How to convert NSManagedObject Array into String Array - Swift 3 - ios

Question

I want to convert NSManagedObject Array into String Array for Search purposes. (I don't want to use predicates)
The search would be performed on an attribute "Notes" of an entity "Documents"
var documents: [NSManagedObject] = [] // data is saved in this after fetch request !
var filtered = [String]()
var dataa = [String]()
func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
//the line below is not working
// dataa = [String(describing:documents)]
filtered = dataa.filter({ (text) -> Bool in
let tmp: NSString = text as NSString
// let range = tmp.rangeOfString(searchText, options: NSString.CompareOptions.CaseInsensitiveSearch)
let range = tmp.range(of: searchText, options: NSString.CompareOptions.caseInsensitive)
return range.location != NSNotFound
})
if(filtered.count == 0){
searchActive = true;
} else {
searchActive = true;
}
self.tableView.reloadData()
}
fetched data is stored into documents (NSManagedObject) through this function & it is called on viewDidLoad()
func fetchDocuments() {
let context = getContext()
let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Documents")
//PLEASE TELL ME SOME CODE TO SAVE ALL FETCHED NOTES IN "dataa" SO THAT I CAN PERFORM FILTERING.
// It would be done like obtaining value from the nsmanagedobject via (abc.value(forKeyPath: "note") as? String)!
do {
documents = try context.fetch(fetchRequest)
self.tableView.reloadData()
} catch let error as NSError {
let errorDialog = UIAlertController(title: "Error!", message: "Failed to save! \(error): \(error.userInfo)", preferredStyle: .alert)
errorDialog.addAction(UIAlertAction(title: "Cancel", style: .cancel))
present(errorDialog, animated: true)
}
}