How to unmarshal two json with same internal structure into one single golang struct?

I have two json files with following structure

{
 "cast": [
        {
            "url": "carey-mulligan",
            "name": "Carey Mulligan",
            "role": "Actress"
        },
        {
            "url": "leonardo-dicaprio",
            "name": "Leonardo DiCaprio",
            "role": "Actor"
        },
        .
        .
        .
         ]
}

and

{
 "movie": [
        {
            "url": "carey-mulligan",
            "name": "Carey Mulligan",
            "role": "Actress"
        },
        {
            "url": "leonardo-dicaprio",
            "name": "Leonardo DiCaprio",
            "role": "Actor"
        },
        .
        .
        .
         ]
}

as you can see internal structure of the json is same for cast and movie. I want to unmarshel these json file into the same golang structure. But i am not able to give two name tags (cast and movie) for same struct element. I want something like

type Detail struct {
	Name string `json:"name"`
	Url  string `json:"url"`
	Role string `json:"role"`
}

type Info struct {
	Detail []Detail `json:"cast or movie"`
}

In which case Detail could parse both cast and movie.

Here is my current code

// RIMAGE project main.go
package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
)

const (
	website = "https://data.moviebuff.com/"
)

func main() {
	fmt.Println("Hello World!")
	content, err := ioutil.ReadFile("data/great-getsby")
	if err != nil {
		panic(err)
	}

	var info Info

	err = json.Unmarshal(content, &info)
	if err != nil {
		panic(err)
	}

	fmt.Println(info.Detail)
}

type Detail struct {
	Name string `json:"name"`
	Url  string `json:"url"`
	Role string `json:"role"`
}

type Info struct {
	Detail []Detail `json:"cast" json:"movie"
}

but it only works for first tag "cast" and gives nill in case json contain the movie.

Thanks in advance.

You can use type Info map[string][]Detail instead of your struct.
Try it on the <kbd>Go playground</kbd>

Or you can use both types in your structure, and make method Details() which will return right one:

type Info struct {
	CastDetails  []Detail `json:"cast"`
	MovieDetails []Detail `json:"movie"`
}

func (i Info) Details() []Detail {
	if i.CastDetails == nil {
		return i.MovieDetails
	}
	return i.CastDetails
}

Try it on the <kbd>Go playground</kbd>

Try anonymous field in struct:

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
)

type Detail struct {
	Name string `json:"name"`
	Url  string `json:"url"`
	Role string `json:"role"`
}

type Cast struct {
	Detail []Detail `json:"cast"`
}

type Movie struct {
	Detail []Detail `json:"movie"`
}

type Info struct {
	Cast
	Movie
}

func (i *Info) getDetails() []Detail {
	if len(i.Cast.Detail) > 0 {
		return i.Cast.Detail
	}
	return i.Movie.Detail
}

func main() {
	cast, _ := ioutil.ReadFile("./cast.json")
	movie, _ := ioutil.ReadFile("./movie.json")
    
	var cInfo Info
	err := json.Unmarshal(cast, &cInfo)
	fmt.Printf("cast: %+v\n", &cInfo)
	fmt.Printf("err: %v\n", err)
	fmt.Printf("details: %v\n", cInfo.getDetails())

	var mInfo Info
	err = json.Unmarshal(movie, &mInfo)
	fmt.Printf("movie: %+v\n", &mInfo)
	fmt.Printf("err: %v\n", err)
	fmt.Printf("details: %v\n", mInfo.getDetails())
}

Things to note:

• One more level of indirection: to access 'Details' field, you need to access either 'Cast' or 'Movie' field first in Info first.
• Better provide an access function for 'Details' ('getDetail' in this example)

If you dig far enough down into encoding/json you'll get to https://github.com/golang/go/blob/master/src/encoding/json/encode.go and the following:

		tag := sf.Tag.Get("json")
		if tag == "-" {
			continue
		}

So it gets one json tag and keeps on going.

You could always go with RoninDev's solution and just copy it over when done.