Implementing CoreData in your iOS app and CRUD’ing data.
1. Adding Coredata + xcdatamodel
When creating a new project simply make sure to include CoreData storage. Xcode will handle setting up CoreData in your project and will create the xcdatamodel for you.
If you are adding CoreData to an existing project, in this case, simply create a new xcdatamodel file:
New File -> Data Model
Also add the following code to your AppDelegate.swift:
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentContainer = {
/*
The persistent container for the application. This implementation
creates and returns a container, having loaded the store for the
application to it. This property is optional since there are legitimate
error conditions that could cause the creation of the store to fail.
*/
let container = NSPersistentContainer(name: "ExampleCoreDataProject")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
/*
Typical reasons for an error here include:
* The parent directory does not exist, cannot be created, or disallows writing.
* The persistent store is not accessible, due to permissions or data protection when the device is locked.
* The device is out of space.
* The store could not be migrated to the current model version.
Check the error message to determine what the actual problem was.
*/
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()
// MARK: - Core Data Saving support
func saveContext () {
let context = persistentContainer.viewContext
if context.hasChanges {
do {
try context.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}
Also add self.saveContext() to the applicationWillTerminate(_ application: UIApplication) method.
Don’t forget to change the title of the container "ExampleCoreDataProject" with the title of your iOS app
If your app has a dash in the name, such as: some-app, the container name will need to be some_app.
2. Create an entity
Create an entity in your xcdatamodel class, implement a similar class in code, such as the snippet below.
Note that the entityTitle is the title given to the entity in the xcdatamodel:
import Foundation
public struct SerializedToken: Equatable, Codable {
static let entityTitle = "Token"
var label: String
var secret: Data
var algorithm: String
var digitAmount: Int
var code: String
var issuer: String
init(label: String, secret: Data, algorithm: String, code: String, issuer: String, digitAmount: Int) {
self.label = label
self.issuer = issuer
self.algorithm = algorithm
self.digitAmount = digitAmount
self.code = code
self.secret = secret
}
init(from token: Token) {
self.label = token.label
self.issuer = token.issuer
self.algorithm = token.algorithm.rawValue
self.digitAmount = token.digitAmount
self.code = String(token.code.toString())
self.secret = token.secret
}
}
3. Error handling (optional)
A small enum for error handling which can be applied to your CoreData methods to handle certain exceptions. Modify it accordingly to your criteria.
public enum CoreDataError: Swift.Error {
case duplicateItem(String)
case itemDoesNotExist
case unknownError
}
4. CRUD
Implement the following pieces of code to CRUD coredata. Naturally you will need to modify them according to your models. In case you are wondering how to retrieve the NSManagedObjectContext, you can check here.
Create
import CoreData
public class func saveToken(_ serializedtoken: SerializedToken, using context: NSManagedObjectContext) throws {
guard !itemAlreadyExists(serializedtoken, using: context) else {
throw CoreDataError.duplicateItem(serializedtoken.label)
}
let entity = NSEntityDescription.entity(forEntityName: SerializedToken.entityTitle, in: context)
let newToken = NSManagedObject(entity: entity!, insertInto: context)
newToken.setValue(serializedtoken.label, forKey: "label")
newToken.setValue(serializedtoken.issuer, forKey: "issuer")
newToken.setValue(serializedtoken.algorithm, forKey: "algorithm")
newToken.setValue(serializedtoken.code, forKey: "code")
newToken.setValue(serializedtoken.secret, forKey: "secret")
newToken.setValue(serializedtoken.digitAmount, forKey: "digitamount")
try! context.save()
}
Also a method to see if an item already exists within storage by a self-defined predicate:
import CoreData
public class func itemAlreadyExists(_ token: SerializedToken, using context: NSManagedObjectContext) -> Bool {
let request = NSFetchRequest<NSFetchRequestResult>(entityName: SerializedToken.entityTitle)
request.predicate = NSPredicate(format: "secret = %@ AND label = %@ AND algorithm =%@", token.secret as CVarArg, token.label, token.algorithm)
request.returnsObjectsAsFaults = false
if let result = try? context.fetch(request) {
let foundItems = result as! [NSManagedObject]
return foundItems.count > 0
} else {
return false
}
}
Reading
import CoreData
public class func getTokens(context: NSManagedObjectContext) throws -> [SerializedToken] {
let request = NSFetchRequest<NSFetchRequestResult>(entityName: SerializedToken.entityTitle)
request.returnsObjectsAsFaults = false
let result = try! context.fetch(request)
var tokenResult = [[SerializedToken]()
for data in result as! [NSManagedObject] {
tokenResult.append(SerializedToken(
label: data.value(forKey: "label") as! String,
secret: data.value(forKey: "secret") as! Data,
algorithm: data.value(forKey: "algorithm") as! String,
code: data.value(forKey: "code") as! String,
issuer: data.value(forKey: "issuer") as! String,
digitAmount: data.value(forKey: "digitamount") as! Int)
)
}
return tokenResult
}
Update
import CoreData
public class func updateToken(_ serializedToken: SerializedToken, with updatedToken:SerializedToken, using context: NSManagedObjectContext) throws {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: SerializedToken.entityTitle)
fetchRequest.predicate = NSPredicate(format: "secret = %@ AND label = %@ AND algorithm =%@", serializedToken.secret as CVarArg, serializedToken.label, serializedToken.algorithm)
fetchRequest.returnsObjectsAsFaults = false
if let result = try? context.fetch(fetchRequest) {
let foundItems = result as! [NSManagedObject]
guard foundItems.count > 0 else {
throw CoreDataError.itemDoesNotExist
}
let foundToken = foundItems[0]
foundToken.setValue(updatedToken.label, forKey: "label")
foundToken.setValue(updatedToken.issuer, forKey: "issuer")
try! context.save()
} else {
throw CoreDataError.unknownError
}
}
Delete
import CoreData
public class func removeToken(_ serializedToken: SerializedToken, using context: NSManagedObjectContext) throws {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: SerializedToken.entityTitle)
fetchRequest.predicate = NSPredicate(format: "secret = %@ AND label = %@ AND algorithm =%@", serializedToken.secret as CVarArg, serializedToken.label, serializedToken.algorithm)
fetchRequest.returnsObjectsAsFaults = false
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
try! context.execute(deleteRequest)
}
import CoreData
public class func removeAllTokens(using context: NSManagedObjectContext) throws {
let request = NSBatchDeleteRequest(fetchRequest: NSFetchRequest<NSFetchRequestResult>(entityName: SerializedToken.entityTitle))
try! context.execute(request)
}