Storing Sql result sets in a nested struct and omit if empty

I am trying to store SQL query dataset in a struct and display in JSON. I have almost done it. Now the problem is if the result set of nested structs is empty then I would not like to display it.

Same problem specified here but using a pointer ends in a panic when scanning may be because I am using &user.Profile.Firstname

>2015/11/01 16:42:16 Panic recovery -> runtime error: invalid memory address or nil pointer dereference

If I remove the pointer then everything works fine just the empty field remains. I am confused how to achieve this.

package main
import (
"database/sql"
"github.com/gin-gonic/gin"
_ "github.com/go-sql-driver/mysql"
"log"
)
type User struct {
Id       int64
Username string
Email    string
Profile  Profile `json:",omitempty"`
}
type Profile struct {
Id        int64  `json:",omitempty"`
UserId    int64  `json:",omitempty"`
Firstname *string `json:",omitempty"`
Lastname  *string `json:",omitempty"`
}
var DB *sql.DB
func checkErr(err error, msg string) {
if err != nil {
log.Fatal(msg, err)
}
}
func main() {
DB, _ = sql.Open("mysql", "username:secrect@/database")
defer DB.Close()
r := gin.Default()
v1 := r.Group("api/v1/")
{
v1.GET("users", GetUsers)
}
r.Run(":8080")
}
func GetUsers(c *gin.Context) {
stmt, err := DB.Query("Select users.id, username , email , firstname , lastname from users left join profiles on users.id = profiles.user_id ")
if err != nil {
panic(err.Error())
}
defer stmt.Close()
users := []User{}
for stmt.Next() {
var user User
err := stmt.Scan(&user.Id, &user.Username, &user.Email, &user.Profile.Firstname, &user.Profile.Lastname)
if err != nil {
panic(err.Error())
}
users = append(users, user)
}
c.JSON(200, &users)
}

Output:

{
"Id": 1,
"Username": "test1",
"Email": "test1@example.com",
"Profile": {
"Firstname": "John",
"Lastname": "Doe"
}
},
{
"Id": 2,
"Username": "test2",
"Email": "test2@example.com",
"Profile": {
}
},

Assuming gin uses encoding/json under the covers, if you want to omit an empty Profile, I believe you need it to be a pointer in User:

type User struct {
....
Profile *Profile `json:",omitempty"`
}

Note the documentation:

> The "omitempty" option specifies that the field should be omitted from the encoding if the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array, slice, map, or string.

It doesn't say that the zero value of a struct will be detected.

That will leave you with some issues scanning your data from the db. You could declare a Profile, scan into it, compare to the zero profile and assign it to the User if it has data:

var user User
var profile Profile
_ = stmt.Scan(&user.Id, &user.Username, &user.Email, &profile.Firstname, &profile.Lastname)
if profile != Profile{} {
user.Profile = &profile
}

I suspect that's not the most elegant solution, but I hope it's the right direction.