zadr/j2s

A macOS app to convert JSON to Swift structs

What's this?

j2s is a macOS app that converts JSON dictionaries into Swift structs.

That's it? Can I make it do anything else?

No, yeah, that's it. You give j2s a json file, and it gives you Swift structs. You can pick if it outputs to one file or a n files for n structs.

If you want to make it do anything else, you'll have to write some more code. I'll probably accept pull requests, but, you should probably look into other tools like Sourcery instead.

Codable-compliant structs, right?

Yup.

Cool

Yeah. j2s will also convert snake_case_key_names into camelCasePropertyNames, and if you have a key where the value is an array of of dictionaries, the key name will be — naively — depluralized (exact line of code may change, but look around there for the algorithm).

And, if your JSON value is a string that's secretly a Date in a format that j2s understands (Currently: ISO8601), the generated code will use the correct (Date) type.

Also, an integer like 5 is an Int and a floating point number like 5.0 is a Double. Because, you know, thats how these things should work.

What version of Swift does this target?

j2s.xcodeproj requires Swift 4 (Xcode 9 or greater) to build. The code it outputs requires Swift 4. If you need Swift 3 support, try looking back in commit history for an older version.

What's the generated code look like?

j2s can take in the following JSON:

{
  "outer" : true,
  "nested" : {
    "what_if_i_want_to" : [
      "boogie? wouldn't dream of stopping you"
    ],
    "when" : "2017-06-27T17:58:28+00:00",
    "cool" : true
  }
}

and turn it into Swift code that looks like this:

public struct Root: Codable {
	public let nested: Nested
	public let outer: Bool

	public struct Nested: Codable {
		public let cool: Bool
		public let whatIfIWantTo: [String]
		public let when: Date
		}
}

// MARK: -

public extension Root {
	static func create(with data: Data) throws -> Root  {
		return try JSONDecoder().decode(Root.self, from: data)
	}

	static func create(with data: Data) throws -> [Root]  {
		return try JSONDecoder().decode([Root].self, from: data)
	}
}

// MARK: -

public extension Root.Nested {
	static func create(with data: Data) throws -> Root.Nested  {
		let decoder = JSONDecoder()
		decoder.dateDecodingStrategy = .iso8601
		return try decoder.decode(Root.Nested.self, from: data)
	}

	static func create(with data: Data) throws -> [Root.Nested]  {
		let decoder = JSONDecoder()
		decoder.dateDecodingStrategy = .iso8601
		return try decoder.decode([Root.Nested].self, from: data)
	}
}

What about Optionals? I heard Swift has Optionals, but, I don't see any Optionals.

Optionals are sort of handled by j2s. JSON doesn't have Optionals, so it's hard to map them over automatically.

While parsing, if j2s is told to create the same struct multiple times, it considers any properties that don't exist in both models to be Optional.

The same is also true for properties that show up as null and as a Type.

nulls are turned into Any?.

Oh.

Yeah. Usually happens in the case of an array of dictionaries. This JSON:

{
  "outer" : true,
  "nested" : {
    "im_going_to_" : [
      "type? sure, but uncheck the \"Pretty-Print JSON\" box down there --v",
      "boogie? wouldn't dream of stopping you"
    ],
    "what" : "paste json here"
  }
}

will generate this Swift code:

public struct Demo: Codable {
	public let nested: Nested
	public let outer: Bool

	public struct Nested: Codable {
		public let imGoingTo: [String]
		public let what: String
	}
}

// MARK: -

public extension Nested {
	public static func create(with data: Data) throws -> Nested  {
		return try JSONDecoder().decode(Nested.self, from: data)
	}

	public static func create(with data: Data) throws -> [Nested]  {
		return try JSONDecoder().decode([Nested].self, from: data)
	}
}

// MARK: -

public extension Demo {
	public static func create(with data: Data) throws -> Demo  {
		return try JSONDecoder().decode(Demo.self, from: data)
	}

	public static func create(with data: Data) throws -> [Demo]  {
		return try JSONDecoder().decode([Demo].self, from: data)
	}
}

Why build this and not use some other tool?

Seemed like a good idea. This was before Codable was a thing.

Still hung up on depluralization? (Singularity?)

A JSON dictionary with a key named potatoes, where the value is a list of dictionaries will be given the Swift type [Potato]. Similarly, soliloquies becomes [Soliloquy], dwarves and [Dwarf], and so on. Depluralization is a giant if statement though, so while indices becomes [Index], matrices incorrectly becomes matrex. If Anyone wanted to do some natural language processing to solve this, that would be cool.

Okay then

Before you go, remember that j2s code is released under a 2-Clause BSD License and all contributions and project activity should be in line with our Code of Conduct.