2015-02-05 Swift example of a batch update in Core Data

Here's a Swift example of doing a batch update in Core Data:

	let updateRequest = NSBatchUpdateRequest("some_entity_name")
	let predicateIsRead = NSPredicate(format: "isRead = %@", NSNumber(bool: true))
	updateRequest.predicate = predicateIsRead
	updateRequest.propertiesToUpdate = [
		ContentItemAttributes.isRead.rawValue: NSNumber(bool: false)
	updateRequest.resultType = NSBatchUpdateRequestResultType.UpdatedObjectsCountResultType
	var error: NSError?
	let updateResult = objectContext.executeRequest(updateRequest, error: &error) as NSBatchUpdateResult?
	if let result = updateResult {
		let count = result.result as Int
		println("Updated \(count) rows")
	} else {
		println("Error during batch update: \(error?.localizedDescription)")

Note that you'll need to update the objects in memory. The above code just prints the row count. If you have stuff displayed in the user interface, use this answer on Stack Overflow to adjust the above code.