How to access struct with a variable? - go

Question

I'm new to Go and I'm facing issues in accessing a struct with a variable
I have this function decodeUser. My task is to check whether the keys are present in the request. So this is what I did. I've added a comment where I got the error.
func decodeUser(r *http.Request) (root.User, []string, error) {
var u root.User
if r.Body == nil {
return u, []string{}, errors.New("no request body")
}
decoder := json.NewDecoder(r.Body)
checks := []string{
"UserName",
"FirstName",
"LastName",
"Email",
}
emptyFields := []string{}
for _, check := range checks {
// i'm having problem over here `u[check]` it's showing (invalid
operation: u[check] (type root.User does not support
indexing))
if u[check] == nil {
emptyFields = append(emptyFields, check)
}
}
err := decoder.Decode(&u)
return u, emptyFields, err
}
Just in case I added root.User here's structure for it
type User struct {
ID string
Username string
Password string
FirstName string
LastName string
Email string
PhoneNumber string
PhoneNumberExtension string
DOB time.Time
AboutMe string
}
The problem occurs as it doesn't allow me to access struct by a variable and I can't use this method which is u.check. So basically how should I make u[check] work?

Answer 1

I would suggest you manually check for zero values since it seems that you already know the fields that needs to be non-zero at compile time. However, if that is not the case, here is a simple function (using reflection) that will check for zero values in a struct.
func zeroFields(v interface{}, fields ...string) []string {
val := reflect.Indirect(reflect.ValueOf(v))
if val.Kind() != reflect.Struct {
return nil
}
var zeroes []string
for _, name := range fields {
field := val.FieldByName(name)
if !field.IsValid() {
continue
}
zero := reflect.Zero(field.Type())
// check for zero value
if reflect.DeepEqual(zero.Interface(), field.Interface()) {
zeroes = append(zeroes, name)
}
}
return zeroes
}
func main() {
x := User{
Email: "not#nil",
}
fmt.Println(zeroFields(&x, "ID", "Username", "Email", "Something", "DOB"))
}
Which would output:
[ID Username DOB]
Playground

Answer 2

This is what worked for me
for _, check := range checks {
temp := reflect.Indirect(reflect.ValueOf(&u))
fieldValue := temp.FieldByName(string(check))
if (fieldValue.Type().String() == "string" && fieldValue.Len() == 0) || (fieldValue.Type().String() != "string" && fieldValue.IsNil()) {
fmt.Println("EMPTY->", check)
emptyFields = append(emptyFields, check)
}
}