Swift 4 Decodable: Decoding complex JSON

Question

I have to decode an array of the dictionary, where the key is an enum & value is a model object.

Here is my sample JSON,

[
  {
    "nanomp4": {
      "url": "https://media.tenor.com/videos/a1da4dcf693c2187615721d866decf00/mp4", 
      "dims": [
        150, 
        138
      ], 
      "duration": 2.0, 
      "preview": "https://media.tenor.com/images/17d523e6b7c3c9a4ca64566a1890d94d/tenor.png", 
      "size": 70381
    }, 
    "nanowebm": {
      "url": "https://media.tenor.com/videos/aa983425114e32ab446f669d91611938/webm", 
      "dims": [
        150, 
        138
      ], 
      "preview": "https://media.tenor.com/images/17d523e6b7c3c9a4ca64566a1890d94d/tenor.png", 
      "size": 53888
    }, 
  },
  {
    "nanomp4": {
    "url": "https://media.tenor.com/videos/a1da4dcf693c2187615721d866decf00/mp4",
    "dims": [
          150,
          138
          ],
    "duration": 2.0,
    "preview": "https://media.tenor.com/images/17d523e6b7c3c9a4ca64566a1890d94d/tenor.png",
    "size": 70381
    },
  }
]

Here is my decoding code,

do {
    let data = try Data(contentsOf: fileURL)
    let decoder = JSONDecoder()
    let collection = try decoder.decode([[GIFFormat:Media]].self, from: data)

    print(collection)
} catch {
    print("Error in parsing/decoding JSON: \(error)")
}

Here GIFFormat is Enum & Media is the model object, and they are decoding perfectly fine.

enum GIFFormat: String, Decodable {

    case nanoMP4    = "nanomp4"
    case nanoWebM   = "nanowebm"
}

struct Media: Decodable {
    let url: URL?        
    let dims: [Int]?
    let duration: Double?
    let preview: URL?
    let size: Int64?
}

My console prints,

typeMismatch(Swift.Array<Any>, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "Expected to decode Array<Any> but found a dictionary instead.", underlyingError: nil))

Can anyone explain to me what is exactly wrong here?

Answer 1

Even though the rawValue for GIFFormat is String , GIFFormat itself is an enum. You should update

let collection = try decoder.decode([[GIFFormat:Media]].self, from: data)

to

let collection = try decoder.decode([[GIFFormat.RawValue:Media]].self, from: data)

UPDATE: In response to your comment

Now to access value, I need to use like this, collection?.first?[GIFFormat.mp4.rawValue]?.url . Which is again ugly !!

I would suggest a bit of refactoring. You can start by removing your enum altogether. Keep your Media struct. Create a new Collection struct

struct Collection: Decodable {
    let nanomp4: Media!
    let nanowebm: Media!
}

Then, you can update the above line to

let collection = try decoder.decode([Collection].self, from: data)

and your ugly line transforms into

collection.first?.nanomp4.url

NOTE: This solution assumes that you only have nanomp4 & nanowebm as your enum values. If this is not the case, then this might not be the best solution and you might have to go with the first solution.