How to write Codable if array of dictionary missing one key

Question

With in Server response sometimes missing "tags" key. How we have to write codable struct for this response.

[
  {
    "product_id": 10
    "product_name": "Bulb"
    "tags": ["x", "y", "z"]
  },
  {
    "product_id": 11
    "product_name": "Wire"
  }
]

decoding like this

do {

    // decoding...
    let product_model = try JSONDecoder().decode([ProductItem].self, from: data)

} catch let error {

    print("Product list error(decoder): \(error.localizedDescription)") 
}

// Product structure

struct ProductItem: Codable {

    // variables
    let product_id: String?
    let product_name: String?
    let tags: [String]?

    // alternative keys...
    private enum CodingKeys: String, CodingKey {

        case product_id
        case product_name
        case tags // what i have to do here
    }
}

Paste json here and select SWIFT CODABLE in code template. It will generate codable struct for you. — 200_OK
– 200_OK, Commented May 6, 2019 at 8:08

Maciej Gad · Accepted Answer · 2019-05-06 08:13:52Z

3

It looks like you JSON is not correct. It should look similar to this one:

[
  {
    "product_id": 10,
    "product_name": "Bulb",
    "tags": ["x", "y", "z"]
  },
  {
    "product_id": 11,
    "product_name": "Wire"
  }
]

and for that, your structure should be similar to:

struct ProductItem: Codable {

    // variables
    let product_id: Int
    let product_name: String
    let tags: [String]?
}

You don't have to provide CodingKeys if your variables in the structure are named the same as keys in JSON object. Also, keep in mind that "product_id": 10, is a number so you should use Int not a String.

answered May 6, 2019 at 8:13

Maciej Gad

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1 Comment

Konda Yadav Over a year ago

Yes correct "CodingKeys" no need. But based on the products json coming like this.

Sweeper · Accepted Answer · 2019-05-06 09:30:50Z

2

Your JSON is missing some commas, the correct JSON is:

[
    {
        "product_id": 10,
        "product_name": "Bulb",
        "tags": ["x", "y", "z"]
    },
    {
        "product_id": 11,
        "product_name": "Wire"
    }
]

The product_id in your code is a String, whereas in your JSON, it is a number.

Swift can actually handle missing keys like this, as long as you make the property optional, which you have correctly done here. tags will be assigned nil when there is no key in the JSON. So you don't really have to do anything other than changing product_id to be a Int.

Your property names can also be renamed to be more Swifty if you use convertFromSnakeCase option when decoding:

struct ProductItem: Codable {

    let productId: Int?
    let productName: String?
    let tags: [String]?
}

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let decoded = try! decoder.decode([ProductItem].self, from: data)
print(decoded[1].tags) // nil

edited May 6, 2019 at 9:30

answered May 6, 2019 at 8:16

Sweeper

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11 Comments

vadian Over a year ago

You can write the code even more Swifty by removing the CodingKeys and adding the .convertFromSnakeCase strategy 😉

Konda Yadav Over a year ago

if all keys coming correctly, this is correct. if tags key missing in few products. what we have to do.

Sweeper Over a year ago

@KondaYadav It doesn't matter. You don't have to do anything. ProductItem.tags will simply be nil. It won't crash. Do you want to assign it a default value?

Konda Yadav Over a year ago

@Sweeper I'm getting like this ERROR: The data couldn’t be read because it isn’t in the correct format.

Sweeper Over a year ago

@KondaYadav Ah that's because your JSON is still invalid. I thought you fixed it in your edit, but the JSON still seems to be missing some commas. You need to somehow fix your server then.

|

Konda Yadav · Accepted Answer · 2019-05-06 10:29:16Z

@dahiya_boy thank you. This below code working fine.

struct ProductItem : Codable {

        let productId : Int?
        let productName : String?
        let tags : [String]?

        enum CodingKeys: String, CodingKey {
                case productId = "product_id"
                case productName = "product_name"
                case tags = "tags"
        }

        init(from decoder: Decoder) throws {
                let values = try decoder.container(keyedBy: CodingKeys.self)
                productId = try values.decodeIfPresent(Int.self, forKey: .productId)
                productName = try values.decodeIfPresent(String.self, forKey: .productName)
                tags = try values.decodeIfPresent([String].self, forKey: .tags)
        }

}

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