如何使用 Codable 解析不同对象列表的 Json 数组？

编程问答 2022-04-24

问题描述

我有一个带有不同属性的项目列表的 json 数组。

{
    "items": [ 
        {
            "id": "1","name": "name","propertyOfA": "1243","productype": "a"

        },{
            "id": "2","propertyOfA": "12","productype": "a"
        },{
            "id": "3",{
            "id": "1","propertyOfB": "1243","productype": "b"
        },"propertyOfC": "1243","propertyOfC2": "1243","productype": "c"
        }
        ]
}

我通常做的是将其解析为：


struct RequestData: Codable {
    let items: [Item]
}

enum ProductType: String,Codable {
    case a = "A"
    case b = "B"
    case c = "C"
}

struct Item: Codable {
    let id,name: String
    let propertyOfA: String?
    let productype: String
    let propertyOfB: String?
    let propertyOfC: String?
    let propertyOfC2: String?
}

但是如果这个数组继续增长，它最终会得到一个带有大量可选属性的项目， 所以我希望每个对象都有自己的专用类

在可编码解析中添加某种桥梁，

我想要存档的内容类似于：

struct RequestData: Codable {
    let items: Items
}

struct items: Codable {
    let arrayA: [A]
    let arrayB = [B]
    let arrayC = [C]
}

struct A: Codable {
    let id: String,let name: String,let propertyOfA: String,let producttype: Productype
}

struct B {
...
}

struct C {
...
}

我可以用 Codable 做到这一点吗？

解决方法

一个合理的解决方案是具有关联值的枚举，因为类型可以由 productype 键确定。 init 方法首先使用 productype 解码 CodingKey，然后在 switch 中解码（来自 singleValueContainer）并将正确的类型/值关联到对应的情况。

enum ProductType: String,Codable {
    case a,b,c
}

struct Root : Codable {
    let items : [Product]
}

struct ProductA : Codable {
    let id,name: String
    let productype: ProductType
    let propertyOfA : String
}

struct ProductB : Codable {
    let id,name: String
    let productype: ProductType
    let propertyOfB : String
}

struct ProductC : Codable {
    let id,name: String
    let productype: ProductType
    let propertyOfC,propertyOfC2 : String
}

enum Product : Codable {
    
    case a(ProductA),b(ProductB),c(ProductC)
    
    enum CodingKeys : String,CodingKey { case productype }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let type = try  container.decode(ProductType.self,forKey: .productype)
        let singleContainer = try decoder.singleValueContainer()
        switch type {
            case .a : self = .a(try singleContainer.decode(ProductA.self))
            case .b : self = .b(try singleContainer.decode(ProductB.self))
            case .c : self = .c(try singleContainer.decode(ProductC.self))
        }
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        switch self {
            case .a(let productA): try container.encode(productA)
            case .b(let productB): try container.encode(productB)
            case .c(let productC): try container.encode(productC)
        }
    }
}

并解码

let jsonString = """
{
    "items": [
        {
            "id": "1","name": "name","propertyOfA": "1243","productype": "a"

        },{
            "id": "2","propertyOfA": "12","productype": "a"
        },{
            "id": "3",{
            "id": "1","propertyOfB": "1243","productype": "b"
        },"propertyOfC": "1243","propertyOfC2": "1243","productype": "c"
        }
        ]
}
"""
do {
    let result = try JSONDecoder().decode(Root.self,from: Data(jsonString.utf8))
    print(result)
} catch { print(error)}

要读取枚举值，还使用 ​​switch。

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