reload table with async search result - swift

Question

I large amount of data in my app with search functionality. I am using SQLite and Core Data to search and Fetch data.
Here is my search function,
func fetchSearchResultsWith(_ searchText : String?){
DispatchQueue.global(qos: .background).async {
var resArr : [Int64] = []
let stmt = "SELECT rowid FROM htmlText_fts WHERE htmlText MATCH '\(searchText!)*'"
do {
let res = try self.db.run(stmt)
for row in res {
resArr.append(row[0] as! Int64)
}
} catch {
print(error.localizedDescription)
}
let request : NSFetchRequest<Monos> = Monos.fetchRequest()
request.fetchLimit = 200
let predicate = NSPredicate(format: "id in %#", resArr)
request.predicate = predicate
var arr : [Items]? = []
do {
arr = try context.fetch(request)
} catch {
print(error.localizedDescription)
}
DispatchQueue.main.async(execute: {
self.monosSearchResult = arr
self.tableView.reloadData()
})
}
}
I am using DispatchQueue.global.async to avoid freezing UI, but then its returning async array and my table view ends up reloading with wrong result. If I use DispatchQueue.global.sync it works fine, but then my UI freezes when I type in to searchBar. I am not sure what I can do get right result. Any help will be appreciated!
Please let me know if you need any further information.

Answer 1

Since you have a 2 step search mechanism , a new search may be initiated before the other ones end , so to lightWeight this operation , store the last value of the textfield inside a var
lastSear = textfield.text
fetchSearchResultsWith(lastSear)
then do this inside the search function in 3 places
Before search the DB & after & before setting the array and reloading the table
if searchText != lastSear { return }

Answer 2

You have not included your table data source methods which populate the table, but I assume you are using values from self.monosSearchResult. If not, then your fetch code is populating the wrong values, and that may be part of your problem.
Additionally, your fetch request needs to be running on the appropriate thread for your NSManagedObjectContext, not necessarily (probably not) the global background queue. NSManagedObjectContext provides the perform and performAndWait methods for you to use their queues properly.
func fetchSearchResultsWith(_ searchText : String?){
// context: NSManagedObjectContext, presumably defined in this scope already
// since you use it below for the fetch.
// CHANGE THIS
// DispatchQueue.global(qos: .background).async {
// TO THIS
context.perform { // run block asynchronously on the context queue
var resArr : [Int64] = []
let stmt = "SELECT rowid FROM htmlText_fts WHERE htmlText MATCH '\(searchText!)*'"
do {
let res = try self.db.run(stmt)
for row in res {
resArr.append(row[0] as! Int64)
}
} catch {
print(error.localizedDescription)
}
let request : NSFetchRequest<Monos> = Monos.fetchRequest()
request.fetchLimit = 200
let predicate = NSPredicate(format: "id in %#", resArr)
request.predicate = predicate
var arr : [Items]? = []
do {
arr = try context.fetch(request)
} catch {
print(error.localizedDescription)
}
DispatchQueue.main.async(execute: {
self.monosSearchResult = arr
self.tableView.reloadData()
})
}
}