Converting map to struct

I am trying to create a generic method in Go that will fill a struct using data from a map[string]interface{} . For example, the method signature and usage might look like:

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

I know this can be done using JSON as an intermediary; is there another more efficient way of doing this?

1 Like

The simplest way would be to use https://github.com/mitchellh/mapstructure

import "github.com/mitchellh/mapstructure"

mapstructure.Decode(myData, &result)

If you want to do it yourself, you could do something like this:

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)