Convert query result from struct to string for another Golang package - sql

Question

I have searched for a solution on the net and in SO, but found nothing that apply to return values. It is a simple sql query with several rows that I want to return. Error handling not included:
func Fetch(query string) (string) {
type User struct{
id string
name string
}
rows, err := db.Query(query)
users := make([]*User, 0)
for rows.Next() {
user := new(User)
err := rows.Scan(&user.id, &user.name)
users = append(users, user)
}
return(users)
}
I get this error when compiling:
cannot use users (type []*User) as type string in return argument
How should I do to get a correct return value?
The expected input is
JD John Doe --OR-- {id:"JD",name:"John Doe"}

Answer 1

Add this to your code:
type userSlice []*User
func (us userSlice) String() string{
var s []string
for _, u := range us {
if u != nil {
s = append(s, fmt.Sprintf("%s %s", u.id, u.name))
}
}
return strings.Join(s, "\n")
}
type User struct{
id string
name string
}
In your Fetch function replace the last return statement like this:
func Fetch(query string) (string) {
// Note that we declare the User type outside the function.
rows, err := db.Query(query)
users := make([]*User, 0)
for rows.Next() {
user := new(User)
err := rows.Scan(&user.id, &user.name)
users = append(users, user)
}
return(userSlice(users).String()) // Replace this line in your code
}

Answer 2

If you have to return a String you can use the encoding/json package to serialize your user object, but you have to use fields that begin with capital letters for them to be exported. See the full example:
import (
"encoding/json"
)
func Fetch(query string) (string) {
type User struct{
Id string // <-- CHANGED THIS LINE
Name string // <-- CHANGED THIS LINE
}
rows, err := db.Query(query)
users := make([]*User, 0)
for rows.Next() {
user := new(User)
err := rows.Scan(&user.id, &user.name)
users = append(users, user)
}
return(ToJSON(users)) // <-- CHANGED THIS LINE
}
func ToJSON(obj interface{}) (string) {
res, err := json.Marshal(obj)
if err != nil {
panic("error with json serialization " + err.Error())
}
return string(res)
}