如何忽略编码中的零json值

Question

我现在拿到了Auto-Renewable和Non-Renewable的收据。但是Non-Renewable没有带着expires_date json密钥回来。我怎么能忽视这个。我试图避免让expires_date成为一个可选的选项。当我可选的时候，苹果会发回一个回复。有没有办法不让expires_date成为可选的，就可以解码json。

struct Receipt: Codable {

    let expiresDate: String

    private enum CodingKeys: String, CodingKey {
        case expiresDate = "expires_date"
    }
}

现在我可以

“没有与键CodingKeys相关联的值(stringValue：\"expires_date\"，intValue: nil) (\”expires_date\“)。

Answer 1

在没有合并到默认值之前，您必须实现自己的init(from: Decoder)并使用decodeIfPresent(_:forKey:)。

struct Receipt: Codable {
    let expiresDate: String
    
    enum CodingKeys: String, CodingKey {
        case expiresDate = "expires_date"
    }
    
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)        
        self.expiresDate = try values.decodeIfPresent(String.self, forKey: .expiresDate)
            ?? "1970" //Default value
    }        
}

注意：

• 如果Receipt有更多的键值对，那么您也必须手动对它们进行解码。

用法示例：

let data = """
[{
  "expires_date": "2019"
},
{

}]
""".data(using: .utf8)!

do {
    let obj = try JSONDecoder().decode([Receipt].self, from: data)
    print(obj)
}
catch {
    print(error)
}

Answer 2

手动解码如何：

struct Receipt: Codable {

    let expiresDate: String

    private enum CodingKeys: String, CodingKey {
        case expiresDate = "expires_date"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        if let expDate = try? values.decode(String.self, forKey: .expiresDate) {
            self.expiresDate = expDate
        } else {
            self.expiresDate = "sth"
        }
    }
}

示例：

struct Receipt: Codable {

    let expiresDate: String
    let b: String

    private enum CodingKeys: String, CodingKey {
        case expiresDate = "expires_date"
        case b = "b"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        if let expDate = try? values.decode(String.self, forKey: .expiresDate) {
            self.expiresDate = expDate
        } else {
            self.expiresDate = "sth"
        }
        b = try values.decode(String.self, forKey: .b)
    }
}


let a = """
{
    "b": "asdf"
}
""".data(using: .utf8)!
let myStruct = try JSONDecoder().decode(Receipt.self, from: a)
print(myStruct) //Receipt(expiresDate: "sth", b: "asdf")