Decode data of Object type and generic type for base JSON response using Decodable

Question

I have a base model -

struct BaseModel<T:Decodable>: Decodable {
    let jsonData: [T]?
    let status: Bool?
    let message: String?
    
    enum CodingKeys: String, CodingKey {
        case jsonData = "data"
        case status = "success"
        case message
    }
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        do {
            if let string = try container.decodeIfPresent(T.self, forKey: .jsonData) {
                print(string)
                jsonData = [string]
            } else {
                jsonData = nil
            }
        } catch DecodingError.typeMismatch {
            jsonData = try container.decodeIfPresent([T].self, forKey: .jsonData)
        }
        status = try container.decodeIfPresent(Bool.self, forKey: .status)
        message = try container.decodeIfPresent(String.self, forKey: .message)
    }
}

I am getting response in two types under jsonData

Object
Array

Getting error while decoding if I receive response as Object. And if I choose let jsonData: T?, Then getting issue in decoding of Array response.

I am using this model in my Network Model. That looks like -

    func performOperation<T:Decodable>(urlEndPoint: String, method: HTTPMethod, param: Parameters?, isJsonAvailable: Bool, completion: @escaping(_ response: T?, [T]?, String?, Bool?) ->Void) {
        AF.request(urlEndPoint, method: method, parameters: param, headers: header).validate(statusCode: 200..<500).responseDecodable(of: BaseModel<T>.self, decoder: decoder) { (response) in
}

Json response in case of Object -

  {
    "success": true,
    "data": {
        "heading": "Same text 1",
        "title": "Sample Text 2",
        "content": "Sample text 3"
    },
    "message": "Api response received"
}

Json response in case of ArrayList -

{
    "success": true,
    "data": [
        {
            "id": 1,
            "name": "Home"
        },
        {
            "id": 2,
            "name": "Profile"
        }
    ],
    "message": "Menu List"
}

Show your Object and your Array types. Also show your JSON response. — Leo Dabus
– Leo Dabus, Commented Aug 28, 2020 at 12:53
Also please post the error that you are getting from JSONDecode. — gcharita
– gcharita, Commented Aug 28, 2020 at 13:02
@gcharita, Seems Like working with my own above code 😃 Thanks for you constant support. Much appreciated, Will let you know if I face any issue. — Shashi Tiwari
– Shashi Tiwari, Commented Aug 28, 2020 at 13:33

Leo Dabus · Accepted Answer · 2020-08-28 13:51:28Z

You don't need a generic structure. Just create a optional property to assign your object in case there is no user array:

struct BaseModel {
    let data: [User]
    let post: Post?
    let success: Bool
    let message: String
}

struct User: Codable {
    let id: Int
    let name: String
}

struct Post: Codable {
    let heading: String
    let title: String
    let content: String
}

extension BaseModel: Codable  {
    init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            do {
                data = try container.decode([User].self, forKey: .data)
                post = nil
            } catch DecodingError.typeMismatch {
                data = []
                post = try container.decode(Post.self, forKey: .data)
            }
            success = try container.decode(Bool.self, forKey: .success)
            message = try container.decode(String.self, forKey: .message)
        }
}

If there is other responses not shown in your post you can do the same approach above using a generic structure as well:

struct BaseModel<T: Codable> {
    let array: [T]
    let element: T?
    let success: Bool
    let message: String
}

extension BaseModel: Codable  {
    init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            do {
                array = try container.decode([T].self, forKey: .array)
                element = nil
            } catch DecodingError.typeMismatch {
                array = []
                element = try container.decode(T.self, forKey: .array)
            }
            success = try container.decode(Bool.self, forKey: .success)
            message = try container.decode(String.self, forKey: .message)
        }
}

In my current code its working as expected, Now I don't need to convert object type in array. Thanks. @Leo Dabus

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