChannel `json:&quot;channels_info&quot;`
}
func (instance *MetricOne) MarshalJSON() ([]byte, error) {
jsonMap := make(map[string]interface{})
reflectType := reflect.TypeOf(*instance)
reflectValue := reflect.ValueOf(*instance)
nFiled := reflectValue.Type().NumField()
for i := 0; i &lt; nFiled; i++ {
key := reflectType.Field(i)
valueFiled := reflectValue.Field(i)
jsonName := key.Tag.Get(&quot;json&quot;)
switch jsonName {
case &quot;-&quot;:
// skip
continue
case &quot;channels_info&quot;:
// TODO convert the map[string]*statusChannel in a list of statusChannel
statusChannels := make([]*statusChannel, 0)
for _, value := range valueFiled.Interface().(map[string]*statusChannel) {
statusChannels = append(statusChannels, value)
}
jsonMap[jsonName] = statusChannels
default:
jsonMap[jsonName] = valueFiled.Interface()
}
}
return json.Marshal(jsonMap)
}
func (instance *MetricOne) UnmarshalJSON(data []byte) error {
var jsonMap map[string]interface{}
err := json.Unmarshal(data, &amp;jsonMap)
if err != nil {
log.GetInstance().Error(fmt.Sprintf(&quot;Error: %s&quot;, err))
return err
}
instance.Migrate(jsonMap)
reflectValue := reflect.ValueOf(instance)
reflectStruct := reflectValue.Elem()
// reflectType := reflectValue.Type()
for key, value := range jsonMap {
fieldName, err := utils.GetFieldName(key, &quot;json&quot;, *instance)
if err != nil {
log.GetInstance().Info(fmt.Sprintf(&quot;Error: %s&quot;, err))
if strings.Contains(key, &quot;dev_&quot;) {
log.GetInstance().Info(&quot;dev propriety skipped if missed&quot;)
continue
}
return err
}
field := reflectStruct.FieldByName(*fieldName)
fieldType := field.Type()
filedValue := field.Interface()
val := reflect.ValueOf(filedValue)
switch key {
case &quot;channels_info&quot;:
statusChannelsMap := make(map[string]*statusChannel)
toArray := value.([]interface{})
for _, status := range toArray {
var statusType statusChannel
jsonVal, err := json.Marshal(status)
if err != nil {
return err
}
err = json.Unmarshal(jsonVal, &amp;statusType)
if err != nil {
return err
}
statusChannelsMap[statusType.ChannelId] = &amp;statusType
}
field.Set(reflect.ValueOf(statusChannelsMap))
default:
field.Set(val.Convert(fieldType))
}
}
return nil
}

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

➜  go-metrics-reported git:(dev) ✗ make check
go test -v ./...
?   	github.com/OpenLNMetrics/go-metrics-reported/cmd/go-metrics-reported	[no test files]
?   	github.com/OpenLNMetrics/go-metrics-reported/init/persistence	[no test files]
=== RUN   TestJSONSerializzation
--- PASS: TestJSONSerializzation (0.00s)
=== RUN   TestJSONDeserializzation
--- FAIL: TestJSONDeserializzation (0.00s)
panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo [recovered]
panic: reflect.Value.Convert: value of type map[string]interface {} cannot be converted to type *plugin.osInfo
goroutine 7 [running]:
testing.tRunner.func1.1(0x61b440, 0xc0001d69a0)
/home/vincent/.gosdk/go/src/testing/testing.go:1072 +0x30d
testing.tRunner.func1(0xc000001e00)
/home/vincent/.gosdk/go/src/testing/testing.go:1075 +0x41a
panic(0x61b440, 0xc0001d69a0)
/home/vincent/.gosdk/go/src/runtime/panic.go:969 +0x1b9
reflect.Value.Convert(0x6283e0, 0xc0001bb1a0, 0x15, 0x6b93a0, 0x610dc0, 0x610dc0, 0xc00014cb40, 0x196)
/home/vincent/.gosdk/go/src/reflect/value.go:2447 +0x229
github.com/OpenLNMetrics/go-metrics-reported/internal/plugin.(*MetricOne).UnmarshalJSON(0xc00014cb00, 0xc0001d8000, 0x493, 0x500, 0x7f04d01453d8, 0xc00014cb00)
/home/vincent/Github/OpenLNMetrics/go-metrics-reported/internal/plugin/metrics_one.go:204 +0x5b3
encoding/json.(*decodeState).object(0xc00010be40, 0x657160, 0xc00014cb00, 0x16, 0xc00010be68, 0x7b)
/home/vincent/.gosdk/go/src/encoding/json/decode.go:609 +0x207c
encoding/json.(*decodeState).value(0xc00010be40, 0x657160, 0xc00014cb00, 0x16, 0xc000034698, 0x54ec19)
/home/vincent/.gosdk/go/src/encoding/json/decode.go:370 +0x6d
encoding/json.(*decodeState).unmarshal(0xc00010be40, 0x657160, 0xc00014cb00, 0xc00010be68, 0x0)
/home/vincent/.gosdk/go/src/encoding/json/decode.go:180 +0x1ea
encoding/json.Unmarshal(0xc0001d8000, 0x493, 0x500, 0x657160, 0xc00014cb00, 0x500, 0x48cba6)
/home/vincent/.gosdk/go/src/encoding/json/decode.go:107 +0x112
github.com/OpenLNMetrics/go-metrics-reported/internal/plugin.TestJSONDeserializzation(0xc000001e00)
/home/vincent/Github/OpenLNMetrics/go-metrics-reported/internal/plugin/metric_one_test.go:87 +0x95
testing.tRunner(0xc000001e00, 0x681000)
/home/vincent/.gosdk/go/src/testing/testing.go:1123 +0xef
created by testing.(*T).Run
/home/vincent/.gosdk/go/src/testing/testing.go:1168 +0x2b3
FAIL	github.com/OpenLNMetrics/go-metrics-reported/internal/plugin	0.008s
?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/db	[no test files]
?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/graphql	[no test files]
?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/log	[no test files]
?   	github.com/OpenLNMetrics/go-metrics-reported/pkg/utils	[no test files]
FAIL
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

type MetricOne struct {
    // ...

    // 忽略该字段。
	ChannelsInfo map[string]*statusChannel `json:"-"`
}

func (m MetricOne) MarshalJSON() ([]byte, error) {
    // 声明一个新类型，使用MetricOne的定义，
    // 这样M将具有与MetricOne相同的结构，
    // 但没有它的方法（这避免了对MarshalJSON的递归调用）。
    //
    // 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。
    // 例如，M(MetricOne{})和MetricOne(M{})都是有效的表达式。
	type M MetricOne

    // 声明一个新类型，该类型具有“desired”类型的字段，
    // 并且还**嵌入**了M类型。嵌入将M的字段提升为T，
    // 并且encoding/json将对这些字段进行扁平化编组，
    // 即与channels_info字段处于同一级别。
	type T struct {
		M
		ChannelsInfo []*statusChannel `json:"channels_info"`
	}

    // 将map元素移动到slice中
	channels := make([]*statusChannel, 0, len(m.ChannelsInfo))
	for _, c := range m.ChannelsInfo {
		channels = append(channels, c)
	}

    // 将新类型T的实例传递给json.Marshal。
    // 对于嵌入的M字段，使用接收器的转换实例。
    // 对于ChannelsInfo字段，使用channels切片。
	return json.Marshal(T{
        M:            M(m),
        ChannelsInfo: channels,
    })
}

// 与MarshalJSON相同，但是反向操作。
func (m *MetricOne) UnmarshalJSON(data []byte) error {
	type M MetricOne
	type T struct {
		*M
		ChannelsInfo []*statusChannel `json:"channels_info"`
	}
	t := T{M: (*M)(m)}
	if err := json.Unmarshal(data, &t); err != nil {
		panic(err)
	}

	m.ChannelsInfo = make(map[string]*statusChannel, len(t.ChannelsInfo))
	for _, c := range t.ChannelsInfo {
		m.ChannelsInfo[c.ChannelId] = c
	}

	return nil
}
英文:

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

type MetricOne struct {
    // ...

    // Have this field be ignored.
	ChannelsInfo map[string]*statusChannel `json:&quot;-&quot;`
}

func (m MetricOne) MarshalJSON() ([]byte, error) {
    // Declare a new type using the definition of MetricOne,
    // the result of this is that M will have the same structure
    // as MetricOne but none of its methods (this avoids recursive
    // calls to MarshalJSON).
    //
    // Also because M and MetricOne have the same structure you can
    // easily convert between those two. e.g. M(MetricOne{}) and
    // MetricOne(M{}) are valid expressions.
	type M MetricOne

    // Declare a new type that has a field of the &quot;desired&quot; type and
    // also **embeds** the M type. Embedding promotes M&#39;s fields to T
    // and encoding/json will marshal those fields unnested/flattened, 
    // i.e. at the same level as the channels_info field.
	type T struct {
		M
		ChannelsInfo []*statusChannel `json:&quot;channels_info&quot;`
	}

    // move map elements to slice
	channels := make([]*statusChannel, 0, len(m.ChannelsInfo))
	for _, c := range m.ChannelsInfo {
		channels = append(channels, c)
	}

    // Pass in an instance of the new type T to json.Marshal.
    // For the embedded M field use a converted instance of the receiver.
    // For the ChannelsInfo field use the channels slice.
	return json.Marshal(T{
        M:            M(m),
        ChannelsInfo: channels,
    })
}

// Same as MarshalJSON but in reverse.
func (m *MetricOne) UnmarshalJSON(data []byte) error {
	type M MetricOne
	type T struct {
		*M
		ChannelsInfo []*statusChannel `json:&quot;channels_info&quot;`
	}
	t := T{M: (*M)(m)}
	if err := json.Unmarshal(data, &amp;t); err != nil {
		panic(err)
	}

	m.ChannelsInfo = make(map[string]*statusChannel, len(t.ChannelsInfo))
	for _, c := range t.ChannelsInfo {
		m.ChannelsInfo[c.ChannelId] = c
	}

	return nil
}

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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