Retrieve First Record of Nested Json Array

Question

I'm trying to parse the first record in an embedded JSON array and create an object based on a subset of those properties. I have this working, but based on this question, I have to think there is a more elegant/less brittle way of doing this. For a bit more background, this is a result set from a call to the musicbrainz JSON web service, and I am treating the first artists record as the artist I am looking for.

The format of the JSON is like this:

{
    "created": "2014-10-08T23:55:54.343Z",
    "count": 458,
    "offset": 0,
    "artists": [{
        "id": "83b9cbe7-9857-49e2-ab8e-b57b01038103",
        "type": "Group",
        "score": "100",
        "name": "Pearl Jam",
        "sort-name": "Pearl Jam",
        "country": "US",
        "area": {
            "id": "489ce91b-6658-3307-9877-795b68554c98",
            "name": "United States",
            "sort-name": "United States"
        },
        "begin-area": {
            "id": "10adc6b5-63bf-4b4e-993e-ed83b05c22fc",
            "name": "Seattle",
            "sort-name": "Seattle"
        },
        "life-span": {
            "begin": "1990",
            "ended": null
        },
        "aliases": [],
        "tags": []
    },
    ...
}

Here's the code I have so far. I'd like to be able to use my ArtistCollection type to get around some of the interface{} stuff, but I'm stuck as to how. I also don't want to bother with mapping all of the properties of the artist record, I'm only interested in the "name" and "id" values.

package main

import (
    "fmt"
    "encoding/json"
    )

type Artist struct {
    Id string
    Name string
}

type ArtistCollection struct {
    Artists []Artist
}

func main() {
    raw := //json formatted byte array
    var topLevel interface{}
    err := json.Unmarshal(raw, &topLevel)
    if err != nil {
        fmt.Println("Uh oh")
    } else {
        m := topLevel.(map[string]interface{})
        //this seems really hacky/brittle, there has to be a better way?
        result := (m["artists"].([]interface{})[0]).(map[string]interface{})
        artist := new(Artist)
        artist.Id = result["id"].(string)
        artist.Name = result["name"].(string)
        fmt.Println(artist)
    }
}

Requisite go playground link

score 2 · Accepted Answer · 2015-03-21 04:11:11Z

2

Define a type that matches the structure of the JSON and unmarshal to a value of that type. I use an anonymous type below. Use an array of length one to grab the first artist record:

package main

import (
    "encoding/json"
    "fmt"
)

type Artist struct {
    Id   string
    Name string
}

func main() {
    raw := // JSON formatted byte array
    var result struct {
        Artists artist
    }
    err := json.Unmarshal(raw, &result)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Printf("%#v\n", result.Artists[0])
}

playground

edited Mar 21, 2015 at 4:11

answered Oct 10, 2014 at 2:50

user4122236

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2 Comments

Sven Grosen Over a year ago

That makes sense, thank you! I, for some reason, was not expecting it to be possible to marshal to a type that only partially represented the JSON.

Dave C Over a year ago

Note the last edit (at the time of this comment) is incorrect; it does not match the code on the playground link, and will not compile. It should be Artists []Artist as in the other answer.

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