JSONCodable: A Swift repository from lucatorella

#JSONCodable Hassle-free JSON encoding and decoding in Swift

Installation

Simply add the following to your Cartfile:

github "matthewcheok/JSONCodable"

and then run carthage update

Swift 2.0 Required This project uses a variety of Swift features including Protocol Extensions and Error Handling available in Swift 2.0

Breaking Change JSONCodable now supports let properties. You now implement init?(JSONDictionary: [String:AnyObject]) instead of func JSONDecode() and func toJSON() instead of func JSONEncode().

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 {
        var result: [String: AnyObject] = [:]
        try result.encode(id, key: "id")
        try result.encode(name, key: "full_name")
        try result.encode(email, key: "email")
        try result.encode(company, key: "company")
        try result.encode(friends, key: "friends")
        return result
    }
}

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?(JSONDictionary: [String:AnyObject]) {
        do {
            id = try JSONDictionary.decode("id")
            name = try JSONDictionary.decode("full_name")
            email = try JSONDictionary.decode("email")
            company = try JSONDictionary.decode("company")
            friends = try JSONDictionary.decode("friends")
        }
        catch {
            print(error)
            return nil
        }
    }
}

extension Company: JSONDecodable {
    init?(JSONDictionary: [String:AnyObject]) {
        do {
            name = try JSONDictionary.decode("name")
            address = try JSONDictionary.decode("address")
        }
        catch {
            print(error)
            return nil
        }
    }
}

Simply provide the implementations for init?(JSONDictionary: [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 = User(JSONDictionary: 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?(JSONDictionary: [String : AnyObject]) {
    do {
        ...
        website = try JSONDictionary.decode("website", transformer: JSONTransformerStringToNSURL)
    }
    ...
}

func toJSON() throws -> AnyObject {
    var result = [String: AnyObject]()
    ...
    try result.encode(website, key: "website", transformer: JSONTransformerStringToNSURL)
    return result
}

The following transformers are provided by default:

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

Feel free to suggest more!

Example code

Refer to the Demo project in the workspace for more information. You might experience issues executing the playground in Xcode 7.0 Beta.

License