Code Quality Rank: L4
Programming language: Swift
License: MIT License
Tags: Data Management     JSON    
Latest version: v3.2.1

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Welcome to Genome 3.0. This library seeks to satisfy the following goals:

  • [x] Data Type Agnostic
  • [x] Failure Driven
  • [x] Nested Mapping
  • [x] Collection Mapping
  • [x] Simple and Consistent
  • [x] Two-Way Serialization
  • [x] Transforms
  • [x] Type Safety
  • [x] Constants (let)
  • [x] Full Linux Support
  • [x] Struct Friendly
  • [x] Inheritance Friendly
  • [x] Core Data and Persistence Compatible


Genome is built on top of Node as opposed to JSON directly. This makes it easy for Genome to work with any data type through little effort.

All mapping operations are built as sugar on top of Node's core.

Optimized For JSON

Works great w/ JSON out of the box by default:

let task = URLSession.shared.dataTask(with: url) { data, response, error in
    guard let data = data else { return }
    do {
        let model = try Model(node: data)
    } catch {

If your data is nested, you can use Node to take it further.

let json = try rawJSONData.makeNode()
guard let items = json["root", "items"] else { return }
let models = try [Item](node: items)

You'll notice above that we used initialized an array, this is all perfectly great w/ Genome.

If you're working on Linux with SwiftPM, it is highly recommended to use a type-safe JSON library like this one.


We can create our JSON Data the same way:

let jsonData = try Data(node: item)
api.post(jsonData) { response in ... }

Building Project

All future development of Cocoapods will be done on with SwiftPM. Cocoapods and Carthage support are intended to be maintained, but are not used in development. Here are some useful commands

# make xcode project
swift package generate-xcodeproj
# build project
swift build
# test project
swift test


To use SwiftPM, add this to your Package.swift

.Package(url: "https://github.com/LoganWright/Genome.git", majorVersion: 3)


pod 'Genome', '~> 3.0'


github "LoganWright/Genome"

Table Of Contents

Quick Start

Let's take the following hypothetical JSON

    "name" : "Rover",
    "nickname" : "RoRo", // Optional Value
    "type" : "dog"

Here's how we might create the model for this

enum PetType: String {
    case dog
    case cat
    case unknown

struct Pet: MappableObject {
    let name: String
    let type: PetType
    let nickname: String?

    init(map: Map) throws {
        name = try map.extract("name")
        nickname = try map.extract("nickname")
        type = try map.extract("type") { PetType(rawValue: $0) ?? .unknown }

    func sequence(map: Map) throws {
        try name ~> map["name"]
        try type ~> map["type"].transformToNode { $0.rawValue }
        try nickname ~> map["nickname"]

Once that's done, we can build like so:

let pet = try Pet(node: json)

It will also work with collections:

let pets = try [Pet](node: jsonArray)

NASA Photo

Let's build a simple example that fetches NASA's photo of the day. Please note that this is a synchronous API, and it makes use of Data for brevity. It is advisable to use an asynchronous and proper HTTP Client like URLSession.

struct Photo: BasicMappable {
    private(set) var title: String = ""
    private(set) var mediaType: String = ""
    private(set) var explanation: String = ""
    private(set) var concepts: [String] = []

    private(set) var imageUrl: NSURL!

    mutating func sequence(_ map: Map) throws {
        try title <~ map["title"]
        try mediaType <~ map ["media_type"]
        try explanation <~ map["explanation"]
        try concepts <~ map["concepts"]
        try imageUrl <~ map["url"]
            .transformFromNode { NSURL(string: $0) }

struct NASA {
    static let url = URL(string: "https://api.nasa.gov/planetary/apod?concept_tags=True&api_key=DEMO_KEY")!

    static func fetchPhoto() throws -> Photo {
        let data = try Data(contentsOf: NASA.url)
        return try Photo(node: data)

Now we can call like this:

let photo = try NASA.fetchPhoto()

WARNING: Please read first paragraph regarding synchronicity and api.


This is one of the core protocol options for this library. It will be the go to for most standard mapping operations.

It has two requirements

init(map: Map) throws

This is the initializer you will use to map your object. You may call this manually if you like, but if you use any of the built in convenience initializers, this will be called automatically. Otherwise, if you need to initialize a Map, use:

let map = Map(node: someNode, in: someContext)

It has two main requirements

sequence(map: Map) throws

The sequence function is called in two main situations. It is marked mutating because it will modify values on fromNode operations. If however, you're only using sequence for toNode, nothing will be mutated and one can remove the mutating keyword. (as in the above example)


When mapping to Node w/ any of the convenience initializer. After instantiating the object, sequence will be called. This allows objects that don't initialize constants or objects that use the two-way operator to complete their mapping.

If you are initializing w/ init(map: Map) directly, you will be responsible for calling sequence manually if your object requires it.

It is marked mutating because it will modify values.

Note, if you're only mapping to Node, nothing will be mutated.


When accessing an objects makeNode(), the sequence operation will be called to collect the values into a Node package.


This is one of the main operations used in this library. The ~ symbolizes a connection, and the < and > respectively symbol a flow of value. When declared as ~> it symbolizes that mapping only happens from value, to Node.

You could also use the following:

Operator Directions Example Mutates
<~> To and From Node try name <~> map["name"] โœ“
~> To Node Only try clientId ~> map["client_id"] ๐˜…
<~ From Node Only try updatedAt <~ map["updated_at"] โœ“


Genome provides various options for transforming values. These are type-safe and will be checked by the compiler.

These are chainable, like the following:

try type <~> map["type"]
    .transformFromNode {
        return PetType(rawValue: $0)
    .transformToNode {
        return $0.rawValue

Note: At the moment, transforms require absolute optionality conformance in some situations. ie, Optionals get Optionals, ImplicitlyUnwrappedOptionals get ImplicitlyUnwrappedOptionals, etc.


When using let constants, you will need to call a transformer that sets the value instantly. In this case, you will call fromNode and pass any closure that takes a NodeConvertibleType (a standard Node type) and returns a value.


Use this if you need to transform the node input to accomodate your type. In our example above, we need to convert the raw node to our associated enum. This can also be appended to mappings for the <~ operator.


Use this if you need to transform the given value to something more suitable for data. This can also be appended to mappings for the ~> operator.


Why is the try keyword on every line! Every mapping operation is failable if not properly specified. It's better to deal with these possibilities, head first.

For example, if the property being set is non-optional, and nil is found in the Node, the operation should throw an error that can be easily caught.

More Concepts

Some of the different functionality available in Genome

The way that Genome is constructed, you should never have to deal w/ Node beyond deserializing and serializing for your web services. It can still be used directly if desired.


Genome is most suited to final classes and structures, but it does support Inheritance. Unfortunately, due to some limitations surrounding generics, protocols, and Self it requires some extra effort.


The Object type is provided by the library to satisfy most inheritance based mapping operations. Simply subclass Object and you're good to go:

class MyClass : Object {}

Note: If you're using Realm, or another library that has also used Object, don't forget that these are module namespaced in Swift. If that's the case, you should declare your class: class MyClass : Genome.Object {}


In order to support flexible customization, Genome provides various mapping options for protocols. Your object can conform to any of the following. Although each of these initializers is marked with throws, it is not necessary for your initializer to throw if it is guaranteed to succeed. In that case, you can omit the throws keyword safely.

Protocol Required Initializer
BasicMappable init() throws
MappableObject init(map: Map) throws

These are all just convenience protocols, and ultimately all derive from MappableBase. If you wish to define your own implementation, the rest of the library's functionality will still apply.


This is the true root of the library. Even MappableBase mentioned above inherits from this core type. It has two requirements:

public protocol NodeConvertibleType {
    init(node: Node, in context: Context) throws
    func makeNode(context: Context) throws -> Node

All basic types such as Int, String, etc. conform to this protocol which allows ultimate flexibility in defining the library. It also paves the way to much fewer overloads going forward when collections of NodeConvertible can also conform to it.


If you are using the standard instantiation scheme established in the library, you will likely initialize with this function.

public init(node: Node, in context: Context = EmptyNode) throws

Now we can easily create an object safely:

do {
    let rover = try Pet(node: nodeRover)
} catch {

If all we care about is whether or not we were able to create an object, we can also do the following:

let rover = try? Pet(node: nodeRover)
print(rover) // Rover is type: `Pet?`


Context is defined as an empty protocol that any object you might need access to can conform to and passed within.


If you're using Foundation, you can transform Any, [String: Any], and [Any] types by making them into a Node first. Node(any: yourTypeHere).


You can instantiate collections directly w/o mapping as well:

let people = try [People](node: someNode)

Core Data

If you wish to use CoreData, instead of subclassing NSManagedObject, subclass ManagedObject.

Happy Mapping!