ObjectMapper is a framework written in Swift that makes it easy for you to convert your model objects (classes and structs) to and from JSON.
- Features
- The Basics
- Mapping Nested Objects
- Custom Transformations
- Subclassing
- Generic Objects
- Mapping Context
- ObjectMapper + Alamofire
- ObjectMapper + Realm
- Projects using ObjectMapper
- To Do
- Contributing
- Installation
- Mapping JSON to objects
- Mapping objects to JSON
- Nested Objects (stand alone, in arrays or in dictionaries)
- Custom transformations during mapping
- Struct support
- Immutable support
To support mapping, a class or struct just needs to implement the Mappable
protocol which includes the following functions:
init?(map: Map)
mutating func mapping(map: Map)
ObjectMapper uses the <-
operator to define how each member variable maps to and from JSON.
class User: Mappable {
var username: String?
var age: Int?
var weight: Double!
var array: [Any]?
var dictionary: [String : Any] = [:]
var bestFriend: User? // Nested User object
var friends: [User]? // Array of Users
var birthday: Date?
required init?(map: Map) {
}
// Mappable
func mapping(map: Map) {
username <- map["username"]
age <- map["age"]
weight <- map["weight"]
array <- map["arr"]
dictionary <- map["dict"]
bestFriend <- map["best_friend"]
friends <- map["friends"]
birthday <- (map["birthday"], DateTransform())
}
}
struct Temperature: Mappable {
var celsius: Double?
var fahrenheit: Double?
init?(map: Map) {
}
mutating func mapping(map: Map) {
celsius <- map["celsius"]
fahrenheit <- map["fahrenheit"]
}
}
Once your class implements Mappable
, ObjectMapper allows you to easily convert to and from JSON.
Convert a JSON string to a model object:
let user = User(JSONString: JSONString)
Convert a model object to a JSON string:
let JSONString = user.toJSONString(prettyPrint: true)
Alternatively, the Mapper.swift
class can also be used to accomplish the above (it also provides extra functionality for other situations):
// Convert JSON String to Model
let user = Mapper<User>().map(JSONString: JSONString)
// Create JSON String from Model
let JSONString = Mapper().toJSONString(user, prettyPrint: true)
ObjectMapper can map classes composed of the following types:
Int
Bool
Double
Float
String
RawRepresentable
(Enums)Array<Any>
Dictionary<String, Any>
Object<T: Mappable>
Array<T: Mappable>
Array<Array<T: Mappable>>
Set<T: Mappable>
Dictionary<String, T: Mappable>
Dictionary<String, Array<T: Mappable>>
- Optionals of all the above
- Implicitly Unwrapped Optionals of the above
This function is where all mapping definitions should go. When parsing JSON, this function is executed after successful object creation. When generating JSON, it is the only function that is called on the object.
This failable initializer is used by ObjectMapper for object creation. It can be used by developers to validate JSON prior to object serialization. Returning nil within the function will prevent the mapping from occuring. You can inspect the JSON stored within the Map
object to do your validation:
required init?(map: Map){
// check if a required "name" property exists within the JSON.
if map.JSON["name"] == nil {
return nil
}
}
StaticMappable
is an alternative to Mappable
. It provides developers with a static function that is used by ObjectMapper for object initialization instead of init?(map: Map)
.
Note: StaticMappable
, like Mappable
, is a sub protocol of BaseMappable
which is where the mapping(map: Map)
function is defined.
ObjectMapper uses this function to get objects to use for mapping. Developers should return an instance of an object that conforms to BaseMappable
in this function. This function can also be used to:
- validate JSON prior to object serialization
- provide an existing cached object to be used for mapping
- return an object of another type (which also conforms to
BaseMappable
) to be used for mapping. For instance, you may inspect the JSON to infer the type of object that should be used for mapping (see examples in ClassClusterTests.swift)
If you need to implement ObjectMapper in an extension, you will need to adopt this protocol instead of Mappable
.
ImmutableMappable
provides the ability to map immutable properties. This is how ImmutableMappable
differs from Mappable
:
ImmutableMappable | Mappable |
---|---|
Properties | |
let id: Int let name: String? |
var id: Int! var name: String? |
JSON -> Model | |
init(map: Map) throws { id = try map.value("id") name = try? map.value("name") } |
mutating func mapping(map: Map) { id <- map["id"] name <- map["name"] } |
Model -> JSON | |
func mapping(map: Map) { id >>> map["id"] name >>> map["name"] } |
mutating func mapping(map: Map) { id <- map["id"] name <- map["name"] } |
Initializing | |
try User(JSONString: JSONString) |
User(JSONString: JSONString) |
This throwable initializer is used to map immutable properties from the given Map
. Every immutable property should be initialized in this initializer.
This initializer throws an error when:
Map
fails to get a value for the given keyMap
fails to transform a value usingTransform
ImmutableMappable
uses Map.value(_:using:)
method to get values from the Map
. This method should be used with the try
keyword as it is throwable. Optional
properties can easily be handled using try?
.
init(map: Map) throws {
name = try map.value("name") // throws an error when it fails
createdAt = try map.value("createdAt", using: DateTransform()) // throws an error when it fails
updatedAt = try? map.value("updatedAt", using: DateTransform()) // optional
posts = (try? map.value("posts")) ?? [] // optional + default value
surname = try? map.value("surname", default: "DefaultSurname") // optional + default value as an argument
}
This method is where the reverse transform is performed (model to JSON). Since immutable properties cannot be mapped with the <-
operator, developers have to define the reverse transform using the >>>
operator.
mutating func mapping(map: Map) {
name >>> map["name"]
createdAt >>> (map["createdAt"], DateTransform())
updatedAt >>> (map["updatedAt"], DateTransform())
posts >>> map["posts"]
}
ObjectMapper supports dot notation within keys for easy mapping of nested objects. Given the following JSON String:
"distance" : {
"text" : "102 ft",
"value" : 31
}
You can access the nested objects as follows:
func mapping(map: Map) {
distance <- map["distance.value"]
}
Nested keys also support accessing values from an array. Given a JSON response with an array of distances, the value could be accessed as follows:
distance <- map["distances.0.value"]
If you have a key that contains .
, you can individually disable the above feature as follows:
func mapping(map: Map) {
identifier <- map["app.identifier", nested: false]
}
When you have nested keys which contain .
, you can pass the custom nested key delimiter as follows (#629):
func mapping(map: Map) {
appName <- map["com.myapp.info->com.myapp.name", delimiter: "->"]
}
ObjectMapper also supports custom transforms that convert values during the mapping process. To use a transform, simply create a tuple with map["field_name"]
and the transform of your choice on the right side of the <-
operator:
birthday <- (map["birthday"], DateTransform())
The above transform will convert the JSON Int value to an Date when reading JSON and will convert the Date to an Int when converting objects to JSON.
You can easily create your own custom transforms by adopting and implementing the methods in the TransformType
protocol:
public protocol TransformType {
associatedtype Object
associatedtype JSON
func transformFromJSON(_ value: Any?) -> Object?
func transformToJSON(_ value: Object?) -> JSON?
}
In a lot of situations you can use the built-in transform class TransformOf
to quickly perform a desired transformation. TransformOf
is initialized with two types and two closures. The types define what the transform is converting to and from and the closures perform the actual transformation.
For example, if you want to transform a JSON String
value to an Int
you could use TransformOf
as follows:
let transform = TransformOf<Int, String>(fromJSON: { (value: String?) -> Int? in
// transform value from String? to Int?
return Int(value!)
}, toJSON: { (value: Int?) -> String? in
// transform value from Int? to String?
if let value = value {
return String(value)
}
return nil
})
id <- (map["id"], transform)
Here is a more condensed version of the above:
id <- (map["id"], TransformOf<Int, String>(fromJSON: { Int($0!) }, toJSON: { $0.map { String($0) } }))
Classes that implement the Mappable
protocol can easily be subclassed. When subclassing mappable classes, follow the structure below:
class Base: Mappable {
var base: String?
required init?(map: Map) {
}
func mapping(map: Map) {
base <- map["base"]
}
}
class Subclass: Base {
var sub: String?
required init?(map: Map) {
super.init(map)
}
override func mapping(map: Map) {
super.mapping(map)
sub <- map["sub"]
}
}
Make sure your subclass implementation calls the right initializers and mapping functions to also apply the mappings from your superclass.
ObjectMapper can handle classes with generic types as long as the generic type also conforms to Mappable
. See the following example:
class Result<T: Mappable>: Mappable {
var result: T?
required init?(map: Map){
}
func mapping(map: Map) {
result <- map["result"]
}
}
let result = Mapper<Result<User>>().map(JSON)
The Map
object which is passed around during mapping, has an optional MapContext
object that is available for developers to use if they need to pass information around during mapping.
To take advantage of this feature, simply create an object that implements MapContext
(which is an empty protocol) and pass it into Mapper
during initialization.
struct Context: MapContext {
var importantMappingInfo = "Info that I need during mapping"
}
class User: Mappable {
var name: String?
required init?(map: Map){
}
func mapping(map: Map){
if let context = map.context as? Context {
// use context to make decisions about mapping
}
}
}
let context = Context()
let user = Mapper<User>(context: context).map(JSONString)
If you are using Alamofire for networking and you want to convert your responses to Swift objects, you can use AlamofireObjectMapper. It is a simple Alamofire extension that uses ObjectMapper to automatically map JSON response data to Swift objects.
ObjectMapper and Realm can be used together. Simply follow the class structure below and you will be able to use ObjectMapper to generate your Realm models:
class Model: Object, Mappable {
dynamic var name = ""
required convenience init?(map: Map) {
self.init()
}
func mapping(map: Map) {
name <- map["name"]
}
}
If you want to serialize associated RealmObjects, you can use ObjectMapper+Realm. It is a simple Realm extension that serializes arbitrary JSON into Realm's List
class.
To serialize Swift String
, Int
, Double
and Bool
arrays you can use ObjectMapperAdditions/Realm. It'll wrap Swift types into RealmValues that can be stored in Realm's List
class.
Note: Generating a JSON string of a Realm Object using ObjectMappers' toJSON
function only works within a Realm write transaction. This is because ObjectMapper uses the inout
flag in its mapping functions (<-
) which are used both for serializing and deserializing. Realm detects the flag and forces the toJSON
function to be called within a write block even though the objects are not being modified.
-
Xcode Plugin for generating
Mappable
andImmutableMappable
code -
Json4Swift - Supports generating
ImmutableMappable
structs online (no plugins needed) -
JSON to Model - Template based MacOS app which generates structs with customisation. ⬇️Download App
If you have a project that utilizes, extends or provides tooling for ObjectMapper, please submit a PR with a link to your project in this section of the README.
- Improve error handling. Perhaps using
throws
- Class cluster documentation
Contributions are very welcome 👍😃.
Before submitting any pull request, please ensure you have run the included tests and they have passed. If you are including new functionality, please write test cases for it as well.
ObjectMapper can be added to your project using CocoaPods 0.36 or later by adding the following line to your Podfile
:
pod 'ObjectMapper', '~> 3.5' (check releases to make sure this is the latest version)
If you're using Carthage you can add a dependency on ObjectMapper by adding it to your Cartfile
:
github "tristanhimmelman/ObjectMapper" ~> 3.5 (check releases to make sure this is the latest version)
To add ObjectMapper to a Swift Package Manager based project, add:
.package(url: "https://github.com/tristanhimmelman/ObjectMapper.git", .upToNextMajor(from: "4.1.0")),
to your Package.swift
files dependencies
array.
Otherwise, ObjectMapper can be added as a submodule:
- Add ObjectMapper as a submodule by opening the terminal,
cd
-ing into your top-level project directory, and entering the commandgit submodule add https://github.com/tristanhimmelman/ObjectMapper.git
- Open the
ObjectMapper
folder, and dragObjectMapper.xcodeproj
into the file navigator of your app project. - In Xcode, navigate to the target configuration window by clicking on the blue project icon, and selecting the application target under the "Targets" heading in the sidebar.
- Ensure that the deployment target of
ObjectMapper.framework
matches that of the application target. - In the tab bar at the top of that window, open the "Build Phases" panel.
- Expand the "Target Dependencies" group, and add
ObjectMapper.framework
. - Click on the
+
button at the top left of the panel and select "New Copy Files Phase". Rename this new phase to "Copy Frameworks", set the "Destination" to "Frameworks", and addObjectMapper.framework
.