Unmarshal unknown JSON fields without structs - go

Question

I am trying to unmarshal a JSON object which has an optional array, I am doing this without an array and this is what I got so far:
import (
"encoding/json"
"fmt"
)
func main() {
jo := `
{
"given_name": "Akshay Raj",
"name": "Akshay",
"country": "New Zealand",
"family_name": "Gollahalli",
"emails": [
"name#example.com"
]
}
`
var raw map[string]interface{}
err := json.Unmarshal([]byte(jo), &raw)
if err != nil {
panic(err)
}
fmt.Println(raw["emails"][0])
}
The emails field might or might not come sometime. I know I can use struct and unmarshal it twice for with and without array. When I try to get the index 0 of raw["emails"][0] I get the following error
invalid operation: raw["emails"][0] (type interface {} does not support indexing)
Is there a way to get the index of the emails field?
Update 1
I can do something like this fmt.Println(raw["emails"].([]interface{})[0]) and it works. Is this the only way?

Answer 1

The easiest way is with a struct. There's no need to unmarshal twice.
type MyStruct struct {
// ... other fields
Emails []string `json:"emails"`
}
This will work, regardless of whether the JSON input contains the emails field. When it is missing, your resulting struct will just have an uninitialized Emails field.

Answer 2

You can use type assertions. The Go tutorial on type assertions is here.
A Go playground link applying type assertions to your problem is here. For ease of reading, that code is replicated below:
package main
import (
"encoding/json"
"fmt"
)
func main() {
jo := `
{
"given_name": "Akshay Raj",
"name": "Akshay",
"country": "New Zealand",
"family_name": "Gollahalli",
"emails": [
"name#example.com"
]
}
`
var raw map[string]interface{}
err := json.Unmarshal([]byte(jo), &raw)
if err != nil {
panic(err)
}
emails, ok := raw["emails"]
if !ok {
panic("do this when no 'emails' key")
}
emailsSlice, ok := emails.([]interface{})
if !ok {
panic("do this when 'emails' value is not a slice")
}
if len(emailsSlice) == 0 {
panic("do this when 'emails' slice is empty")
}
email, ok := (emailsSlice[0]).(string)
if !ok {
panic("do this when 'emails' slice contains non-string")
}
fmt.Println(email)
}

Answer 3

As always you can use additional libraries for work with your json data. For example with gojsonq package it will like so:
package main
import (
"fmt"
"github.com/thedevsaddam/gojsonq"
)
func main() {
json := `
{
"given_name": "Akshay Raj",
"name": "Akshay",
"country": "New Zealand",
"family_name": "Gollahalli",
"emails": [
"name#example.com"
]
}
`
first := gojsonq.New().JSONString(json).Find("emails.[0]")
if first != nil {
fmt.Println(first.(string))
} else {
fmt.Println("There isn't emails")
}
}