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+--- Thread: How to apply the type to a NSFetchRequest instance? (/Thread-How-to-apply-the-type-to-a-NSFetchRequest-instance)
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How to apply the type to a NSFetchRequest instance? - Sirencaustics397 - 07-18-2023
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
RE: How to apply the type to a NSFetchRequest instance? - Mrgeorgiannernodgebdca - 07-18-2023
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()
}
RE: How to apply the type to a NSFetchRequest instance? - stagnancy549622 - 07-18-2023
Swift 3.0 This should work.
let request: NSFetchRequest<NSFetchRequestResult> = NSManagedObject.fetchRequest()
request.entity = entityDescription(context)
request.predicate = predicate
RE: How to apply the type to a NSFetchRequest instance? - Proparus995 - 07-18-2023
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
RE: How to apply the type to a NSFetchRequest instance? - secondar749552 - 07-18-2023
This is the simplest way to migrate to Swift 3.0, just add `<Country>`
(tested and worked)
let request = NSFetchRequest<Country>(entityName: "Country")
RE: How to apply the type to a NSFetchRequest instance? - oralwusvhrzzr - 07-18-2023
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()
RE: How to apply the type to a NSFetchRequest instance? - parolee166 - 07-18-2023
What worked best for me so far was:
let request = Level.fetchRequest() as! NSFetchRequest<Level>
RE: How to apply the type to a NSFetchRequest instance? - inez14 - 07-18-2023
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:
[To see links please register here]
By "rebuilt" I mean that I created a new model file with new entries and attributes. A little tedious, but it worked!
RE: How to apply the type to a NSFetchRequest instance? - beaudette615 - 07-18-2023
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.
RE: How to apply the type to a NSFetchRequest instance? - Sirzipper680 - 07-18-2023
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.