批量删除NSManagedObject时，Core Data为何触发对象故障？

Hey Andrew, let's break down why your batch deletion is still triggering object faults even with includesPropertyValues = false set, and fix it with a more robust approach that avoids unnecessary faulting.

Why Faults Are Still Happening #

Even when you set includesPropertyValues = false, the objects you fetch are still faulted NSManagedObject instances. When you call context.delete(object), Core Data may need to resolve the fault to verify the object's state (like confirming it's still attached to the context or hasn't been deleted elsewhere). Plus, if your pre-delete logs accidentally access any property of the object (even just printing the object itself), that will force Core Data to load the object's data and trigger a fault.

Optimized Batch Deletion Workflow (No Fault Triggers) #

Let's adjust your approach to avoid loading full object instances entirely until the exact moment we need to delete them:

1. Fetch Only Object IDs Instead of Full Objects #

This skips loading any object data entirely—we just grab the unique identifiers we need to target for deletion:

func fetchEntityObjectIDs(batchSize: Int) throws -> [NSManagedObjectID] {
    let fetchRequest: NSFetchRequest<NSFetchRequestResult> = YourTargetEntity.fetchRequest()
    // Tell Core Data to return only object IDs, not full objects
    fetchRequest.resultType = .managedObjectIDResultType
    fetchRequest.fetchBatchSize = batchSize
    
    return try persistentContainer.viewContext.fetch(fetchRequest) as! [NSManagedObjectID]
}

2. Batch Delete Using Object IDs #

With the list of IDs, we process them in chunks, fetch only the necessary object to delete, then reset the context to free up memory immediately:

func batchDeleteWithObjectIDs(_ objectIDs: [NSManagedObjectID], batchSize: Int) throws {
    let context = persistentContainer.viewContext
    // Split IDs into manageable batches
    let idBatches = objectIDs.chunked(into: batchSize)
    
    for batch in idBatches {
        context.performAndWait {
            do {
                for objectID in batch {
                    // Fetch the object only if it still exists in the context
                    guard let targetObject = try? context.existingObject(with: objectID) else {
                        // Skip if the object was already deleted elsewhere
                        continue
                    }
                    context.delete(targetObject)
                }
                // Save the batch deletion
                try context.save()
                // Reset context to clear all cached objects and free memory
                context.reset()
            } catch {
                print("Batch deletion failed: \(error.localizedDescription)")
                context.rollback()
            }
        }
    }
}

// Helper extension to split arrays into batches
extension Array {
    func chunked(into size: Int) -> [[Element]] {
        return stride(from: 0, to: count, by: size).map {
            Array(self[$0..<Swift.min($0 + size, count)])
        }
    }
}

3. Critical Rules to Avoid Faults #

• Never access object properties before deletion: Even printing the object's description or checking a property will force Core Data to resolve the fault. Stick to only using the object ID until you're ready to call delete().
• Reset the context immediately after saving: This clears all in-memory managed objects right after each batch, preventing memory bloat and unnecessary fault resolution for past batches.
• Use managedObjectIDResultType: This is far more reliable than includesPropertyValues = false for avoiding object data loading, since we never retrieve full object instances until absolutely necessary.

内容的提问来源于stack exchange，提问作者Andrew Bennet