Parsing a nested JSON using Decodable

Question

My JSON structure looks like this:

{
    "code": 200,
    "status": "Ok",
    "etag": "7232324423",
    "data": {
        "offset": 0,
        "limit": 25,
        "results": [{
                "id": 1011244,
                "name": "Miss Nesbit",
                "description": "",
                "modified": "2018-04-04T20:15:35-0400",
                "thumbnail": {
                    "path": "http://i.annihil.us/u/prod/i/mg/8/70/4c002efc322e3",
                    "extension": "jpg"
                }
            },
            {
                "id": 1011244,
                "name": "Miss Solis",
                "description": "",
                "modified": "2018-09-04T20:15:35-0400",
                "thumbnail": {
                    "path": "http://i.annihil.us/u/prod/i/mg/8/70/4c002efc382e3",
                    "extension": "jpg"
                }
            }
        ]
    }
}

I want to parse the results in a struct as follows:

struct Character: Codable {
    let id: Int
    let name: String
    let thumbnail: Thumbnail
    let description: String
}

However I'm a bit confused about where I specify I only want the results part ? Would I do it when implementing Decodable as follows?

let container = try decoder.container(keyedBy: CodingKeys.self)
let data = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .data)
let results = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .results)

Or do we have to map out each nested section? ANy help or guidance would be so appreciated! :)

Character is a native Swift type. You should choose an alternative name for your struct — Leo Dabus
– Leo Dabus, Commented Sep 28, 2018 at 23:38

Fabian · Accepted Answer · 2018-09-28 23:19:19Z

3

Mapping out the relevant keys is necessary to drill down for you, yes.

You can use app.quicktype.io to get started fast and remove the non-relevant keys if you really don‘t want to parse the rest or leave it there if you may want to use it later.

answered Sep 28, 2018 at 23:19

Fabian

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3 Comments

vanilla_splsh Over a year ago

Thanks for the response. So in this case, would : code, status, etag, data be relevant and then i can drill down within data to get the results? I thought I'd be able to ignore the outer part but I guess i'm wrong!

Fabian Over a year ago

@vanilla_splsh Only let data: DataStruct is relevant from the first level, so you and Swift know there is a data-field you can drill into. This DataStruct then has a let results: [CharacterStruct] field, so you can access the array encoded in JSON as an Array inside Swift. Here is a tutorial on the Codable-API. You can ignore everything except where he embeds one struct into another and an array into a struct/class. If you want to do this manually you can use differing CodingKey enums per level & class.

vanilla_splsh Over a year ago

Thank you for your help, makes complete sense now and I got it working!

aunnnn · Accepted Answer · 2018-09-28 23:58:01Z

2

You can use my extension helper NestedDecodable, which allows you to extract Decodable from a keyPath. It adds this method to JSONDecoder:

decoder.decode(Class, from: Data, keyPath: String)

A key path specifies the nested path to the model you want, separated by .

So using your example, this works (tested):

let characters = try decoder.decode([Character].self, from: data, keyPath: "data.results")

Internally, it creates a wrapper struct to hold your target Decodable class, split keyPath by ., then for-loop each key down until it reaches the final keyed decoding container, decode that model and returns. Ref

edited Sep 28, 2018 at 23:58

answered Sep 28, 2018 at 23:40

aunnnn

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