Decoding this kind of JSON with Codable

Question

I have a json that looks like this:

let jsonString = """
{
    "data": [
        {
            "name": "Apple",
            "price": 44,
            "available": true
        },
        {
            "name": "Pear",
            "price": 27,
            "available": false
        }
    ],
    "some_stuff": [],
    "some_other_stuff": []
}"""

My goal is to parse the content of the data array, specifically in a struct that doesn't care about the availibility attribute. I don't care about the some_stuff and some_other_stuff returned is that json.

First question: Can I ignore these properties event if they are part of the response at the same level as "data" which I'm interested in? If so, how do I represent and empty array of a type I ignore because I only get empty arrays? (For that part, I chose to represent it as an array of arbitrary chosen type Int?)

I created a struct:

struct Fruit: Codable {
    let name: String
    let price: Int
}

And a kind of super struct above:

struct WholeResponse: Codable {
    let data: [Fruit]
    let someStuff: [Int?]
    let someOtherStuff: [Int?]

    enum CodingKeys: String, CodingKey {
        case data
        case someStuff = "some_stuff"
        case someOtherStuff = "some_other_stuff"
    }

    struct Fruit: Codable {
        let name: String
        let price: Int
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let data = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .data)
        name = try data.decode(String.self, forKey: .name)
        price = try data.decode(Int.self, forKey: .price)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        var data = container.nestedContainer(keyedBy: CodingKeys.self, forKey: .data)
        try data.encode(name, forKey: .name)
        try data.encode(price, forKey: .price)
    }
}

But I found myself pretty stuck after doing this:

let jsonData = jsonString.data(using: .utf8)!
let jsonDecoder = JSONDecoder()

let fruits = try jsonDecoder.decode(WholeResponse.self, from: jsonData)

I think I am missing something about the representation of my data and perhaps complicating the thing but can you help me get this data array parsed?

If you don't care about someStuff and someOtherStuff then just delete the let lines where you declare properties for them in your struct. Also you can delete your initFrom and decode because the right thing will happen all by itself. — matt
– matt, Commented Oct 14, 2019 at 21:34

matt · Accepted Answer · 2019-10-14 21:35:28Z

2

First just delete everything you don't want:

struct WholeResponse: Codable {
    let data: [Fruit]

    struct Fruit: Codable {
        let name: String
        let price: Int
    }
}

Then, similar to what you had before, say

let response = try jsonDecoder.decode(WholeResponse.self, from: jsonData)
let fruits = response.data

answered Oct 14, 2019 at 21:35

matt

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