#JSONCodable Hassle-free JSON encoding and decoding in Swift

Installation

• Simply add the following to your Cartfile and run carthage update:

github "matthewcheok/JSONCodable" ~> 2.1

• or add the following to your Podfile and run pod install:

pod 'JSONCodable', '~> 2.1'

• or clone as a git submodule,

• or just copy files in the JSONCodable folder into your project.

TLDR

• Uses Protocol Extensions
• Error Handling
• Supports let properties
• Supports enum properties backed by compatible values

Change Log

• Moved encoding and decoding methods to a helper class

---

JSONCodable is made of two separate protocols JSONEncodable and JSONDecodable. JSONEncodable allows your structs and classes to generate NSDictionary or [String: AnyObject] equivalents for use with NSJSONSerialization. JSONDecodable allows you to generate structs from NSDictionary coming in from a network request for example.

We'll use the following models in this example:

struct User {
    let id: Int
    let name: String
    var email: String?
    var company: Company?
    var friends: [User] = []
}

struct Company {
    let name: String
    var address: String?
}

Using JSONEncodable

Simply add conformance to JSONEncodable (or to JSONCodable):

extension User: JSONEncodable {
    func toJSON() throws -> AnyObject {
        return try JSONEncoder.create({ (encoder) -> Void in
            try encoder.encode(id, key: "id")
            try encoder.encode(name, key: "full_name")
            try encoder.encode(email, key: "email")
            try encoder.encode(company, key: "company")
            try encoder.encode(friends, key: "friends")
        })
    }
}

extension Company: JSONEncodable {}

The default implementation of func toJSON() inspects the properties of your type using reflection (see Company.) If you need a different mapping, you can provide your own implementation (see User.)

Instantiate your struct, then use the func toJSON() method to obtain a equivalent form suitable for use with NSJSONSerialization:

let dict = try user.toJSON()
print("dict: \(dict)")

Result:

[full_name: John Appleseed, id: 24, email: john@appleseed.com, company: {
    address = "1 Infinite Loop, Cupertino, CA";
    name = Apple;
}, friends: (
        {
        friends =         (
        );
        "full_name" = "Bob Jefferson";
        id = 27;
    },
        {
        friends =         (
        );
        "full_name" = "Jen Jackson";
        id = 29;
    }
)]

##Using JSONDecodable

Simply add conformance to JSONDecodable (or to JSONCodable):

extension User: JSONDecodable {
  init(object: JSONObject) throws {
      let decoder = JSONDecoder(object: object)        
      id = try decoder.decode("id")
      name = try decoder.decode("full_name")
      email = try decoder.decode("email")
      company = try decoder.decode("company")
      friends = try decoder.decode("friends")
  }
}

extension Company: JSONDecodable {
  init(object: JSONObject) throws {
      let decoder = JSONDecoder(object: object)
      name = try decoder.decode("name")
      address = try decoder.decode("address")
  }
}

Simply provide the implementations for init(object: JSONObject) throws where JSONObject is a typealias for [String:AnyObject]. As before, you can use this to configure the mapping between keys in the Dictionary to properties in your structs and classes.

let user = try! User(object: JSON)
print("\(user)")

Result:

User(
  id: 24,
  name: "John Appleseed",
  email: Optional("john@appleseed.com"),
  company: Optional(Company(
    name: "Apple",
    address: Optional("1 Infinite Loop, Cupertino, CA")
  )),
  friends: [
    User(
      id: 27,
      name: "Bob Jefferson",
      email: nil,
      company: nil,
      friends: []
    ),
    User(
      id: 29,
      name: "Jen Jackson",
      email: nil,
      company: nil,
      friends: []
    )
  ]
)

Working with JSON Strings

The convenience initializer init?(JSONString: String) is provided on JSONDecodable. You may also use func toJSONString() throws -> String to obtain a string equivalent of your types.

Transforming values

To transform values, create an instance of JSONTransformer:

let JSONTransformerStringToNSURL = JSONTransformer<String, NSURL>(
        decoding: {NSURL(string: $0)},
        encoding: {$0.absoluteString})

A JSONTransformer converts between 2 types, in this case, String and NSURL. It takes a closure for decoding and another for encoding, and in each case, you return an optional value of the corresponding type given an input type (you can return nil if a transformation is not possible).

Next, use the overloaded versions of func encode() and func decode() to supply the transformer:

struct User {
  ...
  var website: NSURL?
}

init(object: JSONObject) throws {
    ...
    website = try JSONDictionary.decode("website", transformer: JSONTransformerStringToNSURL)
}

func toJSON() throws -> AnyObject {
    return try JSONEncoder.create({ (encoder) -> Void in
        ...
        try result.encode(website, key: "website", transformer: JSONTransformerStringToNSURL)
    })
}

The following transformers are provided by default:

• JSONTransformers.StringToNSURL: String <-> NSURL
• JSONTransformers.StringToNSDate: String <-> NSDate ISO format

Feel free to suggest more!

Extending JSONCodable (thanks to @raylillywhite)

This allows for JSONDecoder extensions that allow the type system to better aid in decoding. For example, you could do:

extension JSONDecoder {
    public func decode(key: String) throws -> NSURL {
        return try decode(key, transformer: JSONTransformers.StringToNSURL)
    }
}

then you only need to do:

try url = decoder.decode("url")

instead of

try url = decoder.decode("url", JSONTransformers.StringToNSURL)

Example code

Refer to the included playground in the workspace for more details.

License

JSONCodable is under the MIT license.