See also

Working with JSON data and extracting relevant information from it can be frustrating. Consider the JSON response for our fetchRepos function:

[
    {
        "id": 68144965,
        "name": "JSONNode",
        "full_name": "keefmoon/JSONNode",
        "owner": {
            "login": "keefmoon",
            "id": 271298,
            "avatar_url": "https://avatars.githubusercontent.com/u/271298?v=3",
            "gravatar_id": "",
            "url": "https://api.github.com/users/keefmoon",
            "html_url": "https://github.com/keefmoon",
            "followers_url": "https://api.github.com/users/keefmoon/followers",
            //... Some more URLs
            "received_events_url": 
            "https://api.github.com/users/keefmoon/received_events",
            "type": "User",
            "site_admin": false
        },
        "private": false,
        //... more values
    }
    //... more repositories
]

If we want to get the username for the owner of the first repository, we need to do the following:

let jsonData = //... returned from the network

guard 
    let deserialised = try? JSONSerialization.jsonObject(with: jsonData, options: []), 
    let repoArray = deserialised as? [[String: Any]], 
    let firstRepo = repoArray.first, 
    let ownerDictionary = firstRepo["owner"] as? [String: Any], 
    let username = ownerDictionary["login"] as? String 
    else {
        return
}
print(username)

That's a lot of optional unwrapping and casting, just to get one value! Swift's strongly typed nature doesn't work well with JSON's loosely defined schema, which is why you have to do a lot of work to turn loosely-typed information into strongly-typed values.

To help with these problems, a number of open source frameworks are available, which make working with JSON in Swift easier. SwiftyJSON is a popular framework that can be found on GitHub at https://github.com/SwiftyJSON/SwiftyJSON.

I have also built a lightweight JSON helper called JSONNode, which can also be found on GitHub at https://github.com/keefmoon/JSONnode.

With JSONNode, you can perform the same task of retrieving the owner's username for the first repository, with the following code:

let jsonData = //... returned from the network
guard 
    let jsonNode = try? JSONNode(data: jsonData),
    let username = jsonNode[0]["owner"]["username"].string 
    else {
        return
}

print(username)

Information within JSON, of any depth, can be retrieved in one line using subscripts.

If you find JSONNode useful, let me know.