json - ObjectMapper 如何基于 JSON 映射不同的对象

Question

我正在使用 ObjectMapper ( https://github.com/Hearst-DD/ObjectMapper ) 将我的 JSON 映射到 Swift 对象。

假设我有这个 JSON 结构:

{
  animals: [
    {
      "type": "Cat",
      "weight": 23,
      "catchMice": true
    },
    {
      "type": "Fish",
      "weight": 1,
      "swim": true
    }
  ]
}

我有以下 Swift 对象:

class Foo: Mappable {
  var animals: [Animal] = []

  func mapping(map: Map) {
    animals <- map["animals"] //But I want to be able to distinguish between Cat and Fish objects here
  }
}

class Animal: Mappable {
  var type: String?
  var weight: Double?

  required init?(map: Map) {}

  func mapping(map: Map) {
    type <- map["type"]
    weight <- map["weight"]
  }
}

class Cat: Animal { // How do I make use of this class
  var catchMice: Bool?
}

class Fish: Animal { // How do I make use of this class 
  var swim: Bool?
}

如何使用 JSON 对象中的 type 键区分映射中的 Cat 和 Fish？非常感谢!

Answer 1

详情

• Xcode 10.2.1 (10E1001)、Swift 5

json文件

{
    "animals": [
        {
            "id": 1,
            "name": "Cat",
            "type": "cat",
            "weight": 23,
            "area": ["home", "street"],
            "can_climb_trees": true,
            "competence": [
                { "id": 1, "name": "to catch mouse" },
                { "id": 2, "name": "to mew" },
                { "id": 3, "name": "to wake people up in the morning" },
                { "id": 4, "name": "to eat fish" }
            ]
        },
        {
            "id": 2,
            "name": "fish",
            "type": "fish",
            "weight": 1,
            "area": ["ocean", "lake"],
            "can_swim": false,
            "competence": [
                { "id": 5, "name": "to swim" },
                { "id": 6, "name": "to tease a cat" }
            ]
        },
        {
            "id": 3,
            "name": "dog",
            "weight": 55,
            "area": ["house", "street"],
            "competence": [
                { "id": 5, "name": "to bring newspaper" },
                { "id": 6, "name": "to a good booy" }
            ]
        },
        {
            "id": 4,
            "name": "Cat",
            "type": "cat",
            "weight": 23,
            "area": ["home", "street"],
            "can_climb_trees": true,
            "competence": [
                { "id": 1, "name": "to catch mouse" },
                { "id": 2, "name": "to mew" },
                { "id": 3, "name": "to wake people up in the morning" },
                { "id": 4, "name": "to eat fish" }
            ]
        }
    ]
}

---

ObjectMapper 示例

Detect objects in array

import Foundation
import ObjectMapper

class AnimalsArrayTransformType: TransformType {

    public typealias Object = [Animal]
    public typealias JSON = [[String: Any]]

    func transformToJSON(_ value: [Animal]?) -> [[String : Any]]? {
        guard let animals = value else { return nil }
        return animals.map { $0.toJSON() }
    }

    func transformFromJSON(_ value: Any?) -> [Animal]? {
        guard let animals = value as? [[String: Any]] else { return nil }
        return animals.compactMap { dictionary -> Animal? in
            if let cat = Cat(JSON: dictionary) { return cat }
            if let fish = Fish(JSON: dictionary) { return fish }
            if let animal = Animal(JSON: dictionary) { return animal }
            return nil
        }
    }
}

Mapping classes

import Foundation
import ObjectMapper

class Animals: Mappable, CustomStringConvertible {
    private(set) var animals: [Animal] = []
    required init?(map: Map) { }

    func mapping(map: Map) {
        animals <- (map["animals"], AnimalsArrayTransformType())
    }
}

class BaseObject: Mappable, CustomStringConvertible {
    private(set) var id: Int?
    private(set) var name: String?

    required init?(map: Map) { mapping(map: map) }

    func mapping(map: Map) {
        id <- map["id"]
        name <- map["name"]
    }
}

class Animal: BaseObject {
    private(set) var type: String?
    private(set) var weight: Double?
    private(set) var area: [String]?
    private(set) var competence: [BaseObject]?

    required init?(map: Map) { super.init(map: map) }

    override func mapping(map: Map) {
        super.mapping(map: map)
        type <- map["type"]
        weight <- map["weight"]
        area <- map["area"]
        competence <- map["competence"]
    }
}

class Cat: Animal {
    private(set) var canClimbTrees: Bool?

    required init?(map: Map) {
        super.init(map: map)
        if canClimbTrees == nil { return nil }
    }

    override func mapping(map: Map) {
        super.mapping(map: map)
        canClimbTrees <- map["can_climb_trees"]
    }
}

class Fish: Animal {
    private(set) var canSwim: Bool?

    required init?(map: Map) {
        super.init(map: map)
        if canSwim == nil { return nil }
    }

    override func mapping(map: Map) {
        super.mapping(map: map)
        canSwim <- map["can_swim"]
    }
}

Helpers

extension Mappable {
    var description: String {
        return toJSONString(prettyPrint: true) ?? "\(self)"
    }
}

Usage (read json from file)

    func sample() {
        if let path = Bundle.main.path(forResource: "data", ofType: "json") {
            do {
                let text = try String(contentsOfFile: path, encoding: .utf8)
                if let dict = try JSONSerialization.jsonObject(with: text.data(using: .utf8)!, options: JSONSerialization.ReadingOptions.allowFragments) as? [String: Any] {
                    if let data = Animals(JSON: dict) {
                        print(data.animals.map {"class: \(type(of: $0))" }.joined(separator: ", ") )
                        // class: Cat, class: Fish, class: Animal
                        print("===============\n\(data)")
                    }
                }
            }catch {
                print("\(error.localizedDescription)")
            }
        }
    }

---

可编码示例

Detect objects in array

class Animals: Codable {

    fileprivate enum CodingKeys: String, CodingKey {
        case animals
    }

    private(set) var animals: [Animal]

    required init(from decoder: Decoder) throws {
        self.animals = []
        let container = try decoder.container(keyedBy: CodingKeys.self)
        var unkeyedDecodingContainer = try container.nestedUnkeyedContainer(forKey: .animals)
        while !unkeyedDecodingContainer.isAtEnd {
            if let obj = try? unkeyedDecodingContainer.decode(Cat.self) {
                animals.append(obj)
                continue
            }

            if let obj = try? unkeyedDecodingContainer.decode(Fish.self) {
                animals.append(obj)
                continue
            }

            if let obj = try? unkeyedDecodingContainer.decode(Animal.self) {
                animals.append(obj)
                continue
            }
        }
    }
}

Mapping classes

enum AnimalType: String, Codable {
    case cat = "cat", fish = "fish"
}

class BaseObject: Codable {
    private(set) var id: Int?
    private(set) var name: String?
}

class Animal: BaseObject {
    private(set) var type: AnimalType?
    private(set) var weight: Int?
    private(set) var area: [String]?
    private(set) var competence: [BaseObject]?

    private enum CodingKeys: String, CodingKey {
        case type, weight, area, competence
    }

    override func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encodeIfPresent(type, forKey: .type)
        try container.encodeIfPresent(weight, forKey: .weight)
        try container.encodeIfPresent(area, forKey: .area)
        try container.encodeIfPresent(competence, forKey: .competence)
        try super.encode(to: encoder)
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        type = try container.decodeIfPresent(AnimalType.self, forKey: .type)
        weight = try container.decodeIfPresent(Int.self, forKey: .weight)
        area = try container.decodeIfPresent([String].self, forKey:  .area)
        competence = try container.decodeIfPresent([BaseObject].self, forKey: .competence)
        try super.init(from: decoder)
    }
}

class Cat: Animal {
    private(set) var canClimbTrees: Bool

    private enum CodingKeys: String, CodingKey {
        case canClimbTrees = "can_climb_trees"
    }

    override func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encodeIfPresent(canClimbTrees, forKey: .canClimbTrees)
        try super.encode(to: encoder)
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.canClimbTrees = try container.decode(Bool.self, forKey: .canClimbTrees)
        try super.init(from: decoder)
    }
}


class Fish: Animal {

    private(set) var canSwim: Bool

    enum CodingKeys: String, CaseIterable, CodingKey {
        case canSwim = "can_swim"
    }

    override func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encodeIfPresent(canSwim, forKey: .canSwim)
        try super.encode(to: encoder)
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.canSwim = try container.decode(Bool.self, forKey: .canSwim)
        try super.init(from: decoder)
    }
}

Helpers

extension Decodable where Self : Encodable {

    dynamic func format(options: JSONEncoder.OutputFormatting) -> String {
        let encoder = JSONEncoder()
        encoder.outputFormatting = options
        do {
            let jsonData = try encoder.encode(self)
            if let jsonString = String(data: jsonData, encoding: .utf8) { return "\(jsonString)" }
        } catch {
            print("\(error.localizedDescription)")
        }
        return "nil"
    }
}

Usage (read json from file)

func sample() {
    if let path = Bundle.main.path(forResource: "data", ofType: "json") {
        do {
            guard let data = try String(contentsOfFile: path, encoding: .utf8).data(using: .utf8) else { return }
            let decoder = JSONDecoder()
            let result = try decoder.decode(Animals.self, from: data)
            print(result.animals.map {"\(type(of: $0))" } )
            //print("===============")
            //print(result.format(options: .prettyPrinted))
        } catch let error {
            print("\(error.localizedDescription)")
        }
    }
}

---

输出

["猫", "鱼", "动物", "猫"]