Validate struct field if it exists

Question

I\'m POSTing a JSON user object to my Golang application where I decode the \'req.body\' into a \'User\' struct.

err := json.NewDecoder(req.Body).Decode(user)
//         


        

Answer 1

You can use a pointer to a string:

type User struct {
    Name     string  `json:"name,omitempty"`
    Username *string `json:"username,omitempty"`
    Email    string  `json:"email,omitempty"`
    Town     string  `json:"town,omitempty"`
    //more fields here
}

func main() {
    var u, u2 User
    json.Unmarshal([]byte(`{"username":"hi"}`), &u)
    fmt.Println("username set:", u.Username != nil, *u.Username)
    json.Unmarshal([]byte(`{}`), &u2)
    fmt.Println("username set:", u2.Username != nil)
    fmt.Println("Hello, playground")
}

playground