Core Data: Quickest Way to Delete All Instances of an Entity

Core Data: Quickest way to delete all instances of an entity

iOS 9 and later:

iOS 9 added a new class called NSBatchDeleteRequest that allows you to easily delete objects matching a predicate without having to load them all in to memory. Here's how you'd use it:

Swift 5

let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "Car")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)

do {
try myPersistentStoreCoordinator.execute(deleteRequest, with: myContext)
} catch let error as NSError {
// TODO: handle the error


NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Car"];
NSBatchDeleteRequest *delete = [[NSBatchDeleteRequest alloc] initWithFetchRequest:request];

NSError *deleteError = nil;
[myPersistentStoreCoordinator executeRequest:delete withContext:myContext error:&deleteError];

More information about batch deletions can be found in the "What's New in Core Data" session from WWDC 2015 (starting at ~14:10).

iOS 8 and earlier:

Fetch 'em all and delete 'em all:

NSFetchRequest *allCars = [[NSFetchRequest alloc] init];
[allCars setEntity:[NSEntityDescription entityForName:@"Car" inManagedObjectContext:myContext]];
[allCars setIncludesPropertyValues:NO]; //only fetch the managedObjectID

NSError *error = nil;
NSArray *cars = [myContext executeFetchRequest:allCars error:&error];
[allCars release];
//error handling goes here
for (NSManagedObject *car in cars) {
[myContext deleteObject:car];
NSError *saveError = nil;
[myContext save:&saveError];
//more error handling here

Clear all entities of core data DB except one entity

You can batch delete entities with a NSBatchDeleteRequest, the code assumes managedObjectContext as the current managed object context:

let entityNamesToDelete = ["Foo", "Bar", "Baz"]
let persistentStoreCoordinator = managedObjectContext.persistentStoreCoordinator!

do {
for entityName in entityNamesToDelete {
let request = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: request)

try persistentStoreCoordinator.execute(deleteRequest, with: managedObjectContext)


} catch { print(error) }

Core data delete all relationship entity

Using the example you looked at above linked as "this one".

If you use a predicate that filters the Employees by checking the relationship to Department is nil, that'd return just the data items you want. Then I suggest you could delete all of them.

iOS: Delete ALL Core Data Swift

I have got it working using the following method:

@IBAction func btnDelTask_Click(sender: UIButton){

let appDel: foodforteethAppDelegate = UIApplication.sharedApplication().delegate as foodforteethAppDelegate
let context: NSManagedObjectContext = appDel.managedObjectContext
let request = NSFetchRequest(entityName: "Food")

myList = context.executeFetchRequest(request, error: nil)

if let tv = tblTasks {

var bas: NSManagedObject!

for bas: AnyObject in myList
context.deleteObject(bas as NSManagedObject)

myList.removeAll(keepCapacity: false)


However, I am unsure whether this is the best way to go about doing it. I'm also receiving a 'constant 'bas' inferred to have anyobject' error - so if there are any solutions for that then it would be great


Fixed by changing to bas: AnyObject

How to delete all data from core data when persistentContainer is not in App delegate method in swift

One of the solutions can be to use NSBatchDeleteRequest for all entities in the persistentContainer. You can add these methods to your CoreDataStack:

func deleteAllEntities() {
let entities = persistentContainer.managedObjectModel.entities
for entity in entities {

func delete(entityName: String) {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try persistentContainer.viewContext.execute(deleteRequest)
} catch let error as NSError {

The whole code can be found here

Most efficient way to delete all core objects in objective c

Deleting objects is very fast! I realized my program was slow due to me adding images to the core data.

Delete all data in each of entity in core data swift3

You can get all the entities types in the context (in your case User, Store, Point, etc) from context.persistentStoreCoordinator.managedObjectModel.entities Next, for each entity, you can either make a fetch request to fetch all the enities and then delete each one. This will also update all FetchedResultsController that are monitoring the context. If you don't need that the faster way to do that is to use a NSBatchDeleteRequest for each entity. Don't forget to save the changes to the context at the end.

Core Data: delete all objects of an entity type, ie clear a table

Dave DeLong is an expert at, well, just about everything, and so I feel like I'm telling Jesus how to walk on water. Granted, his post is from 2009, which was a LONG time ago.

However, the approach in the link posted by Bot is not necessarily the best way to handle large deletes.

Basically, that post suggests to fetch the object IDs, and then iterate through them, calling delete on each object.

The problem is that when you delete a single object, it has to go handle all the associated relationships as well, which could cause further fetching.

So, if you must do large scale deletes like this, I suggest adjusting your overall database so that you can isolate tables in specific core data stores. That way you can just delete the entire store, and possibly reconstruct the small bits that you want to remain. That will probably be the fastest approach.

However, if you want to delete the objects themselves, you should follow this pattern...

Do your deletes in batches, inside an autorelease pool, and be sure to pre-fetch any cascaded relationships. All these, together, will minimize the number of times you have to actually go to the database, and will, thus, decrease the amount of time it takes to perform your delete.

In the suggested approach, which comes down to...

  1. Fetch ObjectIds of all objects to be deleted
  2. Iterate through the list, and delete each object

If you have cascade relationships, you you will encounter a lot of extra trips to the database, and IO is really slow. You want to minimize the number of times you have to visit the database.

While it may initially sound counterintuitive, you want to fetch more data than you think you want to delete. The reason is that all that data can be fetched from the database in a few IO operations.

So, on your fetch request, you want to set...

[fetchRequest setRelationshipKeyPathsForPrefetching:@[@"relationship1", @"relationship2", .... , @"relationship3"]];

where those relationships represent all the relationships that may have a cascade delete rule.

Now, when your fetch is complete, you have all the objects that are going to be deleted, plus the objects that will be deleted as a result of those objects being deleted.

If you have a complex hierarchy, you want to prefetch as much as possible ahead of time. Otherwise, when you delete an object, Core Data is going to have to go fetch each relationship individually for each object so that it can managed the cascade delete.

This will waste a TON of time, because you will do many more IO operations as a result.

Now, after your fetch has completed, then you loop through the objects, and delete them. For large deletes you can see an order of magnitude speed up.

In addition, if you have a lot of objects, break it up into multiple batches, and do it inside an auto release pool.

Finally, do this in a separate background thread, so your UI does not pend. You can use a separate MOC, connected to a persistent store coordinator, and have the main MOC handle DidSave notifications to remove the objects from its context.

WHile this looks like code, treat it as pseudo-code...

NSManagedObjectContext *deleteContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateConcurrencyType];
// Get a new PSC for the same store
deleteContext.persistentStoreCoordinator = getInstanceOfPersistentStoreCoordinator();

// Each call to performBlock executes in its own autoreleasepool, so we don't
// need to explicitly use one if each chunk is done in a separate performBlock
__block void (^block)(void) = ^{
NSFetchRequest *fetchRequest = //
// Only fetch the number of objects to delete this iteration
fetchRequest.fetchLimit = NUM_ENTITIES_TO_DELETE_AT_ONCE;
// Prefetch all the relationships
fetchRequest.relationshipKeyPathsForPrefetching = prefetchRelationships;
// Don't need all the properties
fetchRequest.includesPropertyValues = NO;
NSArray *results = [deleteContext executeFetchRequest:fetchRequest error:&error];
if (results.count == 0) {
// Didn't get any objects for this fetch
if (nil == results) {
// Handle error
for (MyEntity *entity in results) {
[deleteContext deleteObject:entity];
[deleteContext save:&error];
[deleteContext reset];

// Keep deleting objects until they are all gone
[deleteContext performBlock:block];

[deleteContext preformBlock:block];

Of course, you need to do appropriate error handling, but that's the basic idea.

Fetch in batches if you have so much data to delete that it will cripple memory.
Don't fetch all the properties.
Prefetch relationships to minimize IO operations.
Use autoreleasepool to keep memory from growing.
Prune the context.
Perform the task on a background thread.

If you have a really complex graph, make sure you prefetch all the cascaded relationships for all entities in your entire object graph.

Note, your main context will have to handle DidSave notifications to keep its context in step with the deletions.


Thanks. Lots of good points. All well explained except, why create the
separate MOC? Any thoughts on not deleting the entire database, but
using sqlite to delete all rows from a particular table? – David

You use a separate MOC so the UI is not blocked while the long delete operation is happening. Note, that when the actual commit to the database happens, only one thread can be accessing the database, so any other access (like fetching) will block behind any updates. This is another reason to break the large delete operation into chunks. Small pieces of work will provide some chance for other MOC(s) to access the store without having to wait for the whole operation to complete.

If this causes problems, you can also implement priority queues (via dispatch_set_target_queue), but that is beyond the scope of this question.

As for using sqlite commands on the Core Data database, Apple has repeatedly said this is a bad idea, and you should not run direct SQL commands on a Core Data database file.

Finally, let me note this. In my experience, I have found that when I have a serious performance problem, it is usually a result of either poor design or improper implementation. Revisit your problem, and see if you can redesign your system somewhat to better accommodate this use case.

If you must send down all the data, perhaps query the database in a background thread and filter the new data so you break your data into three sets: objects that need modification, objects that need deletion, and objects that need to be inserted.

This way, you are only changing the database where it needs to be changed.

If the data is almost brand new every time, consider restructuring your database where these entities have their own database (I assume your database already contains multiple entities). That way you can just delete the file, and start over with a fresh database. That's fast. Now, reinserting several thousand objects is not going to be fast.

You have to manage any relationships manually, across stores. It's not difficult, but it's not automatic like relationships within the same store.

If I did this, I would first create the new database, then tear down the existing one, replace it with the new one, and then delete the old one.

If you are only manipulating your database via this batch mechanism, and you do not need object graph management, then maybe you want to consider using sqlite instead of Core Data.

Deleting all data in a Core Data entity in Swift 3

You're thinking of NSBatchDeleteRequest, which was added in iOS 9. Create one like this:

let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Employee")
let request = NSBatchDeleteRequest(fetchRequest: fetch)

You can also add a predicate if you only wanted to delete instances that match the predicate. To run the request:

let result = try managedObjectContext.executeRequest(request)

Note that batch requests don't update any of your current app state. If you have managed objects in memory that would be affected by the delete, you need to stop using them immediately.

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