如何使用Codable解析不同对象列表的Json数组

Question

我有一个json数组，它有一个不同属性的项列表。

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

我通常所做的是将其解析为类似的内容

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?
}

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

在可编码部分中添加某种桥接，

我想要归档的是类似于：

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 {
...
}

我能和Codable一起做这个吗？

Answer 1

合理的解决方案是具有相关值的枚举，因为类型可以由productype键确定。init方法首先用CodingKey对productype进行解码，然后在switch中(从singleValueContainer(进行解码，并将正确的类型/值与相应的情况相关联。

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",
"name": "name",
"propertyOfA": "12",
"productype": "a"
},
{
"id": "3",
"name": "name",
"propertyOfA": "1243",
"productype": "a"
},
{
"id": "1",
"name": "name",
"propertyOfB": "1243",
"productype": "b"
},
{
"id": "1",
"name": "name",
"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。