编码嵌套结构并使用单键转换为 json

Question

我有一个带有嵌套结构的对象，我想对它们进行编码，所以我有一个 json，其中这些结构的属性在 json 中的相同键下。

例如，

struct Payload: Codable {
    let meta: Meta
    
    enum CodingKeys: String, CodingKey {
        case meta = "mm"
    }
}

struct Meta: Codable {
    let application: Application?
    let platform: Platform?
    let device: Device?
}

struct Application: Codable {
    let name: String
    let version: String
}

struct Platform: Codable {
    let type: String
}

struct Device: Codable {
    let system: String
}

所以我希望 JSON 看起来像这样：

{
    "mm": {
        "name": "A"
        "version": "B"
        "type": "C"
        "system": "D"
    }
}

我只是能够以某种方式对其进行编码，所以当我添加例如 元键下的平台属性，它将删除应用程序对象之前添加的属性。

public func encode(to encoder: Encoder) throws {
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encodeIfPresent(meta.application, forKey: .meta)
    // will remove previously added properties from application
    try container.encodeIfPresent(meta.platform, forKey: .meta)
}

Answer 1

如果看起来不酷，但如果你想加入来自不同级别的多个键/值对，你必须手动创建字典

struct Payload: Encodable {
    let meta: Meta
    
    enum CodingKeys: String, CodingKey {
        case meta = "mm"
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        let dictionary = [
            "name": meta.application?.name ?? "Unknown name",
            "version":  meta.application?.version ?? "Unknown version",
            "type":  meta.platform?.type ?? "Unknown type",
            "system": meta.device?.system ?? "Unknown system"
        ]
        try container.encode(dictionary, forKey: .meta)
    }
}