patterngoCritical
Converting map to struct
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structconvertingmap
Problem
I am trying to create a generic method in Go that will fill a
I know this can be done using JSON as an intermediary; is there another more efficient way of doing this?
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 23I know this can be done using JSON as an intermediary; is there another more efficient way of doing this?
Solution
The simplest way would be to use https://github.com/mitchellh/mapstructure
If you want to do it yourself, you could do something like this:
http://play.golang.org/p/tN8mxT_V9h
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)
}Code Snippets
import "github.com/mitchellh/mapstructure"
mapstructure.Decode(myData, &result)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)
}Context
Stack Overflow Q#26744873, score: 188
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