Mapper

Mapper is a simple Swift library to convert JSON to strongly typed objects. One advantage to Mapper over some other libraries is you can have immutable properties.

Installation

With CocoaPods

use_frameworks!

pod "ModelMapper"

With Carthage

github "lyft/mapper"

Usage

Simple example:

import Mapper
// Conform to the Mappable protocol
struct User: Mappable {
  let id: String
  let photoURL: URL?

  // Implement this initializer
  init(map: Mapper) throws {
    try id = map.from("id")
    photoURL = map.optionalFrom("avatar_url")
  }
}

// Create a user!
let JSON: NSDictionary = ...
let user = User.from(JSON) // This is a 'User?'

Using with enums:

enum UserType: String {
  case Normal = "normal"
  case Admin = "admin"
}

struct User: Mappable {
  let id: String
  let type: UserType

  init(map: Mapper) throws {
    try id = map.from("id")
    try type = map.from("user_type")
  }
}

Nested Mappable objects:

struct User: Mappable {
  let id: String
  let name: String

  init(map: Mapper) throws {
    try id = map.from("id")
    try name = map.from("name")
  }
}

struct Group: Mappable {
  let id: String
  let users: [User]

  init(map: Mapper) throws {
    try id = map.from("id")
    users = map.optionalFrom("users") ?? []
  }
}

Use Convertible to transparently convert other types from JSON:

extension CLLocationCoordinate2D: Convertible {
  public static func fromMap(_ value: Any) throws -> CLLocationCoordinate2D {
    guard let location = value as? NSDictionary,
      let latitude = location["lat"] as? Double,
      let longitude = location["lng"] as? Double else
      {
         throw MapperError.convertibleError(value: value, type: [String: Double].self)
      }

      return CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
  }
}

struct Place: Mappable {
  let name: String
  let location: CLLocationCoordinate2D

  init(map: Mapper) throws {
    try name = map.from("name")
    try location = map.from("location")
  }
}

let JSON: NSDictionary = [
  "name": "Lyft HQ",
  "location": [
    "lat": 37.7603392,
    "lng": -122.41267249999999,
  ],
]

let place = Place.from(JSON)

Custom Transformations

private func extractFirstName(object: Any?) throws -> String {
  guard let fullName = object as? String else {
    throw MapperError.convertibleError(value: object, type: String.self)
  }

  let parts = fullName.characters.split { $0 == " " }.map(String.init)
  if let firstName = parts.first {
    return firstName
  }

  throw MapperError.customError(field: nil, message: "Couldn't split the string!")
}

struct User: Mappable {
  let firstName: String

  init(map: Mapper) throws {
    try firstName = map.from("name", transformation: extractFirstName)
  }
}

Parse nested or entire objects

struct User: Mappable {
  let name: String
  let JSON: AnyObject

  init(map: Mapper) throws {
    // Access the 'first' key nested in a 'name' dictionary
    try name = map.from("name.first")
    // Access the original JSON (maybe for use with a transformation)
    try JSON = map.from("")
  }
}

See the docstrings and tests for more information and examples.

Open Radars

These radars have affected the current implementation of Mapper

  • rdar://23376350 Protocol extensions with initializers do not work in extensions
  • rdar://23358609 Protocol extensions with initializers do not play well with classes
  • rdar://23226135 Can’t conform to protocols with similar generic function signatures
  • rdar://23147654 Generic functions are not differentiated by their ability to throw
  • rdar://23695200 Using the ?? operator many times is unsustainable.
  • rdar://23697280 Lazy collection elements can be evaluated multiple times.
  • rdar://23718307 Non final class with protocol extensions returning Self don’t work

License

Mapper is maintained by Lyft and released under the Apache 2.0 license. See LICENSE for details

GitHub

View Github