动态 Codable 模型，在运行时绑定

Question

Codable 结构创建，根据响应解码，响应上的一些键。但是 api 响应发送的密钥决定了在父 json 中使用的模型。如何在内部访问它：下面的演示代码..

如果值为“First”，那么我想使用 BodyResponse1，在所有其他情况下使用 BodyResponse2

public protocol BodyResponse: Codable { }

struct BodyResponse1: BodyResponse {
    let title_1: String
    let description_1: String
}

struct BodyResponse2: BodyResponse {
    let title_2: String
    let description_2: String
}

struct BaseModel {
    let key: String
    let child_model: ChildModel?
}


struct ChildModel {
    let body: BodyResponse?

    enum CodingKeys: String, CodingKey {
        case body
    }
    
    public init(from decoder: Decoder) throws {
        
        let container = try decoder.container(keyedBy: CodingKeys.self)

        let value = "" // access the value for key in base model: how
        if value == "First" {
            body = try? BodyResponse1.init(from: container.superDecoder(forKey: .body))
        } else {
            body = try? BodyResponse2.init(from: container.superDecoder(forKey: .body))
        }
    }
}

示例 json：

{
  "key": "First",
    "child_model": {
      "body": {
        "title_1": "",
        "description_1": ""
      },
      "random_key": 12
    }
}

{
  "key": "Second",
    "child_model": {
      "body": {
        "title_2": "",
        "description_2": ""
      },
      "random_key": 12
    }
}

Answer 1

您可以查看BaseModel中的密钥。使用nestedContainer 获取子模型的容器。

struct BaseModel: Codable {
    let key: String
    let childModel: ChildModel?
    
    enum CodingKeys: String, CodingKey {
        case key, childModel = "child_model"
    }
    
    enum ChildCodingKeys: CodingKey {
        case body
    }
    
    public init(from decoder: Decoder) throws {
        
        let container = try decoder.container(keyedBy: CodingKeys.self)
        key = try container.decode(String.self, forKey: .key)
        let childContainer = try container.nestedContainer(keyedBy: ChildCodingKeys.self, forKey: .childModel)
        if key == "First" {
            childModel = ChildModel(body: try childContainer.decode(BodyResponse1.self, forKey: .body))
        } else if key == "Second" {
            childModel = ChildModel(body: try childContainer.decode(BodyResponse2.self, forKey: .body))
        } else {
            throw DecodingError.dataCorruptedError(forKey: .body, in: childContainer, debugDescription: "Unknown body response")
        }
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(key, forKey: .key)
        var childContainer = container.nestedContainer(keyedBy: ChildCodingKeys.self, forKey: .childModel)
        if let response1 = childModel?.body as? BodyResponse1 {
            try childContainer.encode(response1, forKey: .body)
        } else if let response2 = childModel?.body as? BodyResponse2 {
            try childContainer.encode(response2, forKey: .body)
        } else {
            throw EncodingError.invalidValue(childModel?.body as Any, .init(codingPath: childContainer.codingPath, debugDescription: "Unknown body response type"))
        }
    }
}

// you might want to move "body" into BaseModel if ChildModel only has this one property.
struct ChildModel {
    let body: BodyResponse?
}