Declaring a struct for json objects - json

Question

I have a JSON response object from a API like that:
[
{
"peoples": {
"1": {"name": "Jhon", "age": 123},
"2": {"name": "Jhon", "age": 123},
"3": {"name": "Jhon", "age": 123},
"4": {"name": "Jhon", "age": 123},
"_object": true,
"_timestamp": "2020-08-05T07:05:55.509Z",
"_writable": false
}
}
]
The parameters: peoples, _object, _timestamp and _writable is fixed. The dynamic values are the 1,2,3,4...n parameters.
The qty of peoples in that struct can be more then 4 or can be 1. Have any elegant solution for create a Struct object or a json.Unmarshal for that?

Answer 1

Borrowing the input example from Sarath Sadasivan Pillai (see comment), here (link to Playground example) is a way to do it with map[string]json.RawMessage and a custom unmarshal function:
package main
import (
"encoding/json"
"fmt"
"strconv"
"time"
)
type Person struct {
Name string `json:"name"`
Age int `json:"age"`
}
type Keywords struct {
Object bool `json:"_object"`
Timestamp time.Time `json:"_timestamp"`
Writable bool `json:"_writable"`
}
type Decoded struct {
People map[string]Person // or perhaps just []Person
Info Keywords
}
var input []byte = []byte(`{
"1": {"name": "Jhon", "age": 123},
"2": {"name": "Jhon", "age": 123},
"3": {"name": "Jhon", "age": 123},
"4": {"name": "Jhon", "age": 123},
"_object": true,
"_timestamp": "2020-08-05T07:05:55.509Z",
"_writable": false
}`)
// Unmarshal json in the input format outlined by
// the example above: a map of numeric strings to Name/Age pair,
// plus some keywords.
func (d *Decoded) UnmarshalJSON(data []byte) error {
if err := json.Unmarshal(data, &d.Info); err != nil {
return err
}
var m map[string]json.RawMessage
if err := json.Unmarshal(data, &m); err != nil {
return err
}
if d.People == nil {
d.People = make(map[string]Person)
}
for k := range m {
// This is the hard part: you must choose how
// to decide whether to decode this as a Person.
// Here, we use strconv.Atoi() as in the example
// by Sarath Sadasivan Pillai, but there are as
// many options as you can think of.
//
// For instance, another method would be to try
// decoding the json.RawMessage as a Person. It's
// also not clear whether the numeric values imply
// some particular ordering, which maps discard.
// (If these come out in order, that's just luck.)
if _, err := strconv.Atoi(k); err != nil {
continue
}
var p Person
if err := json.Unmarshal(m[k], &p); err != nil {
return err
}
d.People[k] = p
}
return nil
}
func main() {
var x Decoded
err := json.Unmarshal(input, &x)
if err != nil {
fmt.Printf("failed: %v\n", err)
} else {
fmt.Printf("succeeded:\n%#v\n", x.Info)
for k := range x.People {
fmt.Printf("person %q = %#v\n", k, x.People[k])
}
}
}