Check for JSON Object Key before casting to a Codable in Swift 4

Question

My company's API is.... unique. The only thing that is 100% is that all responses are encapsulated in a myCompany object. And then either in a Data object or an Errors object. After that it's pretty much fair game. I am working with our head API developer, but it's a slow change because the code was written 10 years ago etc.. etc..

{ "myCompany": {
        "Errors": [{
            //Various error message key/values based upon who ever created it
        }]
    }
}


{ "myCompany": {
        "Data": {
            //any key/value of arrays and objects that I want to turn into a Codable
        }
    }
}

Is there a way for me to test if a root level key exists before I try to JSON Decode into a Codeable Struct? I hope that makes sense.

For example if the json data has the root level key of jsonData["myCompany"]["Data"] and MySpecialClass is what requested it, I could just send the value of jsonData["myCompany"]["Data"] to MySpecialClass so it can json decode

let mydata = try? JSONDecoder().decode(MySpecialClassData.self, from: jsonData["myCompany"]["Data"])

It use to be in Objective-C I could just test for the keys in a dictionary to accomplish this. I don't know to this in Swift yet.

do {
    guard let jsonData = try JSONSerialization.jsonObject(with: urlSessionDataTaskResponse, options: [.allowFragments]) as? [[String:Any]] else  {
    print("Error jsonData was not in the correct format. Surprise. Surprise.");
    if let str = String(data: dataResponse, encoding: String.Encoding.utf8) {
        print("Raw Data: \(str)")
    }
        return
    }

    // Something like this
    // if   jsonData["myCompany"]["Data"]     
    // else if  jsonData["myCompany"]["Errors"]     
    // else who knows throw an error            

  ///I have tried But this doesn't seem to work
 guard let myCompany = jsonData["myCompany"] as? [String:Any] else { return }

} catch {
    print("ERROR: \(error)")
}

All of the tutorials I have seen require me to put the data into a Codable before doing any.

Any thoughts?

https://stackoverflow.com/questions/46740160/swift-decodable-optional-key You can have `struct MyCompanyCodableStruct { errors: [MySpecialStructError]?; data: MySpecialStructData?}`. — Larme, Oct 17 '18 at 13:34
do you have all the sub json decoded correctly ? in case its an error or not ? — Mohmmad S, Oct 17 '18 at 13:34

score 2 · Answer 1 · answered Oct 17 '18 at 13:38

In case that you have constructed the Error correctly and the Data correctly you can use both of them inside a parent struct as optionals and decode that, your code could be looking like this

struct ParentResponse: Codable {
data: MySpecialClassData?
error: MySpecialErrorData?  // or an array of it would be like this [MySpecialErrorData]?

}

Now you can decode this ParentResponse and check if the data was decoded or not by checking if its nil value simply optional chaining.

So in your case one of them has to be nil, simply check if error was nil then use data, else check out what is the error — Mohmmad S, Oct 17 '18 at 13:39

score 0 · Answer 2 · answered Oct 17 '18 at 13:55

Your response is a dictionary which is [String:Any], but you try to decode it with a dictionary array [[String:Any]]. Inside your response there is another dictionary, with a key of "Errors" or "Data" depending of the situation.

guard let jsonData = try JSONSerialization.jsonObject(with: urlSessionDataTaskResponse, options: [.allowFragments]) as? [String:Any] else  {
print("Error jsonData was not in the correct format. Surprise. Surprise.");
if let str = String(data: dataResponse, encoding: String.Encoding.utf8) {
        print("Raw Data: \(str)")
    }
    return
}
if let myCompany = jsonData["myCompany"] as? [String : Any]{
    if let data = myCompany["Data"] as? [Any]{
        //you get your data
    }
    else if let errors = myCompany["Errors"] as? [Any]{
        //you get your errors
    }
}
} catch {
print("ERROR: \(error)")
}

This should work.

score 0 · Answer 3 · answered Apr 08 '19 at 10:59

encode the data to dictionary:

extension Encodable {
    var dictionary: [String: Any]? {
        guard let data = try? JSONEncoder().encode(self) else { return nil}
        return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap{ $0 as? [String: Any]}
    }
}

get our object reflection:

protocol DataProtocol: Codable {
    func getMirror() -> Mirror
}
extension DataProtocol {
    func getMirror() -> Mirror {
        return Mirror(reflecting: self)
    }
}

// some object:
struct dateModal: DataProtocol {
    var name: String?
    var age: Int?
}

//return false if key not found in json:
private func keyValidation<T: DataProtocol>(with dataModel: T?) -> Bool {
    guard let dictionaryModel = dataModel.dictionary, let mirror = dataModel?.getMirror() else { return false }
    for attr in mirror.children {
        guard dictionaryModel[attr.label ?? ""] != nil else { return false }
    }
    return true
}

//decode the data:

.....
let dataModel = try JSONDecoder().decode(AnyClass, from: data)

//then check for the key:

guard keyValidation(with: dataModel) else { return }

artyom.razinov · Answer 4 · 2020-05-14T14:40:34.517

I like when API is structured (like described here for example: https://medium.com/makingtuenti/indeterminate-types-with-codable-in-swift-5a1af0aa9f3d), however, some APIs are not, but you can make an intermediate class that include every field and then cast it to an enum:

public final class MyCompanyResponseUnion: Decodable {
    public let error: Error?
    public let data: Data?
    public let otherData: Data?

    public func toEnum() -> MyCompanyResponse {
        if let error = error {
            return MyCompanyResponse.failure(
                MyCompanyResponse.Failure(
                    error: error
                )
            )
        } else if let data = data { // e.g. if `otherData` is optional and `data` is not
            return MyCompanyResponse.success(
                MyCompanyResponse.Success(
                    data: data,
                    otherData: otherData
                )
            )
        }
    }
}

Check for JSON Object Key before casting to a Codable in Swift 4

4 Answers4