我如何解码 JSON 可变类型的数据字段？

Question

我从 API 接收 JSON 数据，但有些字段有时是字符串，有时是整数。此类问题的最佳解决方案是什么？

这是我的解码代码：

public struct Nutriments {
    public let energy: String?
    public let energyServing: String?
    public let energy100g: String?

    public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        energy = try container.decodeIfPresent(String.self, forKey: .energy)
        energy100g = try container.decodeIfPresent(String.self, forKey: .energy100g)
        energyServing = try container.decodeIfPresent(String.self, forKey: .energyServing)
        }
}

JSON 示例：

"nutriments": {
        "energy_100g": 8.97,
        "energy_serving": "55",
        "energy": "7"
}

其他时间是这样的：

"nutriments": {
        "energy_100g": "8.97",
        "energy_serving": 55,
        "energy": 7
}

Answer 1

首先责怪服务的所有者发送不一致的数据。

要解码这两种类型，您可以在 init 方法中检查类型。

至少 API 似乎发送了所有键，因此您可以将所有结构成员声明为非可选

public struct Nutriments {

    public let energy: String
    public let energyServing: String
    public let energy100g: String

    public init(from decoder: Decoder) throws {      
        let container = try decoder.container(keyedBy: CodingKeys.self)
        do { energy = try container.decode(String.self, forKey: .energy) }
        } catch DecodingError.typeMismatch { energy = String(try container.decode(Int.self, forKey: .energy)) }
        do { energy100g = try container.decode(String.self, forKey: .energy100g) }
        } catch DecodingError.typeMismatch { energy100g = String(try container.decode(Int.self, forKey: .energy100g)) }
        do { energyServing = try container.decode(String.self, forKey: .energyServing) }
        } catch DecodingError.typeMismatch { energyServing = String(try container.decode(Int.self, forKey: .energyServing)) }
    }
}

Answer 2

一个解决方案是在 Double 上声明一个自定义包装器，它知道如何从字符串或双精度数中解码自己：

struct DoubleLike: Decodable {
    public let value: Double

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        do {
            value = try container.decode(Double.self)
        } catch DecodingError.typeMismatch {
            let valueString = try container.decode(String.self)
            if let dbl = Double(valueString) {
                value = dbl
            } else {
                throw DecodingError.dataCorrupted(.init(codingPath: [], debugDescription: "Could not convert \(valueString) to Double"))
            }
        }
    }
}

您可以在您的结构中轻松使用它：

struct Nutriments: Decodable {
    public let energy: DoubleLike
    public let energyServing: DoubleLike
    public let energy100g: DoubleLike

    enum CodingKeys: String, CodingKey {
        case energy
        case energyServing = "energy_serving"
        case energy100g = "energy_100g"
    }
}

此解决方案的优点是可扩展，缺点是您总是需要提取 .value 属性才能使用解码后的双精度。

另一种解决方案是编写您自己的 Decoder 实现，但这可能不值得付出努力。

我如何解码 JSON 可变类型的数据字段？

How can i decode JSON data field that are of changeable types?

api

json

swift

decodable