处理包含多种类型的 JSON 数组 - Swift 4 Decodable

Posted 2023-02-18

【中文标题】处理包含多种类型的 JSON 数组 - Swift 4 Decodable

【英文标题】：Handling JSON Array Containing Multiple Types - Swift 4 Decodable

【发布时间】：2018-09-07 09:00:04

【问题描述】：

我正在尝试使用 Swift 4 Decodable 来解析包含两种不同类型对象的数组。数据看起来像这样，included 数组是同时包含 Member 和 ImageMedium 对象的数组：

  "data": [
    "id": "8f7cbbac-c133-4b5e-a2ec-1f32353018fa",
    "type": "post",
    "title": "Test Post 1",
    "owner-id": "8986563c-438c-4d77-8115-9e5de2b6e477",
    "owner-type": "member"
  , 
    "id": "f6b3c640-a58b-449f-93c7-f6cb7b569a9c",
    "type": "post",
    "title": "Test Post 2",
    "owner-id": "38d845a4-db66-48b9-9c15-d857166e255e",
    "owner-type": "member"
  ],
  "included": [
    "id": "8986563c-438c-4d77-8115-9e5de2b6e477",
    "type": "member",
    "first-name": "John",
    "last-name": "Smith"
  , 
    "id": "d7218ca1-de53-4832-bb8f-dbceb6747e98",
    "type": "image-medium",
    "asset-url": "https://faketest.com/fake-test-1.png",
    "owner-id": "f6b3c640-a58b-449f-93c7-f6cb7b569a9c",
    "owner-type": "post"
  , 
    "id": "c59b8c72-13fc-44fd-8ef9-4b0f8fa486a0",
    "type": "image-medium",
    "asset-url": "https://faketest.com/fake-test-2.png",
    "owner-id": "8f7cbbac-c133-4b5e-a2ec-1f32353018fa",
    "owner-type": "post"
  , 
    "id": "38d845a4-db66-48b9-9c15-d857166e255e",
    "type": "member",
    "first-name": "Jack",
    "last-name": "Doe"
  ]

我已经尝试了很多不同的方法来使用 Decodable 干净地解决这个问题，但到目前为止，唯一对我有用的是为 Included 创建一个结构，其中包含两个对象的所有属性作为可选，就像这样：

struct Root: Decodable 
    let data: [Post]?
    let included: [Included]?


struct Post: Decodable 
    let id: String?
    let type: String?
    let title: String?
    let ownerId: String?
    let ownerType: String?

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case title
        case ownerId = "owner-id"
        case ownerType = "owner-type"
    


struct Included: Decodable 
    let id: String?
    let type: String?
    let assetUrl: String?
    let ownerId: String?
    let ownerType: String?
    let firstName: String?
    let lastName: String?

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case assetUrl = "asset-url"
        case ownerId = "owner-id"
        case ownerType = "owner-type"
        case firstName = "first-name"
        case lastName = "last-name"
    
 

这可以通过实现一种方法来实现，该方法根据其type 属性从Included 结构创建Member 和ImageMedium 对象，但它显然不太理想。我希望有一种方法可以使用自定义init(from decoder: Decoder) 来实现这一点，但我还没有让它工作。有什么想法吗？

【问题讨论】：

当然，您应该使用带有这些类型关联值的 Codable 枚举来处理它。

@user28434 你能详细说明一下吗？如果有帮助，我编辑了问题以包含 Root 和 Post 结构。

链接：***.com/questions/48314724/…

【参考方案1】：

我的建议是对所有项目使用单一类型Post。为了区分不同的类型，将type键解码为枚举，并根据情况对属性进行解码。

这需要将所有非全局属性声明为var。

struct Root : Decodable 
    let data : [Post]
    let included : [Post]


enum PostType : String, Decodable 
    case member, post, imageMedium = "image-medium"


struct Post : Decodable 
    let id: String
    let type: PostType

    var title: String?
    var assetUrl: String?
    var ownerId: String?
    var ownerType: String?
    var firstName: String?
    var lastName: String?

    enum CodingKeys: String, CodingKey 
        case id, type, title
        case assetUrl = "asset-url"
        case ownerId = "owner-id"
        case ownerType = "owner-type"
        case firstName = "first-name"
        case lastName = "last-name"
    

    init(from decoder: Decoder) throws 
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(String.self, forKey: .id)
        type = try container.decode(PostType.self, forKey: .type)
        switch type 
        case .member:
            firstName = try container.decode(String.self, forKey: .firstName)
            lastName = try container.decode(String.self, forKey: .lastName)
        case .post:
            title = try container.decode(String.self, forKey: .title)
            ownerId = try container.decode(String.self, forKey: .ownerId)
            ownerType = try container.decode(String.self, forKey: .ownerType)
        case .imageMedium:
            assetUrl = try container.decode(String.self, forKey: .assetUrl)
            ownerId = try container.decode(String.self, forKey: .ownerId)
            ownerType = try container.decode(String.self, forKey: .ownerType)
        
    
 

【讨论】：

That requires to declare all non-global properties as var. — 真的没有。它需要声明Optional，但它可以是let，但你应该在init内部使用nil手动初始化它们。

【参考方案2】：

这是基于初始编辑，有一些冗余代码，但总体思路应该可以理解：

enum Post: Codable 
    case post(id: UUID, title: String, ownerId: UUID, ownerType: PostOwner)
    case member(id: UUID, firstName: String, lastName: String)
    case imageMedium(id: UUID, assetURL: URL, ownerId: UUID, ownerType: ImageOwner)

    enum PostType: String, Codable 
        case post
        case member
        case imageMedium = "image-medium"
    

    enum PostOwner: String, Codable 
        case member
    

    enum ImageOwner: String, Codable 
        case post
    

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case title
        case assetUrl = "asset-url"
        case ownerId = "owner-id"
        case ownerType = "owner-type"
        case firstName = "first-name"
        case lastName = "last-name"
    

    init(from decoder: Decoder) throws 
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let id = try container.decode(UUID.self, forKey: .id)
        let type = try container.decode(PostType.self, forKey: .type)

        switch type 
        case .post:
            let title = try container.decode(String.self, forKey: .title)
            let ownerId = try container.decode(UUID.self, forKey: .ownerId)
            let ownerType = try container.decode(PostOwner.self, forKey: .ownerType)
            self = .post(id: id, title: title, ownerId: ownerId, ownerType: ownerType)
        case .member:
            let firstName = try container.decode(String.self, forKey: .firstName)
            let lastName = try container.decode(String.self, forKey: .lastName)
            self = .member(id: id, firstName: firstName, lastName: lastName)
        case .imageMedium:
            let assetURL = try container.decode(URL.self, forKey: .assetUrl)
            let ownerId = try container.decode(UUID.self, forKey: .ownerId)
            let ownerType = try container.decode(ImageOwner.self, forKey: .ownerType)
            self = .imageMedium(id: id, assetURL: assetURL, ownerId: ownerId, ownerType: ownerType)
        
    

    func encode(to encoder: Encoder) throws 
        var container = encoder.container(keyedBy: CodingKeys.self)
        switch self 
        case .post(let id, let title, let ownerId, let ownerType):
            try container.encode(PostType.post, forKey: .type)
            try container.encode(id, forKey: .id)
            try container.encode(title, forKey: .title)
            try container.encode(ownerId, forKey: .ownerId)
            try container.encode(ownerType, forKey: .ownerType)
        case .member(let id, let firstName, let lastName):
            try container.encode(PostType.member, forKey: .type)
            try container.encode(id, forKey: .id)
            try container.encode(firstName, forKey: .firstName)
            try container.encode(lastName, forKey: .lastName)
        case .imageMedium(let id, let assetURL, let ownerId, let ownerType):
            try container.encode(PostType.imageMedium, forKey: .type)
            try container.encode(id, forKey: .id)
            try container.encode(assetURL, forKey: .assetUrl)
            try container.encode(ownerId, forKey: .ownerId)
            try container.encode(ownerType, forKey: .ownerType)
        
    


let jsonDecoder = JSONDecoder()
let result = try jsonDecoder.decode([String: [Post]].self, from: yourJSONData)
print(result)

对于当前帖子类型中未使用的字段，它的选项为零，UUIDs 的类型为UUID，URLs 的类型为URL，而不是Strings。

ownerType 被键入为 PostOwner 和 ImageOwner 用于 .post 和 .imageMedium 以获得额外的类型安全性。

编辑：好的，我检查了问题的编辑：在您的 json 中，只有“.post”进入“数据”，其余进入“包含”。在我的答案中，Posts 和 Includeds 合并为一种类型。

所以应该是这样的：

struct Post: Codable 
    let id: UUID
    let title: String
    let ownerId: UUID
    let ownerType: PostOwner

    enum PostOwner: String, Codable 
        case member
    

    enum CodingKeys: String, CodingKey 
        case id
        case title
        case ownerId = "owner-id"
        case ownerType = "owner-type"
    


enum Included: Codable 
    case member(id: UUID, firstName: String, lastName: String)
    case imageMedium(id: UUID, assetURL: URL, ownerId: UUID, ownerType: ImageOwner)

    enum PostType: String, Codable 
        case member
        case imageMedium = "image-medium"
    

    enum ImageOwner: String, Codable 
        case post
    

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case title
        case assetUrl = "asset-url"
        case ownerId = "owner-id"
        case ownerType = "owner-type"
        case firstName = "first-name"
        case lastName = "last-name"
    

    init(from decoder: Decoder) throws 
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let id = try container.decode(UUID.self, forKey: .id)
        let type = try container.decode(PostType.self, forKey: .type)

        switch type 
        case .member:
            let firstName = try container.decode(String.self, forKey: .firstName)
            let lastName = try container.decode(String.self, forKey: .lastName)
            self = .member(id: id, firstName: firstName, lastName: lastName)
        case .imageMedium:
            let assetURL = try container.decode(URL.self, forKey: .assetUrl)
            let ownerId = try container.decode(UUID.self, forKey: .ownerId)
            let ownerType = try container.decode(ImageOwner.self, forKey: .ownerType)
            self = .imageMedium(id: id, assetURL: assetURL, ownerId: ownerId, ownerType: ownerType)
        
    

    func encode(to encoder: Encoder) throws 
        var container = encoder.container(keyedBy: CodingKeys.self)
        switch self 
        case .member(let id, let firstName, let lastName):
            try container.encode(PostType.member, forKey: .type)
            try container.encode(id, forKey: .id)
            try container.encode(firstName, forKey: .firstName)
            try container.encode(lastName, forKey: .lastName)
        case .imageMedium(let id, let assetURL, let ownerId, let ownerType):
            try container.encode(PostType.imageMedium, forKey: .type)
            try container.encode(id, forKey: .id)
            try container.encode(assetURL, forKey: .assetUrl)
            try container.encode(ownerId, forKey: .ownerId)
            try container.encode(ownerType, forKey: .ownerType)
        
    

Post类型解析/验证可以/应该通过手动编码init(from: )来添加。

【参考方案3】：

我想出了如何将混合的included 数组解码为两个数组，每个数组都具有一种类型。与使用一个结构来覆盖多种类型的数据相比，使用两个 Decodable 结构更容易处理，也更通用。

对于任何感兴趣的人来说，这就是我的最终解决方案：

struct Root: Decodable 
    let data: [Post]?
    let members: [Member]
    let images: [ImageMedium]

    init(from decoder: Decoder) throws 

        let container = try decoder.container(keyedBy: CodingKeys.self)

        data = try container.decode([Post].self, forKey: .data)

        var includedArray = try container.nestedUnkeyedContainer(forKey: .included)
        var membersArray: [Member] = []
        var imagesArray: [ImageMedium] = []

        while !includedArray.isAtEnd 

            do 
                if let member = try? includedArray.decode(Member.self) 
                    membersArray.append(member)
                
                else if let image = try? includedArray.decode(ImageMedium.self) 
                    imagesArray.append(image)
                
            
        
        members = membersArray
        images = imagesArray
    

    enum CodingKeys: String, CodingKey 
        case data
        case included
    


struct Post: Decodable 
    let id: String?
    let type: String?
    let title: String?
    let ownerId: String?
    let ownerType: String?

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case title
        case ownerId = "owner-id"
        case ownerType = "owner-type"
    


struct Member: Decodable 
    let id: String?
    let type: String?
    let firstName: String?
    let lastName: String?

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case firstName = "first-name"
        case lastName = "last-name"
    


struct ImageMedium: Decodable 
    let id: String?
    let type: String?
    let assetUrl: String?
    let ownerId: String?
    let ownerType: String?

    enum CodingKeys: String, CodingKey 
        case id
        case type
        case assetUrl = "asset-url"
        case ownerId = "owner-id"
        case ownerType = "owner-type"
    

【讨论】：

该解决方案有效。但它会丢弃从included 解码的元素的排序信息。