Decode Custom Json with Decodable - json

Question

I have this Json:
{ "first": {
"house": [
"small"
]
}, "second": {
"house": [
"small"
] }, "third": {
"car": [
"fast",
"economic"
] }, "fourth": {
"car": [
"fast",
"economic"
] }, "fifth": {
"car": [
"fast",
"economic"
],
"ice": [
"round",
"tasty"
],
"tree": [
"big",
"small"
] } }
I tried to set up a structure with Decodable but I do not get it to work:
struct secondLayer: Codable {
let exchange: [String: [String]]
}
struct decodeJson: Codable {
let symbol: [String: [secondLayer]]
static func decode(jsonString: String) - [decodeJson] {
var output = [decodeJson]()
let decode = JSONDecoder()
do {
let json = jsonString.data(using: .utf8)
output = try! decode.decode([decodeJson].self, from: json!)
} catch {
print(error.localizedDescription)
}
return output
}
}
I get this Error:
Fatal error: 'try!' expression unexpectedly raised an error:
Swift.DecodingError.typeMismatch(Swift.Array<Any>,
Swift.DecodingError.Context(codingPath: [], debugDescription:
"Expected to decode Array<Any but found a dictionary instead.",
underlyingError: nil)): file
/BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-900.0.74.1/src/swift/stdlib/public/core/ErrorType.swift,
line 181
I tried some modification but I do not get it to work.

Answer 1

The error message
"Expected to decode Array<Any> but found a dictionary instead."
is very clear. You want to decode an array ([decodeJson]) but the root object is a dictionary (starting with {)
Your code cannot work anyway. There are no keys exchange and symbol in the JSON.
Basically there are two ways to decode that JSON:
If all keys are dynamic you cannot decode the JSON to structs. You have to decode it to [String:[String:[String]]]. In this case Codable has no benefit over traditional JSONSerialization.
struct DecodeJson: Codable {
static func decode(jsonString: String) -> [String:[String:[String]]] {
var output = [String:[String:[String]]]()
let decoder = JSONDecoder()
do {
let json = Data(jsonString.utf8)
output = try decoder.decode([String:[String:[String]]].self, from: json)
print(output)
} catch {
print(error.localizedDescription)
}
return output
}
}
Or if the ordinal keys first, second etc are static use an umbrella struct
struct Root : Codable {
let first : [String:[String]]
let second : [String:[String]]
let third : [String:[String]]
let fourth : [String:[String]]
let fifth : [String:[String]]
}
struct DecodeJson {
static func decode(jsonString: String) -> Root? {
let decoder = JSONDecoder()
do {
let json = Data(jsonString.utf8)
let output = try decoder.decode(Root.self, from: json)
return output
} catch {
print(error.localizedDescription)
return nil
}
}
}
Of course you can decode house, car etc into a struct but this requires a custom initializer for each struct because you have to decode a single array manually with unkeyedContainer