如何使用Swift Decodable协议解码嵌套的JSON结构？

时间：2017-06-14 15:47:34

标签： json swift swift4 codable

这是我的JSON 

{
    "id": 1,
    "user": {
        "user_name": "Tester",
        "real_info": {
            "full_name":"Jon Doe"
        }
    },
    "reviews_count": [
        {
            "count": 4
        }
    ]
}

这是我想要保存的结构（不完整）

struct ServerResponse: Decodable {
    var id: String
    var username: String
    var fullName: String
    var reviewCount: Int

    enum CodingKeys: String, CodingKey {
       case id, 
       // How do i get nested values?
    }
}

我在解码嵌套结构时已经看过Apple's Documentation，但我仍然不明白如何正确地执行不同级别的JSON。任何帮助将不胜感激。

7 个答案:

答案 0 :(得分：74)

另一种方法是创建一个与JSON紧密匹配的中间模型（在quicktype.io之类的工具的帮助下），让Swift生成解码它的方法，然后选择你想要的部分你的最终数据模型：

// snake_case to match the JSON and hence no need to write CodingKey enums / struct
fileprivate struct RawServerResponse: Decodable {
    struct User: Decodable {
        var user_name: String
        var real_info: UserRealInfo
    }

    struct UserRealInfo: Decodable {
        var full_name: String
    }

    struct Review: Decodable {
        var count: Int
    }

    var id: Int
    var user: User
    var reviews_count: [Review]
}

struct ServerResponse: Decodable {
    var id: String
    var username: String
    var fullName: String
    var reviewCount: Int

    init(from decoder: Decoder) throws {
        let rawResponse = try RawServerResponse(from: decoder)

        // Now you can pick items that are important to your data model,
        // conveniently decoded into a Swift structure
        id = String(rawResponse.id)
        username = rawResponse.user.user_name
        fullName = rawResponse.user.real_info.full_name
        reviewCount = rawResponse.reviews_count.first!.count
    }
}

如果将来包含的值超过1，您还可以轻松遍历reviews_count。

答案 1 :(得分：64)

为了解决您的问题，您可以将RawServerResponse实现拆分为多个逻辑部分（使用Swift 5）。

＃1。实现属性和所需的编码密钥

import Foundation

struct RawServerResponse {

    enum RootKeys: String, CodingKey {
        case id, user, reviewCount = "reviews_count"
    }

    enum UserKeys: String, CodingKey {
        case userName = "user_name", realInfo = "real_info"
    }

    enum RealInfoKeys: String, CodingKey {
        case fullName = "full_name"
    }

    enum ReviewCountKeys: String, CodingKey {
        case count
    }

    let id: Int
    let userName: String
    let fullName: String
    let reviewCount: Int

}

＃2。设置id属性

的解码策略 
extension RawServerResponse: Decodable {

    init(from decoder: Decoder) throws {
        // id
        let container = try decoder.container(keyedBy: RootKeys.self)
        id = try container.decode(Int.self, forKey: .id)

        /* ... */                 
    }

}

＃3。设置userName属性

的解码策略 
extension RawServerResponse: Decodable {

    init(from decoder: Decoder) throws {
        /* ... */

        // userName
        let userContainer = try container.nestedContainer(keyedBy: UserKeys.self, forKey: .user)
        userName = try userContainer.decode(String.self, forKey: .userName)

        /* ... */
    }

}

＃4。设置fullName属性

的解码策略 
extension RawServerResponse: Decodable {

    init(from decoder: Decoder) throws {
        /* ... */

        // fullName
        let realInfoKeysContainer = try userContainer.nestedContainer(keyedBy: RealInfoKeys.self, forKey: .realInfo)
        fullName = try realInfoKeysContainer.decode(String.self, forKey: .fullName)

        /* ... */
    }

}

＃5。设置reviewCount属性

的解码策略 
extension RawServerResponse: Decodable {

    init(from decoder: Decoder) throws {
        /* ...*/        

        // reviewCount
        var reviewUnkeyedContainer = try container.nestedUnkeyedContainer(forKey: .reviewCount)
        var reviewCountArray = [Int]()
        while !reviewUnkeyedContainer.isAtEnd {
            let reviewCountContainer = try reviewUnkeyedContainer.nestedContainer(keyedBy: ReviewCountKeys.self)
            reviewCountArray.append(try reviewCountContainer.decode(Int.self, forKey: .count))
        }
        guard let reviewCount = reviewCountArray.first else {
            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: container.codingPath + [RootKeys.reviewCount], debugDescription: "reviews_count cannot be empty"))
        }
        self.reviewCount = reviewCount
    }

}

完成实施

import Foundation

struct RawServerResponse {

    enum RootKeys: String, CodingKey {
        case id, user, reviewCount = "reviews_count"
    }

    enum UserKeys: String, CodingKey {
        case userName = "user_name", realInfo = "real_info"
    }

    enum RealInfoKeys: String, CodingKey {
        case fullName = "full_name"
    }

    enum ReviewCountKeys: String, CodingKey {
        case count
    }

    let id: Int
    let userName: String
    let fullName: String
    let reviewCount: Int

}

extension RawServerResponse: Decodable {

    init(from decoder: Decoder) throws {
        // id
        let container = try decoder.container(keyedBy: RootKeys.self)
        id = try container.decode(Int.self, forKey: .id)

        // userName
        let userContainer = try container.nestedContainer(keyedBy: UserKeys.self, forKey: .user)
        userName = try userContainer.decode(String.self, forKey: .userName)

        // fullName
        let realInfoKeysContainer = try userContainer.nestedContainer(keyedBy: RealInfoKeys.self, forKey: .realInfo)
        fullName = try realInfoKeysContainer.decode(String.self, forKey: .fullName)

        // reviewCount
        var reviewUnkeyedContainer = try container.nestedUnkeyedContainer(forKey: .reviewCount)
        var reviewCountArray = [Int]()
        while !reviewUnkeyedContainer.isAtEnd {
            let reviewCountContainer = try reviewUnkeyedContainer.nestedContainer(keyedBy: ReviewCountKeys.self)
            reviewCountArray.append(try reviewCountContainer.decode(Int.self, forKey: .count))
        }
        guard let reviewCount = reviewCountArray.first else {
            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: container.codingPath + [RootKeys.reviewCount], debugDescription: "reviews_count cannot be empty"))
        }
        self.reviewCount = reviewCount
    }

}

用法

let jsonString = """
{
    "id": 1,
    "user": {
        "user_name": "Tester",
        "real_info": {
            "full_name":"Jon Doe"
        }
    },
    "reviews_count": [
    {
    "count": 4
    }
    ]
}
"""

let jsonData = jsonString.data(using: .utf8)!
let decoder = JSONDecoder()
let serverResponse = try! decoder.decode(RawServerResponse.self, from: jsonData)
dump(serverResponse)

/*
prints:
▿ RawServerResponse #1 in __lldb_expr_389
  - id: 1
  - user: "Tester"
  - fullName: "Jon Doe"
  - reviewCount: 4
*/

答案 2 :(得分：22)

我不建议使用所有一个大的CodingKeys枚举来解码JSON所需的密钥，而是建议将密钥拆分为每个 ，使用嵌套枚举来保留层次结构：

// top-level JSON object keys
private enum CodingKeys : String, CodingKey {

    // using camelCase case names, with snake_case raw values where necessary.
    // the raw values are what's used as the actual keys for the JSON object,
    // and default to the case name unless otherwise specified.
    case id, user, reviewsCount = "reviews_count"

    // "user" JSON object keys
    enum User : String, CodingKey {
        case username = "user_name", realInfo = "real_info"

        // "real_info" JSON object keys
        enum RealInfo : String, CodingKey {
            case fullName = "full_name"
        }
    }

    // nested JSON objects in "reviews" keys
    enum ReviewsCount : String, CodingKey {
        case count
    }
}

这样可以更轻松地跟踪JSON中每个级别的键。

现在，请记住：

  • keyed container用于解码JSON对象，并使用CodingKey符合类型（例如我们上面定义的那些）进行解码。

  • unkeyed container用于解码JSON数组，并按顺序解码（即每次在其上调用解码或嵌套容器方法时，它都会前进到数组中的下一个元素）。请参阅答案的第二部分，了解如何迭代一个。

使用container(keyedBy:)从解码器获取顶级键控容器后（因为您在顶层有一个JSON对象），您可以重复使用这些方法：

例如：

struct ServerResponse : Decodable {

    var id: Int, username: String, fullName: String, reviewCount: Int

    private enum CodingKeys : String, CodingKey { /* see above definition in answer */ }

    init(from decoder: Decoder) throws {

        // top-level container
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.id = try container.decode(Int.self, forKey: .id)

        // container for { "user_name": "Tester", "real_info": { "full_name": "Jon Doe" } }
        let userContainer =
            try container.nestedContainer(keyedBy: CodingKeys.User.self, forKey: .user)

        self.username = try userContainer.decode(String.self, forKey: .username)

        // container for { "full_name": "Jon Doe" }
        let realInfoContainer =
            try userContainer.nestedContainer(keyedBy: CodingKeys.User.RealInfo.self,
                                              forKey: .realInfo)

        self.fullName = try realInfoContainer.decode(String.self, forKey: .fullName)

        // container for [{ "count": 4 }] – must be a var, as calling a nested container
        // method on it advances it to the next element.
        var reviewCountContainer =
            try container.nestedUnkeyedContainer(forKey: .reviewsCount)

        // container for { "count" : 4 }
        // (note that we're only considering the first element of the array)
        let firstReviewCountContainer =
            try reviewCountContainer.nestedContainer(keyedBy: CodingKeys.ReviewsCount.self)

        self.reviewCount = try firstReviewCountContainer.decode(Int.self, forKey: .count)
    }
}

解码示例：

let jsonData = """
{
  "id": 1,
  "user": {
    "user_name": "Tester",
    "real_info": {
    "full_name":"Jon Doe"
  }
  },
  "reviews_count": [
    {
      "count": 4
    }
  ]
}
""".data(using: .utf8)!

do {
    let response = try JSONDecoder().decode(ServerResponse.self, from: jsonData)
    print(response)
} catch {
    print(error)
}

// ServerResponse(id: 1, username: "Tester", fullName: "Jon Doe", reviewCount: 4)

通过未加密钥的容器进行迭代

考虑您希望reviewCount成为[Int]的情况，其中每个元素代表嵌套JSON中"count"键的值：

  "reviews_count": [
    {
      "count": 4
    },
    {
      "count": 5
    }
  ]

您需要遍历嵌套的无键容器，在每次迭代时获取嵌套的键控容器，并解码"count"键的值。您可以使用未加密的容器的count属性来预先分配结果数组，然后使用isAtEnd属性来迭代它。

例如：

struct ServerResponse : Decodable {

    var id: Int
    var username: String
    var fullName: String
    var reviewCounts = [Int]()

    // ...

    init(from decoder: Decoder) throws {

        // ...

        // container for [{ "count": 4 }, { "count": 5 }]
        var reviewCountContainer =
            try container.nestedUnkeyedContainer(forKey: .reviewsCount)

        // pre-allocate the reviewCounts array if we can
        if let count = reviewCountContainer.count {
            self.reviewCounts.reserveCapacity(count)
        }

        // iterate through each of the nested keyed containers, getting the
        // value for the "count" key, and appending to the array.
        while !reviewCountContainer.isAtEnd {

            // container for a single nested object in the array, e.g { "count": 4 }
            let nestedReviewCountContainer = try reviewCountContainer.nestedContainer(
                                                 keyedBy: CodingKeys.ReviewsCount.self)

            self.reviewCounts.append(
                try nestedReviewCountContainer.decode(Int.self, forKey: .count)
            )
        }
    }
}

答案 3 :(得分：14)

这些家伙已经回答了我的问题，但我只是想在这里发布这个链接，这使得这更容易 - ＆gt; https://app.quicktype.io/#l=swift

只需在左侧窗格中发布您的JSON响应，然后在右侧观看您的模型生成。当你刚刚开始时，这可以提供帮助。

答案 4 :(得分：3)

  1. 将json文件复制到https://app.quicktype.io
  2. 选择Swift（如果使用Swift 5，请检查Swift 5的兼容性开关）
  3. 使用以下代码对文件进行解码
  4. Voila！
let file = "data.json"

guard let url = Bundle.main.url(forResource: "data", withExtension: "json") else{
    fatalError("Failed to locate \(file) in bundle.")
}

guard let data = try? Data(contentsOf: url) else{
    fatalError("Failed to locate \(file) in bundle.")
}

let yourObject = try? JSONDecoder().decode(YourModel.self, from: data)

答案 5 :(得分：0)

已经发布了许多好的答案，但是IMO还没有描述一种更简单的方法。

使用snake_case_notation编写JSON字段名称时，您仍然可以在Swift文件中使用camelCaseNotation。

您只需要设置

decoder.keyDecodingStrategy = .convertFromSnakeCase

此☝️行之后，Swift将自动将JSON中的所有snake_case字段与Swift模型中的camelCase字段进行匹配。

例如

user_name` -> userName
reviews_count -> `reviewsCount
...

这是完整的代码

1。编写模型

struct Response: Codable {

    let id: Int
    let user: User
    let reviewsCount: [ReviewCount]

    struct User: Codable {
        let userName: String

        struct RealInfo: Codable {
            let fullName: String
        }
    }

    struct ReviewCount: Codable {
        let count: Int
    }
}

2。设置解码器

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase

3。解码

do {
    let response = try? decoder.decode(Response.self, from: data)
    print(response)
} catch {
    debugPrint(error)
}

答案 6 :(得分：-1)

您也可以使用我准备的库KeyedCodable。它将需要更少的代码。让我知道你对它的看法。

struct ServerResponse: Decodable, Keyedable {
  var id: String!
  var username: String!
  var fullName: String!
  var reviewCount: Int!

  private struct ReviewsCount: Codable {
    var count: Int
  }

  mutating func map(map: KeyMap) throws {
    var id: Int!
    try id <<- map["id"]
    self.id = String(id)

    try username <<- map["user.user_name"]
    try fullName <<- map["user.real_info.full_name"]

    var reviewCount: [ReviewsCount]!
    try reviewCount <<- map["reviews_count"]
    self.reviewCount = reviewCount[0].count
  }

  init(from decoder: Decoder) throws {
    try KeyedDecoder(with: decoder).decode(to: &self)
  }
}
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