Core Data - Fetch all entities using the same field - ios

Question

in my ios swift application I have a database using Core Data.
It has many entities, all entities have an integer field called syncStatus. it can be 0, 1, or 2.
On startup, I want to loop through ALL the entities that have syncStatus = 1 and change it to 0
Is there a way to do it without fetching each type alone and changing it?
So what I want is:
fetch ALL entities with syncStatus = 1
Loop through them and set syncStatus = 0
Currently I'm doing them one by one:
fetch UserEntities with syncStatus = 1
Loop through them and set syncStatus = 0
fetch countryEntities with syncStatus = 1
Loop through them and set syncStatus = 0
Do the same for every entity one by one
code:
let allUsers = context?.fetch(FetchRequest<UserEntity>().filtered(with: "syncStatus", equalTo: "1"))
let allCountries = context?.fetch(FetchRequest<CountryEntity>().filtered(with: "syncStatus", equalTo: "1"))
.
.
.
I'm just trying to find a generic approach, in case later we add another entity/table we don't have to come back to this code and add it here also.

Answer 1

First of all, fetching all entries and filter them is much more expensive than applying a predicate.
I recommend to use a protocol extension with static methods. The benefit is that you can call the methods directly on the type
protocol SyncStatusResettable
{
associatedtype Entity: NSManagedObject = Self
var syncStatus : String {get set}
static var entityName : String { get }
static func resetSyncStatus(in context: NSManagedObjectContext) throws
}
extension SyncStatusResettable where Entity == Self
{
static var entityName : String {
return NSStringFromClass(self).components(separatedBy: ".").last!
}
static func resetSyncStatus(in context: NSManagedObjectContext) throws
{
let request = NSFetchRequest<Entity>(entityName: entityName)
request.predicate = NSPredicate(format: "syncStatus == 1")
let items = try context.fetch(request)
for var item in items { item.syncStatus = "0" }
if context.hasChanges { try context.save() }
}
}
To use it, adopt SyncStatusResettable for all NSManagedObject subclasses and call
do {
try UserEntity.resetSyncStatus(in: managedObjectContext)
try CountryEntity.resetSyncStatus(in: managedObjectContext)
} catch { print(error) }
managedObjectContext is the current NSManagedObjectContext instance

Answer 2

NSManagedObjectModel allows you to enumerate through the entities it contains, and NSEntityDescription can give you properties for each entity. Once you have a reference to the model:
let entitiesWithSync = model.entities.filter {
$0.properties.contains(where: { $0.name == "syncStatus" })
}
Will give you all of the relevant entities. You can then use this list of entities to drive your updates - note that using NSBatchUpdateRequest is faster if you're doing this on startup. You can create batch update requests using the entity descriptions obtained in the loop above.

Answer 3

In the past I have looped through all the entitiesByName from the object model:
lazy var managedObjectModel: NSManagedObjectModel = {
let modelUrl = NSBundle.mainBundle().URLForResource("SomeProject", withExtension: "momd")!
return NSManagedObjectModel(contentsOf: modelUrl)
}
func updateAllData() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
context.performAndWait {
let allEntities = self.managedObjectModel.entitiesByName
for (entity, items) in allEntities {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
...
}
}
}