JsonGen generates source code files with decoders and encoders for parsing JSON into immutable Swift structs.
Features
- Generates an extension with a
decodeJson
andencodeJson
method for each struct - Works on individual
.swift
files or whole directories - Handles type aliases
- Supports primitive types, nested types and custom generic types
- Allow for custom encoders and decoders
- Allow for part of the datastructure to remain untyped
- Excelent error messages when JSON decoding fails: Improving error messages
See also the blog post: Swift + JSON with code generation
Installation
Install the latest release from NPM:
> npm install -g swift-json-gen
Also copy example/JsonGen.swift
into your own project.
This file contains some encoders and decoders for default Swift and Foundation
types.
Example
Assuming you have a file example/Blog.swift
containing one or more structs:
struct Blog {
let id: Int
let name: String
let author: String?
let needsPassword : Bool
let url: NSURL
}
To generate Json decoders based a file of structs run:
> swift-json-gen example/Blog.swift
This will generate the file
example/Blog+JsonGen.swift
with the following (truncated) content:
extension Blog {
static func decodeJson(json: AnyObject) throws -> Blog {
let decoder = try JsonDecoder(json: json)
let _id = try decoder.decode("id", decoder: Int.decodeJson)
let _name = try decoder.decode("name", decoder: String.decodeJson)
let _author = try decoder.decode("author", decoder: Optional.decodeJson(String.decodeJson))
let _needsPassword = try decoder.decode("needsPassword", decoder: Bool.decodeJson)
let _url = try decoder.decode("url", decoder: NSURL.decodeJson)
guard let
id = _id,
name = _name,
author = _author,
needsPassword = _needsPassword,
url = _url
else {
throw JsonDecodeError.StructErrors(type: "Blog", errors: decoder.errors)
}
return Blog(id: id, name: name, author: author, needsPassword: needsPassword, url: url)
}
func encodeJson() -> [String: AnyObject] {
var dict: [String: AnyObject] = [:]
dict["id"] = id.encodeJson()
dict["name"] = name.encodeJson()
dict["author"] = author.encodeJson({ $0.encodeJson() })
dict["needsPassword"] = needsPassword.encodeJson()
dict["url"] = url.encodeJson()
return dict
}
}
Usage
Include the generated YourFile+JsonGen.swift
file and the
example/JsonGen.swift
file into your project.
The generated encoder and decoder can be used in conjunction with NSJSONSerialization like so:
let inputStr = "{ \"title\": \"Hello, World!\", \"published\": true, \"author\": { \"first\": \"Tom\", \"last\": \"Lokhorst\" } }"
let inputData = inputStr.dataUsingEncoding(NSUTF8StringEncoding)!
let inputObj = try! NSJSONSerialization.JSONObjectWithData(inputData, options: [])
let blog = try! Blog.decodeJson(inputObj)
let outputObj = blog.encodeJson()
let outputData = try! NSJSONSerialization.dataWithJSONObject(outputObj, options: NSJSONWritingOptions.PrettyPrinted)
let outputStr = String(data: outputData, encoding: NSUTF8StringEncoding)!
Customization
If you want to differ from the default generated code you can provide your own
decodeJson
or encodeJson
functions. If these already exist, no new
function will be generated.
You also need to provide your own functions for kinds that are not supported, like enums and classes.
How it works
This program calls the Swift compiler and dumps the parsed AST.
(Using the command xcrun swiftc -dump-ast SomeFile.swift
)
This AST is traversed to look for struct definitions, for each struct
decodeJson
and encodeJson
functions is generated:
extention SomeStruct {
static func decodeJson(json: AnyObject) throws -> SomeStruct {
...
}
func encodeJson() -> AnyObject {
...
}
}
Compiling
This package is written in TypeScript. To make changes to the code of JsonGen, first install TypeScript:
> npm install -g typescript
Edit the .ts
files and compile the code as follows:
> tsc lib/*.ts
Releases
- 0.4.0 - 2016-02-21 - Generate code based on JsonDecodable class.
- 0.3.0 - 2015-11-19 - Decoders with
throws
, instead of returning an optional - 0.2.2 - 2015-09-22 - Bugfix, show correct error on missing field
- 0.2.1 - 2015-09-14 - Bugfix, now works with released Xcode
- 0.2.0 - 2015-09-11 - Update to Swift 2
- 0.1.3 - 2015-07-22 - Show all Swift compiler errors
- 0.1.2 - 2015-06-01 - Support for computed properties
- 0.1.1 - 2015-05-28 - Don't generate empty files
- 0.1.0 - 2015-05-25 - Initial public release
- 0.0.0 - 2014-10-11 - Initial private version for project at Q42
Licence & Credits
JsonGen is written by Tom Lokhorst of Q42 and available under the MIT license, so feel free to use it in commercial and non-commercial projects.