Swift 4 Decodable: Decoding complex JSON - ios

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.