Codable，只能从字典中解码值

Question

我有一个API的json响应。这将返回一个也是一个Dictionary的值。如何才能实现仅存储/映射此字典的值。这里是一个可以简单地放入一个游乐场的例子：

id = ["$oid": "591ae6cb9d1fa2b6e47edc33"] 

只应

id = "591ae6cb9d1fa2b6e47edc33" 

这里是一个可以简单地放入一个游乐场的例子：

import Foundation 

struct Location : Decodable { 
    enum CodingKeys : String, CodingKey { 
     case id = "_id" 
    } 
    var id : [String:String]? // this should be only a string with the value of "$oid" 
} 

extension Location { 
    public init(from decoder: Decoder) throws { 
     let values = try decoder.container(keyedBy: CodingKeys.self) 
     id = try values.decode([String:String]?.self, forKey: .id) 
    } 
} 


var json = """ 
[ 
    { 
     "_id": { 
      "$oid": "591ae6cb9d1fa2b6e47edc33" 
     } 
    }, 
    { 
     "_id": { 
      "$oid": "591ae6cd9d1fa2b6e47edc34" 
     } 
    } 
] 

""".replacingOccurrences(of: "}\n{", with: "}\\n{").data(using: .utf8)! 

let decoder = JSONDecoder() 

do { 
    let locations = try decoder.decode([Location].self, from: json) 
    locations.forEach { print($0) } 
} catch { 
    print(error.localizedDescription) 
} 

Answer 1

你几乎在那里：

struct Location { 
    var id: String 
} 

extension Location: Decodable { 
    private enum CodingKeys: String, CodingKey { 
     case id = "_id" 
    } 

    public init(from decoder: Decoder) throws { 
     let values = try decoder.container(keyedBy: CodingKeys.self) 
     let _id = try values.decode([String: String].self, forKey: .id) 
     id = _id["$oid"]! 
    } 
} 

如果您在JSON数据中有_id下的mote键，我强烈建议您创建一个私有结构体来代表类型安全性的结构。