Get Core Data Entity relatives with a generic function - swift

I'm designing a data manager for my Core Data model and I'd like to create a generic function to fetch relatives of a class.
I’ve created a protocol allowing to build managers for each data type. In this protocol I already defined two associated types T and K and several simple functions. Now I’m stuck with a class relatives fetching method — I need to indicate somehow that T has K relatives. I’ve tried in vain to create some protocol indicating this relationship thru mutual properties, so both classes could conform to this protocol. Any idea, is it even possible?
import Foundation
import CoreData
protocol DataManager {
associatedtype T: NSManagedObject, NSFetchRequestResult
associatedtype K: NSManagedObject, NSFetchRequestResult // Relative
static var sharedInstance: Self { get }
static func getAll(sorted: [NSSortDescriptor]?, context: NSManagedObjectContext) -> [T]?
static func insert(item: T)
static func update(item: T)
static func clean()
static func deleteById(id: String)
// Relatives
static func getRelatives(by: T) -> [K]?
static func get(byRelative: K) -> [T]?
}
extension DataManager {
static func getAll(sorted: [NSSortDescriptor]?, context: NSManagedObjectContext) -> [T]? {
guard let fetchRequest: NSFetchRequest<T> = T.fetchRequest() as? NSFetchRequest<T> else { return nil }
fetchRequest.sortDescriptors = sorted
var results: [T]? = nil
do {
results = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
return results
}
}
protocol Identifiable {
typealias Identity = String
var id: Identity? { get }
}
extension DataManager where Self.T: Identifiable {
static func get(by id: T.Identity, context: NSManagedObjectContext) -> T? {
guard let fetchRequest: NSFetchRequest<T> = T.fetchRequest() as? NSFetchRequest<T> else { return nil }
fetchRequest.predicate = NSPredicate(format: "%K == %#", "id", id)
var rawResults: [T]? = nil
do {
rawResults = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
if let result = rawResults?.first {
return result }
else { return nil }
}
}

Well, I've created one solution.
We can identify all relations with a particular class:
let relationships = T.entity().relationships(forDestination: K.entity())
It allows us to find all IDs of an item for each relationship (we can have many relationships for the same relative Entity):
let relativesIDs = item.objectIDs(forRelationshipNamed: relationship.name)
So, we can use these IDs to fetch records from another class.
static func getRelatives(of item: T, context:NSManagedObjectContext) -> [K]? {
guard let fetchRequest: NSFetchRequest<K> = K.fetchRequest() as? NSFetchRequest<K> else { return nil }
fetchRequest.fetchBatchSize = 100
var results: [K]? = nil
var resultSet: Set<K> = [] // doesn't allow duplicates
let relationships = T.entity().relationships(forDestination: K.entity())
for relationship in relationships {
let relativesIDs = item.objectIDs(forRelationshipNamed: relationship.name)
let predicate = NSPredicate(format: "self IN %#", relativesIDs)
fetchRequest.predicate = predicate
var batchResults: [K] = []
do {
batchResults = try context.fetch(fetchRequest)
} catch {
assert(false, error.localizedDescription)
} //TODO: Handle Errors
if batchResults.count > 0 { resultSet = resultSet.union(Set(batchResults)) }
}
if resultSet.count > 0 { results = Array(resultSet) }
return results
}
I'm not sure that this is the most elegant solution, but it works :-)

Related

Core Data: Generic class function to return object

I have several classes of base type NSManagedObject and each of them contains a class function to return the first object of a given context. Here's an example:
public class Car: NSManagedObject {
class func first(context: NSManagedObjectContext) -> Car? {
let fetchRequest = Car.fetchRequest()
fetchRequest.fetchLimit = 1
let results = try? context.fetch(fetchRequest)
return results?.first
}
}
Instead of writing this function for every subclass I'd like to put a generic version as an extension to NSManagedObject. I've tried this:
extension NSManagedObject {
class func first(context: NSManagedObjectContext) -> Self? {
let fetchRequest = Self.fetchRequest()
fetchRequest.fetchLimit = 1
let results = try? context.fetch(fetchRequest)
return results?.first
}
}
But this gives a "Type of expression is ambigous without more context" error. How can this be done?
context.fetch() returns [Any], but you can conditionally cast it to the expected type [Self]:
extension NSManagedObject {
class func first(context: NSManagedObjectContext) -> Self? {
let fetchRequest = Self.fetchRequest()
fetchRequest.fetchLimit = 1
let results = try? context.fetch(fetchRequest) as? [Self]
return results?.first
}
}
Or with a real do/try/catch for better diagnostics in the error case:
extension NSManagedObject {
class func first(context: NSManagedObjectContext) -> Self? {
let fetchRequest = Self.fetchRequest()
fetchRequest.fetchLimit = 1
do {
let results = try context.fetch(fetchRequest) as? [Self]
return results?.first
} catch {
print(error)
return nil
}
}
}

Swift Realm Results Convert to Model

Is there any simple way to map a Realm request to a Swift Model (struct) when it is just a single row?
When it is an array of data I can do something like this and work with the array. This is not working on a single row.
func toArray<T>(ofType: T.Type) -> [T] {
return compactMap { $0 as? T }
}
But what is best to do when just a single row of data?
my databases are big so doing it manually is just a pain and ugly.
It would also be nice when the Swift Model is not 100% the same as the Realm Model. Say one has 30 elements and the other only 20. Just match up the required data.
Thank you.
On my apps I m using this class to do all actions. I hope that's a solution for your situation. There is main actions for realm.
Usage
class Test: Object {
var name: String?
}
class ExampleViewController: UIViewController {
private let realm = CoreRealm()
override func viewDidLoad() {
super.viewDidLoad()
let data = realm.getArray(selectedType: Test.self)
}
import RealmSwift
class CoreRealm {
// Usage Example:
// let testObject = RealmExampleModel(value: ["age":1 , "name":"Name"])
// let testSubObject = TestObject(value: ["name": "FerhanSub", "surname": "AkkanSub"])
// testObject.obje.append(testSubObject)
let realm = try! Realm()
func deleteDatabase() {
try! realm.write {
realm.deleteAll()
}
}
func delete<T: Object>(selectedType: T.Type) {
try! realm.write {
let object = realm.objects(selectedType)
realm.delete(object)
}
}
func delete<T: Object>(selectedType: T.Type, index: Int) {
try! realm.write {
let object = realm.objects(selectedType)
realm.delete(object[index])
}
}
func add<T: Object>(_ selectedObject: T) {
do {
try realm.write {
realm.add(selectedObject)
}
} catch let error as NSError {
print(error.localizedDescription)
}
}
// return Diretly object
func getArray<T: Object>(selectedType: T.Type) -> [T]{
let object = realm.objects(selectedType)
var array = [T]()
for data in object {
array.append(data)
}
return array
}
func getObject<T: Object>(selectedType: T.Type, index: Int) -> T{
let object = realm.objects(selectedType)
var array = [T]()
for data in object {
array.append(data)
}
return array[index]
}
// return Result tyle
func getResults<T: Object>(selectedType: T.Type) -> Results<T> {
return realm.objects(selectedType)
}
func getResult<T: Object>(selectedType: T.Type) -> T? {
return realm.objects(selectedType).first
}
func createJsonToDB<T: Object>(jsonData data: Data, formatType: T.Type) {
// let data = "{\"name\": \"San Francisco\", \"cityId\": 123}".data(using: .utf8)!
let realm = try! Realm()
try! realm.write {
do {
let json = try JSONSerialization.jsonObject(with: data, options: [])
realm.create(formatType, value: json, update: .modified)
} catch {
print("Json parsing error line 65")
}
}
}
}

Swift can't infer generic type when generic type is being passed through a parameter

I'm writing a generic wrapper class for core data.
Here are some of my basic types. Nothing special.
typealias CoreDataSuccessLoad = (_: NSManagedObject) -> Void
typealias CoreDataFailureLoad = (_: CoreDataResponseError?) -> Void
typealias ID = String
enum CoreDataResult<Value> {
case success(Value)
case failure(Error)
}
enum CoreDataResponseError : Error {
typealias Minute = Int
typealias Key = String
case idDoesNotExist
case keyDoesNotExist(key: Key)
case fetch(entityName: String)
}
I've abstracted my coredata writes in a protocol. I'd appreciate if you let me know of your comments about the abstraction I'm trying to pull off.
Yet in the extension I run into the following error:
Cannot convert value of type 'NSFetchRequest' to
expected argument type 'NSFetchRequest<_>'
Not sure exactly how I can fix it. I've tried variations of changing my code but didn't find success...
protocol CoreDataWriteManagerProtocol {
associatedtype ManagedObject : NSManagedObject
var persistentContainer : NSPersistentContainer {get}
var idName : String {get}
func loadFromDB(storableClass : ManagedObject.Type, id: ID) throws -> CoreDataResult<ManagedObject>
func update(storableClass : ManagedObject.Type, id: ID, fields: [String : Any]) throws
func fetch(request: NSFetchRequest<ManagedObject>, from context: NSManagedObjectContext)
init(persistentContainer : NSPersistentContainer)
}
extension CoreDataWriteManagerProtocol {
private func loadFromDB(storableClass : ManagedObject.Type, id: ID) -> CoreDataResult<ManagedObject>{
let predicate = NSPredicate(format: "%# == %#", idName, id)
let fetchRequest : NSFetchRequest = storableClass.fetchRequest()
fetchRequest.predicate = predicate
// ERROR at below line!
return fetch(request: fetchRequest, from: persistentContainer.viewContext)
}
func fetch<ManagedObject: NSManagedObject>(request: NSFetchRequest<ManagedObject>, from context: NSManagedObjectContext) -> CoreDataResult<ManagedObject>{
guard let results = try? context.fetch(request) else {
return .failure(CoreDataResponseError.fetch(entityName: request.entityName ?? "Empty Entity Name")) // #TODO not sure if entityName gets passed or not.
}
if let result = results.first {
return .success(result)
}else{
return .failure(CoreDataResponseError.idDoesNotExist)
}
}
}
Additionally if I change the line:
let fetchRequest : NSFetchRequest = storableClass.fetchRequest()
to:
let fetchRequest : NSFetchRequest<storableClass> = storableClass.fetchRequest()
I get the following error:
Use of undeclared type 'storableClass'`
My intuition tells me that the compiler can't map 'parameters that are types' ie it doesn't understand that storableClass is actually a type. Instead it can only map generics parameters or actual types. Hence this doesn't work.
EDIT:
I used static approach Vadian and wrote this:
private func create(_ entityName: String, json : [String : Any]) throws -> ManagedObject {
guard let entityDescription = NSEntityDescription.entity(forEntityName: entityName, in: Self.persistentContainer.viewContext) else {
print("entityName: \(entityName) doesn't exist!")
throw CoreDataError.entityNotDeclared(name: entityName)
}
let _ = entityDescription.relationships(forDestination: NSEntityDescription.entity(forEntityName: "CountryEntity", in: Self.persistentContainer.viewContext)!)
let relationshipsByName = entityDescription.relationshipsByName
let propertiesByName = entityDescription.propertiesByName
guard let managedObj = NSEntityDescription.insertNewObject(forEntityName: entityName, into: Self.persistentContainer.viewContext) as? ManagedObject else {
throw CoreDataError.entityNotDeclared(name: entityName)
}
for (propertyName,_) in propertiesByName {
if let value = json[propertyName] {
managedObj.setValue(value, forKey: propertyName)
}
}
// set all the relationships
guard !relationshipsByName.isEmpty else {
return managedObj
}
for (relationshipName, _ ) in relationshipsByName {
if let object = json[relationshipName], let objectDict = object as? [String : Any] {
let entity = try create(relationshipName, json: objectDict)
managedObj.setValue(entity, forKey: relationshipName)
}
}
return managedObj
}
But the following piece of it is not generic as in I'm casting it with as? ManagedObject. Basically it's not Swifty as Vadian puts it:
guard let managedObj = NSEntityDescription.insertNewObject(forEntityName: entityName, into: Self.persistentContainer.viewContext) as? ManagedObject else {
throw CoreDataError.entityNotDeclared(name: entityName)
}
Is there any way around that?
My suggestion is a bit different. It uses static methods
Call loadFromDB and fetch on the NSManagedObject subclass. The benefit is that always the associated type is returned without any further type cast.
Another change is throwing errors. As the Core Data API relies widely on throwing errors my suggestion is to drop CoreDataResult<Value>. All errors are passed through. On success the object is returned, on failure an error is thrown.
I left out the id related code and the update method. You can add a static func predicate(for id : ID)
protocol CoreDataWriteManagerProtocol {
associatedtype ManagedObject : NSManagedObject = Self
static var persistentContainer : NSPersistentContainer { get }
static var entityName : String { get }
static func loadFromDB(predicate: NSPredicate?) throws -> ManagedObject
static func fetch(request: NSFetchRequest<ManagedObject>) throws -> ManagedObject
static func insertNewObject() -> ManagedObject
}
extension CoreDataWriteManagerProtocol where Self : NSManagedObject {
static var persistentContainer : NSPersistentContainer {
return (UIApplication.delegate as! AppDelegate).persistentContainer
}
static var entityName : String {
return String(describing:self)
}
static func loadFromDB(predicate: NSPredicate?) throws -> ManagedObject {
let request = NSFetchRequest<ManagedObject>(entityName: entityName)
request.predicate = predicate
return try fetch(request: request)
}
static func fetch(request: NSFetchRequest<ManagedObject>) throws -> ManagedObject {
guard let results = try? persistentContainer.viewContext.fetch(request) else {
throw CoreDataResponseError.fetch(entityName: entityName)
}
if let result = results.first {
return result
} else {
throw CoreDataResponseError.idDoesNotExist
}
}
static func insertNewObject() -> ManagedObject {
return NSEntityDescription.insertNewObject(forEntityName: entityName, into: persistentContainer.viewContext) as! ManagedObject
}
}
The issue is that NSManagedObject.fetchRequest() has a return type of NSFetchRequest<NSFetchRequestResult>, which is non-generic. You need to update the definition of your fetch function to account for this. Btw the function signatures of the default implementations in the protocol extension didn't actually match the function signatures in the protocol definition, so those also need to be updated.
You also need to change the implementation of fetch(request:,from:), since NSManagedObjectContext.fetch() returns a value of type [Any], so you need to cast that to [ManagedObject] to match the type signature of your own fetch method.
protocol CoreDataWriteManagerProtocol {
associatedtype ManagedObject : NSManagedObject
var persistentContainer : NSPersistentContainer {get}
var idName : String {get}
func loadFromDB(storableClass : ManagedObject.Type, id: ID) throws -> CoreDataResult<ManagedObject>
func update(storableClass : ManagedObject.Type, id: ID, fields: [String : Any]) throws
func fetch(request: NSFetchRequest<NSFetchRequestResult>, from: NSManagedObjectContext) -> CoreDataResult<ManagedObject>
init(persistentContainer : NSPersistentContainer)
}
extension CoreDataWriteManagerProtocol {
private func loadFromDB(storableClass : ManagedObject.Type, id: ID) -> CoreDataResult<ManagedObject>{
let predicate = NSPredicate(format: "%# == %#", idName, id)
let fetchRequest = storableClass.fetchRequest()
fetchRequest.predicate = predicate
return fetch(request: fetchRequest, from: persistentContainer.viewContext)
}
func fetch(request: NSFetchRequest<NSFetchRequestResult>, from context: NSManagedObjectContext) -> CoreDataResult<ManagedObject> {
guard let results = (try? context.fetch(request)) as? [ManagedObject] else {
return .failure(CoreDataResponseError.fetch(entityName: request.entityName ?? "Empty Entity Name")) // #TODO not sure if entityName gets passed or not.
}
if let result = results.first {
return .success(result)
}else{
return .failure(CoreDataResponseError.idDoesNotExist)
}
}
}

Swift Get all the properties in generic class

I'm trying to get all the members of a generic class T, I can get the properties based on a specific class.
But, how I can do it using Mirror ?
let mirrored_object = Mirror(reflecting: user)
for (index, attr) in mirrored_object.children.enumerated() {
if let propertyName = attr.label as String! {
print("Attr \(index): \(propertyName) = \(attr.value)")
}
}
I added this as extension
extension NSObject {
public func GetAsJson() -> [[String:Any?]] {
var result:[[String: Any?]] = [[String: Any?]]()
for item in self {
var dict: [String: Any?] = [:]
for property in Mirror(reflecting: self).children {
dict[property.label!] = property.value
}
result.append(dict)
}
return result
}
}

Hold reference to downloaded DynamoDB data

I have a class holding a DynamoDB model (I cut the # of variables for brevity, but they're all Optional Strings:
import AWSCore
import AWSDynamoDB
#objcMembers class Article: AWSDynamoDBObjectModel, AWSDynamoDBModeling {
var _articleSource: String?
class func dynamoDBTableName() -> String {
return "article"
}
class func hashKeyAttribute() -> String {
return "_articleId"
}
class func rangeKeyAttribute() -> String {
return "_articleUrl"
}
override class func jsonKeyPathsByPropertyKey() -> [AnyHashable: Any] {
return [
"_articleSource" : "articles.articleSource",
]
}
}
In my View Controller, I'm downloading data from the table and storing each article in an array like this:
let dynamoDbObjectMapper = AWSDynamoDBObjectMapper.default()
var allArticles = [AnyObject]()
func getArticles(completed: #escaping DownloadComplete) {
let scanExpression = AWSDynamoDBScanExpression()
scanExpression.limit = 50
self.dynamoDbObjectMapper.scan(Article.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
if let error = task.error as NSError? {
print("The request failed. Error: \(error)")
} else if let paginatedOutput = task.result {
for article in paginatedOutput.items as! [Article] {
self.allArticles.append(article)
}
}
return(self.allArticles)
})
completed()
}
When I try to work with the data that should be stored in allArticles the array is empty. However, the array holds articles when I break execution in the download block where articles are being appended. How can I hold reference to the downloaded data? My use of a completion block was my attempt.
Edit: allArticles is of type [AnyObject] because I'm attempting to store objects from 3 different classes total in the same array to make it easier to work with in a TableView
The array wasn't empty after all, I just didn't realize this was all async (duh...)
I just needed:
DispatchQueue.main.async {
self.tableView.reloadData()
}
in place of completed() in the getArticles() func