将映射转换为结构

Question

我正在尝试在 Go 中创建一个通用方法，该方法将使用来自 map[string]interface{} 的数据填充 struct。例如，方法签名和用法可能如下所示：

func FillStruct(data map[string]interface{}, result interface{}) {
    ...
}

type MyStruct struct {
    Name string
    Age  int64
}

myData := make(map[string]interface{})
myData["Name"] = "Tony"
myData["Age"]  = 23

result := &MyStruct{}
FillStruct(myData, result)

// result now has Name set to "Tony" and Age set to 23

我知道这可以使用 JSON 作为中介来完成；还有其他更有效的方法吗？

Answer 1

最简单的方法是使用https://github.com/mitchellh/mapstructure

import "github.com/mitchellh/mapstructure"

mapstructure.Decode(myData, &result)

如果你想自己做，你可以这样做：

http://play.golang.org/p/tN8mxT_V9h

func SetField(obj interface{}, name string, value interface{}) error {
    structValue := reflect.ValueOf(obj).Elem()
    structFieldValue := structValue.FieldByName(name)

    if !structFieldValue.IsValid() {
        return fmt.Errorf("No such field: %s in obj", name)
    }

    if !structFieldValue.CanSet() {
        return fmt.Errorf("Cannot set %s field value", name)
    }

    structFieldType := structFieldValue.Type()
    val := reflect.ValueOf(value)
    if structFieldType != val.Type() {
        return errors.New("Provided value type didn't match obj field type")
    }

    structFieldValue.Set(val)
    return nil
}

type MyStruct struct {
    Name string
    Age  int64
}

func (s *MyStruct) FillStruct(m map[string]interface{}) error {
    for k, v := range m {
        err := SetField(s, k, v)
        if err != nil {
            return err
        }
    }
    return nil
}

func main() {
    myData := make(map[string]interface{})
    myData["Name"] = "Tony"
    myData["Age"] = int64(23)

    result := &MyStruct{}
    err := result.FillStruct(myData)
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(result)
}

Answer 2

Hashicorp 的 https://github.com/mitchellh/mapstructure 库开箱即用：

import "github.com/mitchellh/mapstructure"

mapstructure.Decode(myData, &result)

第二个result 参数必须是结构的地址。

Answer 3

• 最简单的方法是使用encoding/json 包

举例：

package main
import (
    "fmt"
    "encoding/json"
)

type MyAddress struct {
    House string
    School string
}
type Student struct {
    Id int64
    Name string
    Scores float32
    Address MyAddress
    Labels []string
}

func Test() {

    dict := make(map[string]interface{})
    dict["id"] = 201902181425       // int
    dict["name"] = "jackytse"       // string
    dict["scores"] = 123.456        // float
    dict["address"] = map[string]string{"house":"my house", "school":"my school"}   // map
    dict["labels"] = []string{"aries", "warmhearted", "frank"}      // slice

    jsonbody, err := json.Marshal(dict)
    if err != nil {
        // do error check
        fmt.Println(err)
        return
    }

    student := Student{}
    if err := json.Unmarshal(jsonbody, &student); err != nil {
        // do error check
        fmt.Println(err)
        return
    }

    fmt.Printf("%#v\n", student)
}

func main() {
    Test()
}

Answer 4

你可以做到......它可能会有点难看，你会在映射类型方面面临一些试验和错误......但这是它的基本要点：

func FillStruct(data map[string]interface{}, result interface{}) {
    t := reflect.ValueOf(result).Elem()
    for k, v := range data {
        val := t.FieldByName(k)
        val.Set(reflect.ValueOf(v))
    }
}

工作样本：http://play.golang.org/p/PYHz63sbvL

Answer 5

有两个步骤：

1. 将接口转换为 JSON 字节
2. 将 JSON 字节转换为结构

下面是一个例子：

dbByte, _ := json.Marshal(dbContent)
_ = json.Unmarshal(dbByte, &MyStruct)

Answer 6

您可以通过 JSON 进行往返：

package main

import (
   "bytes"
   "encoding/json"
)

func transcode(in, out interface{}) {
   buf := new(bytes.Buffer)
   json.NewEncoder(buf).Encode(in)
   json.NewDecoder(buf).Decode(out)
}

例子：

package main
import "fmt"

type myStruct struct {
   Name string
   Age  int64
}

func main() {
   myData := map[string]interface{}{
      "Name": "Tony",
      "Age": 23,
   }
   var result myStruct
   transcode(myData, &result)
   fmt.Printf("%+v\n", result) // {Name:Tony Age:23}
}

Answer 7

我改编了戴夫的回答，并添加了递归功能。我仍在开发更用户友好的版本。例如，map 中的数字字符串应该可以在 struct 中转换为 int。

package main

import (
    "fmt"
    "reflect"
)

func SetField(obj interface{}, name string, value interface{}) error {

    structValue := reflect.ValueOf(obj).Elem()
    fieldVal := structValue.FieldByName(name)

    if !fieldVal.IsValid() {
        return fmt.Errorf("No such field: %s in obj", name)
    }

    if !fieldVal.CanSet() {
        return fmt.Errorf("Cannot set %s field value", name)
    }

    val := reflect.ValueOf(value)

    if fieldVal.Type() != val.Type() {

        if m,ok := value.(map[string]interface{}); ok {

            // if field value is struct
            if fieldVal.Kind() == reflect.Struct {
                return FillStruct(m, fieldVal.Addr().Interface())
            }

            // if field value is a pointer to struct
            if fieldVal.Kind()==reflect.Ptr && fieldVal.Type().Elem().Kind() == reflect.Struct {
                if fieldVal.IsNil() {
                    fieldVal.Set(reflect.New(fieldVal.Type().Elem()))
                }
                // fmt.Printf("recursive: %v %v\n", m,fieldVal.Interface())
                return FillStruct(m, fieldVal.Interface())
            }

        }

        return fmt.Errorf("Provided value type didn't match obj field type")
    }

    fieldVal.Set(val)
    return nil

}

func FillStruct(m map[string]interface{}, s interface{}) error {
    for k, v := range m {
        err := SetField(s, k, v)
        if err != nil {
            return err
        }
    }
    return nil
}

type OtherStruct struct {
    Name string
    Age  int64
}


type MyStruct struct {
    Name string
    Age  int64
    OtherStruct *OtherStruct
}



func main() {
    myData := make(map[string]interface{})
    myData["Name"]        = "Tony"
    myData["Age"]         = int64(23)
    OtherStruct := make(map[string]interface{})
    myData["OtherStruct"] = OtherStruct
    OtherStruct["Name"]   = "roxma"
    OtherStruct["Age"]    = int64(23)

    result := &MyStruct{}
    err := FillStruct(myData,result)
    fmt.Println(err)
    fmt.Printf("%v %v\n",result,result.OtherStruct)
}