When you have a Realm model that looks something like:
class Thing: Object, Decodable {
#objc dynamic var id: String = ""
#objc dynamic var propertyOne: String = ""
#objc dynamic var propertyTwo: String? = nil
override static func primaryKey() -> String? {
return "id"
}
}
All of the data is from a JSON file, using a JSON Serializer:
func serialize(input sourceName: String) {
let path = Bundle.main.path(forResource: sourceName, ofType: nil)
let url = URL(fileURLWithPath: path!)
let jsonDecoder = JSONDecoder()
do {
let data = try Data(contentsOf: url)
let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments)
guard json is [AnyObject] else {
assert(false, "failed to parse")
return
}
do {
let things = try jsonDecoder.decode([Thing].self, from: data)
let realm = try! Realm()
for thing in things {
try! realm.write {
realm.add(thing)
// realm.add(thing, update: .modified) wipes out all changes
}
}
} catch let error {
print("failed to convert data: \(error)")
}
} catch let error {
print(error)
}
}
propertyOne's info is gotten from the JSON. propertyTwo's value is meant to be inputted from within the app. Once I serialize the JSON again, all changes to propertyTwo are wiped out. How do I make a migration without restoring it to the original JSON file? I want to keep some properties unchanged during a migration/new serialization.
In my AppDelegate, this is my code in didFinishLaunchingWithOptions:
let serializer = JSONSerializer()
serializer.serialize(input: "Nafliah.json")
This works if I have realm.add(thing, update: .modified) in my serializer. But this wipes out all changes made within the app. If I change it to this:
if save.bool(forKey: "serilized") == false {
let serializer = JSONSerializer()
serializer.serialize(input: "Nafliah.json")
save.set(true, forKey: "serilized")
}
And make the serializer part realm.add(thing), it works and does not wipe out changed data every time the app is opened.
The issue is, once I add a new object to the JSON file, it obviously does not get added to the realm. I must serialize the JSON again. This, however, deletes all changes done in the 2 properties that are only meant to be changed by the user in the app.
I figured it out. You have to do a partial serialization.
Changed this:
realm.add(thing, update: .modified)
To:
realm.create(Thing.self, value: [
"id": thing.id,
"propertyOne": thing.propertyOne
// Leave out propertyTwo to leave it unchanged
], update: .modified)
Please check below link for Migrating Realm for existing properties
https://docs.realm.io/sync/v/3.x/using-synced-realms/migrating-your-data
Related
I'm using Firebase Database and I'm attempting to retrieve and use data with NSObject. I'm receiving an NSUnknownKeyException error when running the app, causing it to crash.
NSObject:
class WatchList: NSObject {
var filmid: Int?
}
Firebase Code:
ref.child("users").child(uid!).child("watchlist").observe(DataEventType.childAdded, with: { (info) in
print(info)
if let dict = info.value as? [String: AnyObject] {
let list = WatchList()
list.setValuesForKeys(dict)
print(list)
}
}, withCancel: nil)
I'm not sure of what could cause this.
Also, to enhance this solution is their a way to take this data and, instead of using NSObject, use Codable and JSONDecoder with the Firebase data?
You can simply use JSONSerialization to convert the snapshot value property from Any to Data:
let data = try? JSONSerialization.data(withJSONObject: snapshot.value)
You can also extend Firebase DataSnapshot type and add a data and json string properties to it:
import Firebase
extension DataSnapshot {
var data: Data? {
guard let value = value, !(value is NSNull) else { return nil }
return try? JSONSerialization.data(withJSONObject: value)
}
var json: String? { data?.string }
}
extension Data {
var string: String? { String(data: self, encoding: .utf8) }
}
usage:
guard let data = snapshot.data else { return }
It's 2021 now.
Firebase finally added support for decoding Firestore documents. Just let your objects conform to Codable and decode like this:
let result = Result {
try document?.data(as: City.self)
}
switch result {
case .success(let city):
if let city = city {
print("City: \(city)")
} else {
print("Document does not exist")
}
case .failure(let error):
// A `City` value could not be initialized from the DocumentSnapshot.
print("Error decoding city: \(error)")
}
Just don't forget to add the 'FirebaseFirestoreSwift' pod and then import it into your file.
Read more:
https://firebase.google.com/docs/firestore/query-data/get-data#custom_objects
Original answer
A really nice library to use here is Codable Firebase which I am also using in my project. Just make your class / struct conform to Codable protocol and use FirebaseDecoder to decode your Firebase data into a Swift object.
Example:
Database.database().reference().child("model").observeSingleEvent(of: .value, with: { snapshot in
guard let value = snapshot.value else { return }
do {
let model = try FirebaseDecoder().decode(Model.self, from: value)
print(model)
} catch let error {
print(error)
}
})
This is too simple but I am lost. I am still new to swift really.
I need to parse the downloaded json ( localized file in the Xcode project ) and populate the data to a CollectionView.
enum Response{
case success(Data)
case error(Error)
}
// struct follows the json
struct InformationFromJson: Decodable {
let id: Int
let name: String
}
class MYJSON {
public func downloadMYJSON(_ completion: #escaping (Response) -> ()) {
guard let bundle = Bundle(identifier: MYJSON.bundleId), let path = bundle.path(forResource: "data", ofType: "json"), let data = try? Data(contentsOf: URL(fileURLWithPath: path)) else {
completion(Response.error(NSError(domain: MYJSON.bundleId, code: MYJSON.bundleErrorCode, userInfo: [NSLocalizedDescriptionKey : MYJSON.bundleError])))
return
}
completion(Response.success(data))
}
}
So, without totally changing the function call, how do I parse the json? It's downloaded so far from the function, but I don't see how to even add a print statement to test, without getting errors because of the guard statement , the way it is.
I need to simple populate a cellForRowAt:
I never saw nested guard like this, so it got me. I am used to seeing the let statements separated so you can put print statements to at least see if things are getting downloaded or parsed.
You can decode your json by passing data, whatever you get from
let data = try? Data(contentsOf: URL(fileURLWithPath: path))
guard let decoded = try? JSONDecoder().decode(InformationFromJson.self, from: data) else {
return
}
I'm using the SocketIO library to connect my iOS app to my server.
I want to emit some data to the server and get a json dictionary back in the acknowledgment. I currently have something like this:
SocketHandler.mySocket.emitWithAck("my_event", [session, someInput]).timingOut(after: 3) {data in
let myData = try? JSONDecoder().decode(myStruct.self, from: data)
MyStruct is defined as Class inheriting from Decodable and resembles the structure of the json I expect.
I get the following error: Cannot convert value of type 'Any' to expected argument type 'Data'
Any idea how I can tackle that type casting? Or would I need to go a totally other route?
(Swift 4.1 for iOS 11.3)
Cheers!
If anyone else is wondering how to use SocketIO with Decodable, I created a little extension for the client to accept Decodable in the callback, based on Dan Karbayev's answer.
import Foundation
import SocketIO
extension Decodable {
init(from any: Any) throws {
let data = try JSONSerialization.data(withJSONObject: any)
self = try JSONDecoder().decode(Self.self, from: data)
}
}
extension SocketIOClient {
func on<T: Decodable>(_ event: String, callback: #escaping (T)-> Void) {
self.on(event) { (data, _) in
guard !data.isEmpty else {
print("[SocketIO] \(event) data empty")
return
}
guard let decoded = try? T(from: data[0]) else {
print("[SocketIO] \(event) data \(data) cannot be decoded to \(T.self)")
return
}
callback(decoded)
}
}
}
Usage:
socket.on("location") { (data: LocationEventData) in
// ...
}
socket.on("success") { (name: String) in
// ...
}
Where LocationEventData and String are Decodable.
There're two things:
decode(_:from:) accepts a Data as a second parameter. To be able to decode from Any you'll need to add an extension to first serialize the data and then pass it to JSONDecoder, like this:
extension Decodable {
init(from any: Any) throws {
let data = try JSONSerialization.data(withJSONObject: any)
self = try JSONDecoder().decode(Self.self, from: data)
}
}
AckCallback's parameter is of an array type (i.e. [Any]), so you should get the first element of that array.
To make sure that you have indeed a decodable data (a dictionary or a JSON object) you can write something like this:
SocketHandler.mySocket.emitWithAck("my_event", [session, someInput]).timingOut(after: 3) { data in
guard let dict = data.first as? [String: Any] else { return }
let myData = try? myStruct(from: dict)
// ...
}
As a part of teaching myself Swift, I am working on a Weather App. I am currently attempting to integrate weather alerts. I use a struct called AlertData to initialize data returned from the API call to weather.gov after serializing the returned data from an API call. Or, at least that is the plan. I have modeled my classes off of other classes that request data from weather.gov, but to get an alert, I need to be able to send variable parameters in my dataTask. I use the URL extension from Apple's App Development with Swift (code below) and have the code set to issue the parameters with the users current location to get alerts where the user is currently.
My problem comes when I attempt to construct the API call to weather.gov in my AlertDataController class(code below). Xcode keeps throwing different errors and I am not sure why. I would like to use a guard statement as I have in my code below, but that throws an error of "Cannot force unwrap value of non-optional type '[[String : Any]]'" in my code where shown. It also throws the same error when I make it a simple constant assignment after unwrapping as the extension returns an optional URL.
The same code works flawlessly when I construct the URL from a string in the guard statement directly as in:
guard let url = URL(string: (baseURL + locationString + stations)) else {
What am I missing? Where my error is thrown is inside the dataTask, and regardless of how it got there, the variable url is an unwrapped URL. Thanks in advance.
Controller class:
import Foundation
import CoreLocation
struct AlertDataController {
func checkWxAlert(location: CLLocation, completion: #escaping (AlertData?) -> Void) {
let baseURL = URL(string: "https://api.weather.gov/alert")!
let locationString = "\(location.coordinate.latitude),\(location.coordinate.longitude)"
var query = [
"active": "1",
"point": locationString
]
guard let url = baseURL.withQueries(query) else {
completion(nil)
print("Unable to build URL in AlertDataController.checkWxAlert with supplied queries.")
return
}
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let data = data,
let rawJSON = try? JSONSerialization.jsonObject(with: data),
let json = rawJSON as? [String: Any],
let featuresDict = json["features"] as? [[String: Any]],
let propertiesArray = featuresDict!["properties"] as? [String: Any] {
Error: Cannot force unwrap value of non-optional type '[[String : Any]]'
let alertData = AlertData(json: propertiesArray)
completion(alertData)
} else {
print("Either no data was returned in AlertDataController.checkWxAlert, or data was not serialized.")
completion(nil)
return
}
}
task.resume()
}
}
URL extension:
import Foundation
extension URL {
func withQueries(_ queries: [String: String]) -> URL? {
var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
components?.queryItems = queries.flatMap { URLQueryItem(name: $0.0, value: $0.1) }
return components?.url
}
func withHTTPS() -> URL? {
var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
components?.scheme = "https"
return components?.url
}
}
If featuresDict is really an array, you cannot use featuresDict["properties"] syntax. That subscript with string syntax is only for dictionaries. But you've apparently got an array of dictionaries.
You could iterate through the featuresDict array (which I'll rename to featuresArray to avoid confusion), you could do that after you finish unwrapping it. Or, if just want an array of the values associated with the properties key for each of those dictionaries, then flatMap is probably a good choice.
For example:
let task = URLSession.shared.dataTask(with: url) { data, _, error in
guard let data = data,
error == nil,
let json = (try? JSONSerialization.jsonObject(with: data)) as? [String: Any],
let featuresArray = json["features"] as? [[String: Any]] else {
print("Either no data was returned in AlertDataController.checkWxAlert, or data was not serialized.")
completion(nil)
return
}
let propertiesArray = featuresArray.flatMap { $0["properties"] }
let alertData = AlertData(json: propertiesArray)
completion(alertData)
}
Or, if AlertData is expecting each of those properties to be, themselves, a dictionary, you might do:
let propertiesArray = featuresArray.flatMap { $0["properties"] as? [String: Any] }
Just replace that cast with whatever type your AlertData is expecting in its array, json.
Or, if you're only interested in the first property, you'd use first rather than flatMap.
The error
Cannot force unwrap value of non-optional type '[[String : Any]]'
is very clear. It occurs because in the optional binding expression featuresDict is already unwrapped when the next condition is evaluated.
Just remove the exclamation mark
... let propertiesArray = featuresDict["properties"] as? [String: Any] {
The error is not related at all to the way the URL is created.
I am using Xcode 9.2 and Swift 4. How can I check if the returned json data is null?
Now it gives me error Type 'Any' has no subscript members at line if json[0]["data"]
var json: NSMutableArray = []
var newsArray: NSMutableArray = []
let url = URLFactory()
var data = try! NSData(contentsOf: url.getURL()) as Data
do {
json = try JSONSerialization.jsonObject(with: data, options: []) as! NSMutableArray
if json[0]["data"] {
// data is not null
}
} catch let error as NSError {
// handle error
}
My JSON returns something like this:
{
"data":
[
{
"news_id":123,
"title":"title",
"news_date":"2017-02-08 21:46:06",
"news_url":"url",
"short_description":"description",
"category_id":4,
"category_name":"Health",
"latlng":
[
{
"lat":"43.003429",
"lng":"-78.696335"
}
]
}
{ ....
}
If you're using Swift 4, I might suggest JSONDecoder:
First, define the types to hold the parsed data:
struct ResponseObject: Codable {
let data: [NewsItem]
}
struct NewsItem: Codable {
let newsId: Int
let title: String
let newsDate: Date
let newsURL: URL
let shortDescription: String
let categoryID: Int
let categoryName: String
let coordinates: [Coordinate]
// because your json keys don't follow normal Swift naming convention, use CodingKeys to map these property names to JSON keys
enum CodingKeys: String, CodingKey {
case newsId = "news_id"
case title
case newsDate = "news_date"
case newsURL = "news_url"
case shortDescription = "short_description"
case categoryID = "category_id"
case categoryName = "category_name"
case coordinates = "latlng"
}
}
struct Coordinate: Codable {
let lat: String
let lng: String
}
And then you can parse it:
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(formatter)
do {
let responseObject = try decoder.decode(ResponseObject.self, from: data)
print(responseObject.data)
} catch {
print(error)
}
Clearly, if your JSON is different, you might need to change your objects accordingly (e.g. it struck me odd that latlng was an array of coordinates). Also, you can define custom init(from:) methods if you want to convert some of these strings into numbers, but I'd rather fix the JSON, instead (why are latlng returning string values rather than numeric values).
For more information, see Encoding and Decoding Custom Types.
As an aside, I'd advise against this pattern (note, this is your network request logic, but excised of NSData):
let data = try! Data(contentsOf: url.getURL())
That will retrieve the data synchronously, which can be problematic because
the app will be frozen while the data is being retrieved resulting in a poor UX;
you risk having your app killed by the watchdog process which looks for frozen apps; and
you don't have robust error handling and this will crash if the network request fails.
I'd suggest using URLSession:
let task = URLSession.shared.dataTask(with: url.getURL()) { data, _, error in
guard let data = data, error == nil else {
print(error ?? "Unknown error")
return
}
// now parse `data` like shown above
// if you then need to update UI or model objects, dispatch that back
// to the main queue:
DispatchQueue.main.async {
// use `responseObject.data` to update model objects and/or UI here
}
}
task.resume()