Backwards-compatible batch deletion

batchdeletion.swift

extension NSPersistentStoreCoordinator
{
    func batchDelete(fetchRequest: NSFetchRequest) throws
    {
        // create a worker
        let context = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
        context.persistentStoreCoordinator = self
        
        var retError: NSError!
        
        context.performBlockAndWait
        {
            do
            {
                if #available(iOS 9.0, *)
                {
                    let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
                    
                    try self.executeRequest(deleteRequest, withContext: context)
                }
                else // Fallback on earlier versions
                {
                    // make copy of request with some modifications
                    let deleteRequest = NSFetchRequest(entityName: fetchRequest.entityName!)
                    deleteRequest.predicate = fetchRequest.predicate
                    deleteRequest.includesPropertyValues = false
                    
                    // fetch all
                    let result = try context.executeFetchRequest(deleteRequest) as! [NSManagedObject]
                    
                    // delete
                    for object in result
                    {
                        context.deleteObject(object)
                    }
                    
                    // save context
                    try context.save()
                }
            }
            catch let error as NSError
            {
                retError = error
            }
        }
        
        if retError != nil
        {
            throw retError
        }
    }
}