Update all value in one attribute Core Data - swift

Question

I know how to fetch all value from one attribute in Core Data using an array. I just need to press a button and -1 all the value and save it back to the Core Data.
How can I update all the value once in swift?
Thanks.

Answer 1

For swift 3
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Params")
do{
if let fetchResults = try managedContext.fetch(request) as? [NSManagedObject] {
if fetchResults.count != 0 {
for index in 0...fetchResults.count-1 {
let managedObject = fetchResults[index]
managedObject.setValue("-1", forKey: "value")
}
try managedContext.save()
}
}
} catch let error as NSError {
print("Could not fetch \(error), \(error.userInfo)")
}

Answer 2

Try following example it might be helpful.Replace you entity name.
var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
var context: NSManagedObjectContext = appDel.managedObjectContext!
var request = NSFetchRequest(entityName: "Params")
var params = NSEntityDescription.insertNewObjectForEntityForName("Params", inManagedObjectContext: context) as! NSManagedObject
if let fetchResults = appDel.managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [NSManagedObject] {
if fetchResults.count != 0{
for (var v = 0 ; v < fetchResults.count ; v++) {
var managedObject = fetchResults[v]
println(fetchResults)
managedObject.setValue("-1", forKey: "value")
context.save(nil)
}
}
}

Answer 3

While the question is quiet old, I am writing it for those who wish to do this task in a more optimized manner. According to the documentation,
Batch updates run faster than processing the Core Data entities yourself in code because they operate in the persistent store itself, at the SQL level.
Hence using NSBatchUpdateRequest is the best way to achieve the result. Here's a swift code that could do the job in the given scenario with using an extension to help simplify the code while also taking into account the fact that changes made in batch update are not reflected in the objects currently in memory.
extension NSManagedObjectContext {
/// Executes the given `NSBatchUpdateRequest` and directly merges the changes to bring the given managed object context up to date.
///
/// - Parameter batchUpdateRequest: The `NSBatchUpdateRequest` to execute.
/// - Throws: An error if anything went wrong executing the batch deletion.
public func executeAndMergeChanges(using batchUpdateRequest: NSBatchUpdateRequest) throws {
batchUpdateRequest.resultType = .updatedObjectIDsResultType
let result = try execute(batchUpdateRequest) as? NSBatchUpdateResult
let changes: [AnyHashable: Any] = [NSUpdatedObjectsKey: result?.result as? [NSManagedObjectID] ?? []]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [self])
}
}
class MyCoreDataClass {
...
func updateAllParams() {
let request = NSBatchUpdateRequest(entityName: "Params")
request.propertiesToUpdate = ["value" : NSExpression(forConstantValue: -1)]
do {
try managedObjectContext.executeAndMergeChanges(using: request)
} catch {
print(error)
}
}
}
P.S: You need to be aware that validation rules enforced in data model are not considered while executing a batch update. According to the documentation,
When you use batch updates any validation rules that are a part of the data model are not enforced when the batch update is executed. Therefore, ensure that any changes caused by the batch update will continue to pass the validation rules.