How to decode a property with type of JSON dictionary in Swift [45] decodable protocol

With some inspiration from this gist I found, I wrote some extensions for UnkeyedDecodingContainer and KeyedDecodingContainer. You can find a link to my gist here. By using this code you can now decode any Array<Any> or Dictionary<String, Any> with the familiar syntax:

let dictionary: [String: Any] = try container.decode([String: Any].self, forKey: key)

or

let array: [Any] = try container.decode([Any].self, forKey: key)

Edit: there is one caveat I have found which is decoding an array of dictionaries [[String: Any]] The required syntax is as follows. You'll likely want to throw an error instead of force casting:

let items: [[String: Any]] = try container.decode(Array<Any>.self, forKey: .items) as! [[String: Any]]

EDIT 2: If you simply want to convert an entire file to a dictionary, you are better off sticking with api from JSONSerialization as I have not figured out a way to extend JSONDecoder itself to directly decode a dictionary.

guard let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] else {
  // appropriate error handling
  return
}

The extensions

// Inspired by https://gist.github.com/mbuchetics/c9bc6c22033014aa0c550d3b4324411a

struct JSONCodingKeys: CodingKey {
    var stringValue: String

    init?(stringValue: String) {
        self.stringValue = stringValue
    }

    var intValue: Int?

    init?(intValue: Int) {
        self.init(stringValue: "\(intValue)")
        self.intValue = intValue
    }
}


extension KeyedDecodingContainer {

    func decode(_ type: Dictionary<String, Any>.Type, forKey key: K) throws -> Dictionary<String, Any> {
        let container = try self.nestedContainer(keyedBy: JSONCodingKeys.self, forKey: key)
        return try container.decode(type)
    }

    func decodeIfPresent(_ type: Dictionary<String, Any>.Type, forKey key: K) throws -> Dictionary<String, Any>? {
        guard contains(key) else { 
            return nil
        }
        guard try decodeNil(forKey: key) == false else { 
            return nil 
        }
        return try decode(type, forKey: key)
    }

    func decode(_ type: Array<Any>.Type, forKey key: K) throws -> Array<Any> {
        var container = try self.nestedUnkeyedContainer(forKey: key)
        return try container.decode(type)
    }

    func decodeIfPresent(_ type: Array<Any>.Type, forKey key: K) throws -> Array<Any>? {
        guard contains(key) else {
            return nil
        }
        guard try decodeNil(forKey: key) == false else { 
            return nil 
        }
        return try decode(type, forKey: key)
    }

    func decode(_ type: Dictionary<String, Any>.Type) throws -> Dictionary<String, Any> {
        var dictionary = Dictionary<String, Any>()

        for key in allKeys {
            if let boolValue = try? decode(Bool.self, forKey: key) {
                dictionary[key.stringValue] = boolValue
            } else if let stringValue = try? decode(String.self, forKey: key) {
                dictionary[key.stringValue] = stringValue
            } else if let intValue = try? decode(Int.self, forKey: key) {
                dictionary[key.stringValue] = intValue
            } else if let doubleValue = try? decode(Double.self, forKey: key) {
                dictionary[key.stringValue] = doubleValue
            } else if let nestedDictionary = try? decode(Dictionary<String, Any>.self, forKey: key) {
                dictionary[key.stringValue] = nestedDictionary
            } else if let nestedArray = try? decode(Array<Any>.self, forKey: key) {
                dictionary[key.stringValue] = nestedArray
            }
        }
        return dictionary
    }
}

extension UnkeyedDecodingContainer {

    mutating func decode(_ type: Array<Any>.Type) throws -> Array<Any> {
        var array: [Any] = []
        while isAtEnd == false {
            // See if the current value in the JSON array is `null` first and prevent infite recursion with nested arrays.
            if try decodeNil() {
                continue
            } else if let value = try? decode(Bool.self) {
                array.append(value)
            } else if let value = try? decode(Double.self) {
                array.append(value)
            } else if let value = try? decode(String.self) {
                array.append(value)
            } else if let nestedDictionary = try? decode(Dictionary<String, Any>.self) {
                array.append(nestedDictionary)
            } else if let nestedArray = try? decode(Array<Any>.self) {
                array.append(nestedArray)
            }
        }
        return array
    }

    mutating func decode(_ type: Dictionary<String, Any>.Type) throws -> Dictionary<String, Any> {

        let nestedContainer = try self.nestedContainer(keyedBy: JSONCodingKeys.self)
        return try nestedContainer.decode(type)
    }
}

I have played with this problem, too, and finally wrote a simple library for working with “generic JSON” types. (Where “generic” means “with no structure known in advance”.) Main point is representing the generic JSON with a concrete type:

public enum JSON {
    case string(String)
    case number(Float)
    case object([String:JSON])
    case array([JSON])
    case bool(Bool)
    case null
}

This type can then implement Codable and Equatable.

You can create metadata struct which confirms to Decodable protocol and use JSONDecoder class to create object from data by using decode method like below

let json: [String: Any] = [
    "object": "customer",
    "id": "4yq6txdpfadhbaqnwp3",
    "email": "john.doe@example.com",
    "metadata": [
        "link_id": "linked-id",
        "buy_count": 4
    ]
]

struct Customer: Decodable {
    let object: String
    let id: String
    let email: String
    let metadata: Metadata
}

struct Metadata: Decodable {
    let link_id: String
    let buy_count: Int
}

let data = try JSONSerialization.data(withJSONObject: json, options: .prettyPrinted)

let decoder = JSONDecoder()
do {
    let customer = try decoder.decode(Customer.self, from: data)
    print(customer)
} catch {
    print(error.localizedDescription)
}

I came with a slightly different solution.

Let's suppose we have something more than a simple [String: Any] to parse were Any might be an array or a nested dictionary or a dictionary of arrays.

Something like this:

var json = """
{
  "id": 12345,
  "name": "Giuseppe",
  "last_name": "Lanza",
  "age": 31,
  "happy": true,
  "rate": 1.5,
  "classes": ["maths", "phisics"],
  "dogs": [
    {
      "name": "Gala",
      "age": 1
    }, {
      "name": "Aria",
      "age": 3
    }
  ]
}
"""

Well, this is my solution:

public struct AnyDecodable: Decodable {
  public var value: Any

  private struct CodingKeys: CodingKey {
    var stringValue: String
    var intValue: Int?
    init?(intValue: Int) {
      self.stringValue = "\(intValue)"
      self.intValue = intValue
    }
    init?(stringValue: String) { self.stringValue = stringValue }
  }

  public init(from decoder: Decoder) throws {
    if let container = try? decoder.container(keyedBy: CodingKeys.self) {
      var result = [String: Any]()
      try container.allKeys.forEach { (key) throws in
        result[key.stringValue] = try container.decode(AnyDecodable.self, forKey: key).value
      }
      value = result
    } else if var container = try? decoder.unkeyedContainer() {
      var result = [Any]()
      while !container.isAtEnd {
        result.append(try container.decode(AnyDecodable.self).value)
      }
      value = result
    } else if let container = try? decoder.singleValueContainer() {
      if let intVal = try? container.decode(Int.self) {
        value = intVal
      } else if let doubleVal = try? container.decode(Double.self) {
        value = doubleVal
      } else if let boolVal = try? container.decode(Bool.self) {
        value = boolVal
      } else if let stringVal = try? container.decode(String.self) {
        value = stringVal
      } else {
        throw DecodingError.dataCorruptedError(in: container, debugDescription: "the container contains nothing serialisable")
      }
    } else {
      throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Could not serialise"))
    }
  }
}

Try it using

let stud = try! JSONDecoder().decode(AnyDecodable.self, from: jsonData).value as! [String: Any]
print(stud)

When I found the old answer, I only tested a simple JSON object case but not an empty one which will cause a runtime exception like @slurmomatic and @zoul found. Sorry for this issue.

So I try another way by having a simple JSONValue protocol, implement the AnyJSONValue type erasure struct and use that type instead of Any. Here's an implementation.

public protocol JSONType: Decodable {
    var jsonValue: Any { get }
}

extension Int: JSONType {
    public var jsonValue: Any { return self }
}
extension String: JSONType {
    public var jsonValue: Any { return self }
}
extension Double: JSONType {
    public var jsonValue: Any { return self }
}
extension Bool: JSONType {
    public var jsonValue: Any { return self }
}

public struct AnyJSONType: JSONType {
    public let jsonValue: Any

    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()

        if let intValue = try? container.decode(Int.self) {
            jsonValue = intValue
        } else if let stringValue = try? container.decode(String.self) {
            jsonValue = stringValue
        } else if let boolValue = try? container.decode(Bool.self) {
            jsonValue = boolValue
        } else if let doubleValue = try? container.decode(Double.self) {
            jsonValue = doubleValue
        } else if let doubleValue = try? container.decode(Array<AnyJSONType>.self) {
            jsonValue = doubleValue
        } else if let doubleValue = try? container.decode(Dictionary<String, AnyJSONType>.self) {
            jsonValue = doubleValue
        } else {
            throw DecodingError.typeMismatch(JSONType.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Unsupported JSON tyep"))
        }
    }
}

And here is how to use it when decoding

metadata = try container.decode ([String: AnyJSONValue].self, forKey: .metadata)

The problem with this issue is that we must call value.jsonValue as? Int. We need to wait until Conditional Conformance land in Swift, that would solve this problem or at least help it to be better.

[Old Answer]

I post this question on the Apple Developer forum and it turns out it is very easy.

I can do

metadata = try container.decode ([String: Any].self, forKey: .metadata)

in the initializer.

It was my bad to miss that in the first place.

If you use SwiftyJSON to parse JSON, you can update to 4.1.0 which has Codable protocol support. Just declare metadata: JSON and you're all set.

import SwiftyJSON

struct Customer {
  let id: String
  let email: String
  let metadata: JSON
}

I have written an article and repo that helps in adding [String: Any] support for Codable for decoding as well as encoding.

https://medium.com/nerd-for-tech/string-any-support-for-codable-4ba062ce62f2

This improves on decodable aspect and also add encodable support as solution given by in https://stackoverflow.com/a/46049763/9160905

what you will be able to achieve:

json:

https://i.stack.imgur.com/7TVwt.png

sample code:

https://i.stack.imgur.com/HK5zX.png

You might have a look at BeyovaJSON

import BeyovaJSON

struct Customer: Codable {
  let id: String
  let email: String
  let metadata: JToken
}

//create a customer instance

customer.metadata = ["link_id": "linked-id","buy_count": 4]

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted 
print(String(bytes: try! encoder.encode(customer), encoding: .utf8)!)

Here is more generic (not only [String: Any], but [Any] can decoded) and encapsulated approach (separate entity is used for that) inspired by @loudmouth answer.

Using it will look like:

extension Customer: Decodable {
  public init(from decoder: Decoder) throws {
    let selfContainer = try decoder.container(keyedBy: CodingKeys.self)
    id = try selfContainer.decode(.id)
    email = try selfContainer.decode(.email)
    let metadataContainer: JsonContainer = try selfContainer.decode(.metadata)
    guard let metadata = metadataContainer.value as? [String: Any] else {
      let context = DecodingError.Context(codingPath: [CodingKeys.metadata], debugDescription: "Expected '[String: Any]' for 'metadata' key")
      throw DecodingError.typeMismatch([String: Any].self, context)
    }
    self.metadata = metadata
  }

  private enum CodingKeys: String, CodingKey {
    case id, email, metadata
  }
}

JsonContainer is a helper entity we use to wrap decoding JSON data to JSON object (either array or dictionary) without extending *DecodingContainer (so it won't interfere with rare cases when a JSON object is not meant by [String: Any]).

struct JsonContainer {

  let value: Any
}

extension JsonContainer: Decodable {

  public init(from decoder: Decoder) throws {
    if let keyedContainer = try? decoder.container(keyedBy: Key.self) {
      var dictionary = [String: Any]()
      for key in keyedContainer.allKeys {
        if let value = try? keyedContainer.decode(Bool.self, forKey: key) {
          // Wrapping numeric and boolean types in `NSNumber` is important, so `as? Int64` or `as? Float` casts will work
          dictionary[key.stringValue] = NSNumber(value: value)
        } else if let value = try? keyedContainer.decode(Int64.self, forKey: key) {
          dictionary[key.stringValue] = NSNumber(value: value)
        } else if let value = try? keyedContainer.decode(Double.self, forKey: key) {
          dictionary[key.stringValue] = NSNumber(value: value)
        } else if let value = try? keyedContainer.decode(String.self, forKey: key) {
          dictionary[key.stringValue] = value
        } else if (try? keyedContainer.decodeNil(forKey: key)) ?? false {
          // NOP
        } else if let value = try? keyedContainer.decode(JsonContainer.self, forKey: key) {
          dictionary[key.stringValue] = value.value
        } else {
          throw DecodingError.dataCorruptedError(forKey: key, in: keyedContainer, debugDescription: "Unexpected value for \(key.stringValue) key")
        }
      }
      value = dictionary
    } else if var unkeyedContainer = try? decoder.unkeyedContainer() {
      var array = [Any]()
      while !unkeyedContainer.isAtEnd {
        let container = try unkeyedContainer.decode(JsonContainer.self)
        array.append(container.value)
      }
      value = array
    } else if let singleValueContainer = try? decoder.singleValueContainer() {
      if let value = try? singleValueContainer.decode(Bool.self) {
        self.value = NSNumber(value: value)
      } else if let value = try? singleValueContainer.decode(Int64.self) {
        self.value = NSNumber(value: value)
      } else if let value = try? singleValueContainer.decode(Double.self) {
        self.value = NSNumber(value: value)
      } else if let value = try? singleValueContainer.decode(String.self) {
        self.value = value
      } else if singleValueContainer.decodeNil() {
        value = NSNull()
      } else {
        throw DecodingError.dataCorruptedError(in: singleValueContainer, debugDescription: "Unexpected value")
      }
    } else {
      let context = DecodingError.Context(codingPath: [], debugDescription: "Invalid data format for JSON")
      throw DecodingError.dataCorrupted(context)
    }
  }

  private struct Key: CodingKey {
    var stringValue: String

    init?(stringValue: String) {
      self.stringValue = stringValue
    }

    var intValue: Int?

    init?(intValue: Int) {
      self.init(stringValue: "\(intValue)")
      self.intValue = intValue
    }
  }
}

Note that numberic and boolean types are backed by NSNumber, else something like this won't work:

if customer.metadata["keyForInt"] as? Int64 { // as it always will be nil

I have made a pod to facilitate the way the decoding + encoding [String: Any], [Any]. And this provides encode or decode the optional properties, here https://github.com/levantAJ/AnyCodable

pod 'DynamicCodable', '1.0'

How to use it:

import DynamicCodable

struct YourObject: Codable {
    var dict: [String: Any]
    var array: [Any]
    var optionalDict: [String: Any]?
    var optionalArray: [Any]?

    enum CodingKeys: String, CodingKey {
        case dict
        case array
        case optionalDict
        case optionalArray
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        dict = try values.decode([String: Any].self, forKey: .dict)
        array = try values.decode([Any].self, forKey: .array)
        optionalDict = try values.decodeIfPresent([String: Any].self, forKey: .optionalDict)
        optionalArray = try values.decodeIfPresent([Any].self, forKey: .optionalArray)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(dict, forKey: .dict)
        try container.encode(array, forKey: .array)
        try container.encodeIfPresent(optionalDict, forKey: .optionalDict)
        try container.encodeIfPresent(optionalArray, forKey: .optionalArray)
    }
}

Details

Xcode 12.0.1 (12A7300)

Swift 5.3

Based on Tai Le library

// code from: https://github.com/levantAJ/AnyCodable/blob/master/AnyCodable/DecodingContainer%2BAnyCollection.swift

private
struct AnyCodingKey: CodingKey {
    let stringValue: String
    private (set) var intValue: Int?
    init?(stringValue: String) { self.stringValue = stringValue }
    init?(intValue: Int) {
        self.intValue = intValue
        stringValue = String(intValue)
    }
}

extension KeyedDecodingContainer {

    private
    func decode(_ type: [Any].Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> [Any] {
        var values = try nestedUnkeyedContainer(forKey: key)
        return try values.decode(type)
    }

    private
    func decode(_ type: [String: Any].Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> [String: Any] {
        try nestedContainer(keyedBy: AnyCodingKey.self, forKey: key).decode(type)
    }

    func decode(_ type: [String: Any].Type) throws -> [String: Any] {
        var dictionary: [String: Any] = [:]
        for key in allKeys {
            if try decodeNil(forKey: key) {
                dictionary[key.stringValue] = NSNull()
            } else if let bool = try? decode(Bool.self, forKey: key) {
                dictionary[key.stringValue] = bool
            } else if let string = try? decode(String.self, forKey: key) {
                dictionary[key.stringValue] = string
            } else if let int = try? decode(Int.self, forKey: key) {
                dictionary[key.stringValue] = int
            } else if let double = try? decode(Double.self, forKey: key) {
                dictionary[key.stringValue] = double
            } else if let dict = try? decode([String: Any].self, forKey: key) {
                dictionary[key.stringValue] = dict
            } else if let array = try? decode([Any].self, forKey: key) {
                dictionary[key.stringValue] = array
            }
        }
        return dictionary
    }
}

extension UnkeyedDecodingContainer {
    mutating func decode(_ type: [Any].Type) throws -> [Any] {
        var elements: [Any] = []
        while !isAtEnd {
            if try decodeNil() {
                elements.append(NSNull())
            } else if let int = try? decode(Int.self) {
                elements.append(int)
            } else if let bool = try? decode(Bool.self) {
                elements.append(bool)
            } else if let double = try? decode(Double.self) {
                elements.append(double)
            } else if let string = try? decode(String.self) {
                elements.append(string)
            } else if let values = try? nestedContainer(keyedBy: AnyCodingKey.self),
                let element = try? values.decode([String: Any].self) {
                elements.append(element)
            } else if var values = try? nestedUnkeyedContainer(),
                let element = try? values.decode([Any].self) {
                elements.append(element)
            }
        }
        return elements
    }
}

Solution

struct DecodableDictionary: Decodable {
    typealias Value = [String: Any]
    let dictionary: Value?
    init(from decoder: Decoder) throws {
        dictionary = try? decoder.container(keyedBy: AnyCodingKey.self).decode(Value.self)
    }
}

Usage

struct Model: Decodable {
    let num: Double?
    let flag: Bool?
    let dict: DecodableDictionary?
    let dict2: DecodableDictionary?
    let dict3: DecodableDictionary?
}

let data = try! JSONSerialization.data(withJSONObject: dictionary)
let object = try JSONDecoder().decode(Model.self, from: data)
print(object.dict?.dictionary)      // prints [String: Any]
print(object.dict2?.dictionary)     // prints nil
print(object.dict3?.dictionary)     // prints nil

decode using decoder and coding keys

public let dataToDecode: [String: AnyDecodable]

enum CodingKeys: CodingKey {
    case dataToDecode
}

init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.dataToDecode = try container.decode(Dictionary<String, AnyDecodable>.self, forKey: .dataToDecode) 
}    

I used some of the answers on this topic to get the simplest solution possible for me. My problem is that I was receiving a [String: Any] type dictionary, but I could very well work with a [String: String] transforming every other Any value in String. So this is my solution:

struct MetadataType: Codable {
    let value: String?

    private init(_ value: String?) {
        self.value = value
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()

        if let decodedValue = try? container.decode(Int.self) {
            self.init(String(decodedValue))
        } else if let decodedValue = try? container.decode(Double.self) {
            self.init(String(decodedValue))
        } else if let decodedValue = try? container.decode(Bool.self) {
            self.init(String(decodedValue))
        } else if let decodedValue = try? container.decode(String.self) {
            self.init(decodedValue)
        } else {
            self.init(nil)
        }
    }
}

And when declaring my dictionary, I use

let userInfo: [String: MetadataType]

The easiest and suggested way is to create separate model for each dictionary or model that is in JSON.

Here is what I do

//Model for dictionary **Metadata**

struct Metadata: Codable {
    var link_id: String?
    var buy_count: Int?
}  

//Model for dictionary **Customer**

struct Customer: Codable {
   var object: String?
   var id: String?
   var email: String?
   var metadata: Metadata?
}

//Here is our decodable parser that decodes JSON into expected model

struct CustomerParser {
    var customer: Customer?
}

extension CustomerParser: Decodable {

//keys that matches exactly with JSON
enum CustomerKeys: String, CodingKey {
    case object = "object"
    case id = "id"
    case email = "email"
    case metadata = "metadata"
}

init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CustomerKeys.self) // defining our (keyed) container

    let object: String = try container.decode(String.self, forKey: .object) // extracting the data
    let id: String = try container.decode(String.self, forKey: .id) // extracting the data
    let email: String = try container.decode(String.self, forKey: .email) // extracting the data

   //Here I have used metadata model instead of dictionary [String: Any]
    let metadata: Metadata = try container.decode(Metadata.self, forKey: .metadata) // extracting the data

    self.init(customer: Customer(object: object, id: id, email: email, metadata: metadata))

    }
}

Usage:

  if let url = Bundle.main.url(forResource: "customer-json-file", withExtension: "json") {
        do {
            let jsonData: Data =  try Data(contentsOf: url)
            let parser: CustomerParser = try JSONDecoder().decode(CustomerParser.self, from: jsonData)
            print(parser.customer ?? "null")

        } catch {

        }
    }

**I have used optional to be in safe side while parsing, can be changed as needed.

Read more on this topic

This will work

public struct AnyDecodable: Decodable {
    public let value: Any

    public init<T>(_ value: T?) {
        self.value = value ?? ()
    }
}

let contentDecodable = try values.decodeIfPresent(AnyDecodable.self, forKey: .content)

extension ViewController {

    func swiftyJson(){
        let url = URL(string: "https://itunes.apple.com/search?term=jack+johnson")
        //let url = URL(string: "http://makani.bitstaging.in/api/business/businesses_list")

        Alamofire.request(url!, method: .get, parameters: nil).responseJSON { response in
            var arrayIndexes = [IndexPath]()
            switch(response.result) {
            case .success(_):

                let data = response.result.value as! [String : Any]

                if let responseData =  Mapper<DataModel>().map(JSON: data) {
                    if responseData.results!.count > 0{
                        self.arrayExploreStylistList = []
                    }
                    for i in 0..<responseData.results!.count{
                        arrayIndexes.append(IndexPath(row: self.arrayExploreStylistList.count + i, section: 0))
                    }
                    self.arrayExploreStylistList.append(contentsOf: responseData.results!)

                    print(arrayIndexes.count)

                }

                //                    if let arrNew = data["results"] as? [[String : Any]]{
                //                        let jobData = Mapper<DataModel>().mapArray(JSONArray: arrNew)
                //                        print(jobData)
                //                        self.datamodel = jobData
                //                    }
                self.tblView.reloadData()
                break

            case .failure(_):
                print(response.result.error as Any)
                break

            }
        }

    }
}