Deserialize a JSON array to a Swift array of objects

Question

I am new to Swift, and am not able to figure out how to deserialize a JSON array to an array of Swift objects. I'm able to deserialize a single JSON user to a Swift user object fine, but just not sure how to do it with a JSON array of users.

Here is my User.swift class:

class User {
    var id: Int
    var firstName: String?
    var lastName: String?
    var email: String
    var password: String?

    init (){
        id = 0
        email = ""
    }

    init(user: NSDictionary) {
        id = (user["id"] as? Int)!
        email = (user["email"] as? String)!

        if let firstName = user["first_name"] {
            self.firstName = firstName as? String
        }

        if let lastName = user["last_name"] {
            self.lastName = lastName as? String
        }

        if let password = user["password"] {
            self.password = password as? String
        }
     }
}

Here's the class where I'm trying to deserialize the JSON:

//single user works.
Alamofire.request(.GET, muURL/user)
         .responseJSON { response in
                if let user = response.result.value {
                    var swiftUser = User(user: user as! NSDictionary)
                }
          }

//array of users -- not sure how to do it. Do I need to loop?
Alamofire.request(.GET, muURL/users)
         .responseJSON { response in
                if let users = response.result.value {
                    var swiftUsers = //how to get [swiftUsers]?
                }
          }

oh, I had no idea I could use that. I thought it was just for REST. I'm going to give it a try. — Prabhu
– Prabhu, Commented May 10, 2016 at 22:00
Also, email is a required field for User. Is it best practice to leave it as required field in Swift, or would it be better to make it an Optional--in case the JSON does not have the value for whatever reason? — Prabhu
– Prabhu, Commented May 10, 2016 at 22:03

Alaeddine · Accepted Answer · 2016-05-10 22:05:00Z

2

The best approach is the use Generic Response Object Serialization provided by Alamofire here is an example :

1) Add the extension in your API Manager or on a separate file

    public protocol ResponseObjectSerializable {
        init?(response: NSHTTPURLResponse, representation: AnyObject)
    }

    extension Request {
        public func responseObject<T: ResponseObjectSerializable>(completionHandler: Response<T, NSError> -> Void) -> Self {
            let responseSerializer = ResponseSerializer<T, NSError> { request, response, data, error in
                guard error == nil else { return .Failure(error!) }

                let JSONResponseSerializer = Request.JSONResponseSerializer(options: .AllowFragments)
                let result = JSONResponseSerializer.serializeResponse(request, response, data, error)

                switch result {
                case .Success(let value):
                    if let
                        response = response,
                        responseObject = T(response: response, representation: value)
                    {
                        return .Success(responseObject)
                    } else {
                        let failureReason = "JSON could not be serialized into response object: \(value)"
                        let error = Error.errorWithCode(.JSONSerializationFailed, failureReason: failureReason)
                        return .Failure(error)
                    }
                case .Failure(let error):
                    return .Failure(error)
                }
            }

            return response(responseSerializer: responseSerializer, completionHandler: completionHandler)
        }
    }

public protocol ResponseCollectionSerializable {
    static func collection(response response: NSHTTPURLResponse, representation: AnyObject) -> [Self]
}

extension Alamofire.Request {
    public func responseCollection<T: ResponseCollectionSerializable>(completionHandler: Response<[T], NSError> -> Void) -> Self {
        let responseSerializer = ResponseSerializer<[T], NSError> { request, response, data, error in
            guard error == nil else { return .Failure(error!) }

            let JSONSerializer = Request.JSONResponseSerializer(options: .AllowFragments)
            let result = JSONSerializer.serializeResponse(request, response, data, error)

            switch result {
            case .Success(let value):
                if let response = response {
                    return .Success(T.collection(response: response, representation: value))
                } else {
                    let failureReason = "Response collection could not be serialized due to nil response"
                    let error = Error.errorWithCode(.JSONSerializationFailed, failureReason: failureReason)
                    return .Failure(error)
                }
            case .Failure(let error):
                return .Failure(error)
            }
        }

        return response(responseSerializer: responseSerializer, completionHandler: completionHandler)
    }
}

2) update your model object like this:

final class User: ResponseObjectSerializable, ResponseCollectionSerializable {
    let username: String
    let name: String

    init?(response: NSHTTPURLResponse, representation: AnyObject) {
        self.username = response.URL!.lastPathComponent!
        self.name = representation.valueForKeyPath("name") as! String
    }

    static func collection(response response: NSHTTPURLResponse, representation: AnyObject) -> [User] {
        var users: [User] = []

        if let representation = representation as? [[String: AnyObject]] {
            for userRepresentation in representation {
                if let user = User(response: response, representation: userRepresentation) {
                    users.append(user)
                }
            }
        }

        return users
    }
}

3) then you can use it like that :

Alamofire.request(.GET, "http://example.com/users")
         .responseCollection { (response: Response<[User], NSError>) in
             debugPrint(response)
         }

Source: Generic Response Object Serialization

Useful Link: Alamofire JSON Serialization of Objects and Collections

edited May 10, 2016 at 22:05

answered May 10, 2016 at 22:02

Alaeddine

6,2123 gold badges31 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Prabhu Over a year ago

Thanks, will give this a try!

Alaeddine Over a year ago

I used that in my last project and I find it an elegant solution, because mapping is already a feature in Almofire, and it's better to not delay to other third party library to avoid any compatibility issues in the future

Prabhu Over a year ago

How do I deal with an optional field? Say it was: let name: String?

dydus0x14 Over a year ago

Binding from JSON shouldn't be a part of Model. Using protocol extension of model's classes like this 'protocol ResponseObjectSerializable' is not a good idea because in this case you cannot use different variants of parsing to User object. There is new library for Swift JSON binding and validating - Bender github.com/ptiz/bender which excludes such mistakes.

Alaeddine Over a year ago

@Prabhu you can use self.name = representation.valueForKeyPath("name") as? String

kallahir · Accepted Answer · 2016-05-10 22:46:20Z

2

Since you are using Alamofire to make your requests why don't you give a chance to Hearst-DD ObjectMapper it has an Alamofire extension AlamofireObjectMapper. I think it'll save you time!

answered May 10, 2016 at 22:46

kallahir

214 bronze badges

1 Comment

Prabhu Over a year ago

Looks interesting.

Echizzle · Accepted Answer · 2016-05-10 22:05:59Z

1

I would loop through them then add each user to an array (preferably a property of the VC and not an instance variable) but here is an example.

    Alamofire.request(.GET, "YourURL/users")
        .responseJSON { response in

            if let users = response.result.value {

                for user in users {

                    var swiftUser = User(user: user as! NSDictionary)

                    //should ideally be a property of the VC
                    var userArray : [User]

                    userArray.append(swiftUser)
                }
            }
    }

answered May 10, 2016 at 22:05

Echizzle

3,4795 gold badges19 silver badges28 bronze badges

4 Comments

Echizzle Over a year ago

I'm not exactly sure how the JSON looks from the response so you might need to tweak it a bit but this should give you an idea at least.

Prabhu Over a year ago

With this method I get an error saying Type AnyObject does not conform to protocol SequenceType. Any idea what that is?

Echizzle Over a year ago

Try changing the for loop to "for user in users as! [AnyObject]" instead of just "for user in users"

dydus0x14 Over a year ago

Using as! [AnyObject] or user as! NSDictionary is not so safe. if let users = response.result.value as? [String: AnyObject] { is more Swifty way.

parbo · Accepted Answer · 2017-02-15 19:28:33Z

1

You could also try EVReflection https://github.com/evermeer/EVReflection It's even more simple, i.e. to parse JSON (code snippet taken from EVReflection link):

let json:String = "{
    \"id\": 24, 
    \"name\": \"Bob Jefferson\",
    \"friends\": [{
        \"id\": 29, 
        \"name\": 
        \"Jen Jackson\"}]}"

you can use this class:

class User: EVObject {
    var id: Int = 0
    var name: String = ""
    var friends: [User]? = []
}

in this way:

let user = User(json: json)

answered Feb 15, 2017 at 19:28

parbo

2533 silver badges8 bronze badges

Collectives™ on Stack Overflow

Deserialize a JSON array to a Swift array of objects

4 Answers 4

5 Comments

1 Comment

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

1 Comment

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related