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
}
}
}
Related
In my swift code below the code saves an item in core data. The goal is to overwrite that item. I am getting a runtime error at
CoreDataHandler.changeName(user: fetchUser!\[indexNumber\], jessica: "jo")
Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
I don't know how to wrap in the index number. The goal is it to print judo then jo
import UIKit;import CoreData
class ViewController: UIViewController {
var fetchUser: [UserInfo]? = nil
var indexNumber : Int = 0
override func viewDidLoad() {
super.viewDidLoad()
CoreDataHandler.saveObject2( name: "judo")
getText(textNo: indexNumber)
saveTheItem()
}
#objc func saveTheItem(){
CoreDataHandler.changeName(user: fetchUser![indexNumber], jessica: "jo")
}
func getText(textNo:Int) {
// first check the array bounds
let info = helpText.shareInstance.fetchText()
if info.count > textNo {
if let imageData = info[textNo].name
{
print(imageData)
} else {
// no data
print("data is empty Textss")
}
} else {
// image number is greater than array bounds
print("you are asking out of bounds")
}
}
}
class CoreDataHandler : NSManagedObject {
class func saveObject2( name: String) -> Bool {
let context = getContext()
let entity = NSEntityDescription.entity(forEntityName: "UserInfo", in: context)
let managedObject = NSManagedObject(entity: entity!, insertInto: context)
managedObject.setValue(name, forKey: "name")
do{
try context.save()
return true
}
catch {
return false
}
}
private class func getContext() -> NSManagedObjectContext{
let appD = UIApplication.shared.delegate as! AppDelegate
return appD.persistentContainer.viewContext
}
class func changeName(user: UserInfo,jessica : String) -> Bool
{
let context = getContext()
user.name = jessica
print(jessica)
do{
try context.save()
return true
}
catch{
return false
}
}
}
class helpText: UIViewController{
private class func getContext() -> NSManagedObjectContext {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
return appDelegate.persistentContainer.viewContext
}
static let shareInstance = helpText()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
func saveName(data: String) {
let imageInstance = UserInfo(context: context)
imageInstance.name = data
do {
try context.save()
} catch {
print(error.localizedDescription)
}
}
func fetchText() -> [UserInfo] {
var fetchingImage = [UserInfo]()
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "UserInfo")
do {
fetchingImage = try context.fetch(fetchRequest) as! [UserInfo]
} catch {
print("Error while fetching the image")
}
return fetchingImage
}
}
No offense but your code is a mess.
And there is a big misunderstanding. Core Data records are unordered, there is no index. To update a record you have to fetch it by a known attribute, in your example by name, update it and save it back.
This is a simple method to do that. It searches for a record with the given name. If there is one, update the attribute with newName and save the record.
The code assumes that there is a NSManagedObject subclass UserInfo with implemented class method fetchRequest.
func changeName(_ name: String, to newName: String) {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let request : NSFetchRequest<UserInfo> = UserInfo.fetchRequest()
request.predicate = NSPredicate(format: "name == %#", name)
do {
let records = try context.fetch(request)
guard let foundRecord = records.first else { return }
foundRecord.name = newName
try context.save()
} catch {
print(error)
}
}
Regarding your confusing code:
Create CoreDataHandler as singleton (and it must not be a subclass of NSManagedObject). Move the Core Data related code from AppDelegate and the methods to read and write in this class.
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)
}
}
}
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 :-)
In Swift 2 the following code was working:
let request = NSFetchRequest(entityName: String)
but in Swift 3 it gives error:
Generic parameter "ResultType" could not be inferred
because NSFetchRequest is now a generic type. In their documents they wrote this:
let request: NSFetchRequest<Animal> = Animal.fetchRequest
so if my result class is for example Level how should I request correctly?
Because this not working:
let request: NSFetchRequest<Level> = Level.fetchRequest
let request: NSFetchRequest<NSFetchRequestResult> = Level.fetchRequest()
or
let request: NSFetchRequest<Level> = Level.fetchRequest()
depending which version you want.
You have to specify the generic type because otherwise the method call is ambiguous.
The first version is defined for NSManagedObject, the second version is generated automatically for every object using an extension, e.g:
extension Level {
#nonobjc class func fetchRequest() -> NSFetchRequest<Level> {
return NSFetchRequest<Level>(entityName: "Level");
}
#NSManaged var timeStamp: NSDate?
}
The whole point is to remove the usage of String constants.
I think i got it working by doing this:
let request:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "Level")
at least it saves and loads data from DataBase.
But it feels like it is not a proper solution, but it works for now.
The simplest structure I found that works in 3.0 is as follows:
let request = NSFetchRequest<Country>(entityName: "Country")
where the data entity Type is Country.
When trying to create a Core Data BatchDeleteRequest, however, I found that this definition does not work and it seems that you'll need to go with the form:
let request: NSFetchRequest<NSFetchRequestResult> = Country.fetchRequest()
even though the ManagedObject and FetchRequestResult formats are supposed to be equivalent.
Here are some generic CoreData methods that might answer your question:
import Foundation
import Cocoa
func addRecord<T: NSManagedObject>(_ type : T.Type) -> T
{
let entityName = T.description()
let context = app.managedObjectContext
let entity = NSEntityDescription.entity(forEntityName: entityName, in: context)
let record = T(entity: entity!, insertInto: context)
return record
}
func recordsInTable<T: NSManagedObject>(_ type : T.Type) -> Int
{
let recs = allRecords(T.self)
return recs.count
}
func allRecords<T: NSManagedObject>(_ type : T.Type, sort: NSSortDescriptor? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func query<T: NSManagedObject>(_ type : T.Type, search: NSPredicate?, sort: NSSortDescriptor? = nil, multiSort: [NSSortDescriptor]? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
if let predicate = search
{
request.predicate = predicate
}
if let sortDescriptors = multiSort
{
request.sortDescriptors = sortDescriptors
}
else if let sortDescriptor = sort
{
request.sortDescriptors = [sortDescriptor]
}
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func deleteRecord(_ object: NSManagedObject)
{
let context = app.managedObjectContext
context.delete(object)
}
func deleteRecords<T: NSManagedObject>(_ type : T.Type, search: NSPredicate? = nil)
{
let context = app.managedObjectContext
let results = query(T.self, search: search)
for record in results
{
context.delete(record)
}
}
func saveDatabase()
{
let context = app.managedObjectContext
do
{
try context.save()
}
catch
{
print("Error saving database: \(error)")
}
}
Assuming that there is a NSManagedObject setup for Contact like this:
class Contact: NSManagedObject
{
#NSManaged var contactNo: Int
#NSManaged var contactName: String
}
These methods can be used in the following way:
let name = "John Appleseed"
let newContact = addRecord(Contact.self)
newContact.contactNo = 1
newContact.contactName = name
let contacts = query(Contact.self, search: NSPredicate(format: "contactName == %#", name))
for contact in contacts
{
print ("Contact name = \(contact.contactName), no = \(contact.contactNo)")
}
deleteRecords(Contact.self, search: NSPredicate(format: "contactName == %#", name))
recs = recordsInTable(Contact.self)
print ("Contacts table has \(recs) records")
saveDatabase()
This is the simplest way to migrate to Swift 3.0, just add <Country>
(tested and worked)
let request = NSFetchRequest<Country>(entityName: "Country")
Swift 3.0 This should work.
let request: NSFetchRequest<NSFetchRequestResult> = NSManagedObject.fetchRequest()
request.entity = entityDescription(context)
request.predicate = predicate
I also had "ResultType" could not be inferred errors. They cleared once I rebuilt the data model setting each entity's Codegen to "Class Definition". I did a brief writeup with step by step instructions here:
Looking for a clear tutorial on the revised NSPersistentContainer in Xcode 8 with Swift 3
By "rebuilt" I mean that I created a new model file with new entries and attributes. A little tedious, but it worked!
What worked best for me so far was:
let request = Level.fetchRequest() as! NSFetchRequest<Level>
I had the same issue and I solved it with the following steps:
Select your xcdatamodeld file and go to the Data Model Inspector
Select your first Entity and go to Section class
Make sure that Codegen "Class Definition" is selected.
Remove all your generated Entity files. You don't need them anymore.
After doing that I had to remove/rewrite all occurences of fetchRequest as XCode seem to somehow mix up with the codegenerated version.
HTH
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
func loadItemsCategory() {
let request: NSFetchRequest<Category> = Category.fetchRequest()
do {
categoryArray = try context.fetch(request)
} catch {
print(error)
}
tableView.reloadData()
}
In Swift 2 the following code was working:
let request = NSFetchRequest(entityName: String)
but in Swift 3 it gives error:
Generic parameter "ResultType" could not be inferred
because NSFetchRequest is now a generic type. In their documents they wrote this:
let request: NSFetchRequest<Animal> = Animal.fetchRequest
so if my result class is for example Level how should I request correctly?
Because this not working:
let request: NSFetchRequest<Level> = Level.fetchRequest
let request: NSFetchRequest<NSFetchRequestResult> = Level.fetchRequest()
or
let request: NSFetchRequest<Level> = Level.fetchRequest()
depending which version you want.
You have to specify the generic type because otherwise the method call is ambiguous.
The first version is defined for NSManagedObject, the second version is generated automatically for every object using an extension, e.g:
extension Level {
#nonobjc class func fetchRequest() -> NSFetchRequest<Level> {
return NSFetchRequest<Level>(entityName: "Level");
}
#NSManaged var timeStamp: NSDate?
}
The whole point is to remove the usage of String constants.
I think i got it working by doing this:
let request:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "Level")
at least it saves and loads data from DataBase.
But it feels like it is not a proper solution, but it works for now.
The simplest structure I found that works in 3.0 is as follows:
let request = NSFetchRequest<Country>(entityName: "Country")
where the data entity Type is Country.
When trying to create a Core Data BatchDeleteRequest, however, I found that this definition does not work and it seems that you'll need to go with the form:
let request: NSFetchRequest<NSFetchRequestResult> = Country.fetchRequest()
even though the ManagedObject and FetchRequestResult formats are supposed to be equivalent.
Here are some generic CoreData methods that might answer your question:
import Foundation
import Cocoa
func addRecord<T: NSManagedObject>(_ type : T.Type) -> T
{
let entityName = T.description()
let context = app.managedObjectContext
let entity = NSEntityDescription.entity(forEntityName: entityName, in: context)
let record = T(entity: entity!, insertInto: context)
return record
}
func recordsInTable<T: NSManagedObject>(_ type : T.Type) -> Int
{
let recs = allRecords(T.self)
return recs.count
}
func allRecords<T: NSManagedObject>(_ type : T.Type, sort: NSSortDescriptor? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func query<T: NSManagedObject>(_ type : T.Type, search: NSPredicate?, sort: NSSortDescriptor? = nil, multiSort: [NSSortDescriptor]? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
if let predicate = search
{
request.predicate = predicate
}
if let sortDescriptors = multiSort
{
request.sortDescriptors = sortDescriptors
}
else if let sortDescriptor = sort
{
request.sortDescriptors = [sortDescriptor]
}
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func deleteRecord(_ object: NSManagedObject)
{
let context = app.managedObjectContext
context.delete(object)
}
func deleteRecords<T: NSManagedObject>(_ type : T.Type, search: NSPredicate? = nil)
{
let context = app.managedObjectContext
let results = query(T.self, search: search)
for record in results
{
context.delete(record)
}
}
func saveDatabase()
{
let context = app.managedObjectContext
do
{
try context.save()
}
catch
{
print("Error saving database: \(error)")
}
}
Assuming that there is a NSManagedObject setup for Contact like this:
class Contact: NSManagedObject
{
#NSManaged var contactNo: Int
#NSManaged var contactName: String
}
These methods can be used in the following way:
let name = "John Appleseed"
let newContact = addRecord(Contact.self)
newContact.contactNo = 1
newContact.contactName = name
let contacts = query(Contact.self, search: NSPredicate(format: "contactName == %#", name))
for contact in contacts
{
print ("Contact name = \(contact.contactName), no = \(contact.contactNo)")
}
deleteRecords(Contact.self, search: NSPredicate(format: "contactName == %#", name))
recs = recordsInTable(Contact.self)
print ("Contacts table has \(recs) records")
saveDatabase()
This is the simplest way to migrate to Swift 3.0, just add <Country>
(tested and worked)
let request = NSFetchRequest<Country>(entityName: "Country")
Swift 3.0 This should work.
let request: NSFetchRequest<NSFetchRequestResult> = NSManagedObject.fetchRequest()
request.entity = entityDescription(context)
request.predicate = predicate
I also had "ResultType" could not be inferred errors. They cleared once I rebuilt the data model setting each entity's Codegen to "Class Definition". I did a brief writeup with step by step instructions here:
Looking for a clear tutorial on the revised NSPersistentContainer in Xcode 8 with Swift 3
By "rebuilt" I mean that I created a new model file with new entries and attributes. A little tedious, but it worked!
What worked best for me so far was:
let request = Level.fetchRequest() as! NSFetchRequest<Level>
I had the same issue and I solved it with the following steps:
Select your xcdatamodeld file and go to the Data Model Inspector
Select your first Entity and go to Section class
Make sure that Codegen "Class Definition" is selected.
Remove all your generated Entity files. You don't need them anymore.
After doing that I had to remove/rewrite all occurences of fetchRequest as XCode seem to somehow mix up with the codegenerated version.
HTH
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
func loadItemsCategory() {
let request: NSFetchRequest<Category> = Category.fetchRequest()
do {
categoryArray = try context.fetch(request)
} catch {
print(error)
}
tableView.reloadData()
}