json - Swift 可编码 : encode nil as an empty object

Question

如何将 nil 属性编码为空 JSON 对象？

struct Foo: Encodable {
    let id = 10
    let bar: Bar? = nil
}

struct Bar: Encodable {
    let number: Int
}

let data = try! JSONEncoder().encode(Foo())

print(String(data: data, encoding: .utf8)!)

打印出来:

"{"id":7}"

我想要的是:

"{"id":7, "bar":{}}"

Answer 1

当 bar = nil

时，您可以向 encoder 引入一个没有属性的空结构

struct Foo: Encodable {
    let id = 10
    let bar: Bar? = nil
    
    enum CodingKeys : String, CodingKey {
        case id
        case bar
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(id, forKey: .id)
        
        if let bar = bar {
            try container.encode(bar, forKey: .bar)
        }
        else {
            try container.encode(Empty(), forKey: .bar)
        }
    }
}

struct Bar: Encodable {
    let number: Int
}

struct Empty: Encodable {
}