Query for data to add data to prepareForSegue function - swift

Question

I am attempting to query for data from a Parse table to add it to a prepareForSegue function. But once I go into the newViewController the label is blank. Here's my line of code.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if(segue.identifier == "marathonDetail"){
var upcoming: marathonDetailViewController = segue.destinationViewController as! marathonDetailViewController
let indexPath = self.marathonsTableView.indexPathForSelectedRow!
let currentCell = marathonsTableView.cellForRowAtIndexPath(indexPath) as! marathonTableViewCell
let marathonEvents = currentCell.marathonName.text
upcoming.nameMarathon = marathonEvents
self.marathonsTableView.deselectRowAtIndexPath(indexPath, animated: true)
var query = PFQuery(className: "marathons")
query.whereKey("marathonName", equalTo: marathonEvents!)
query.findObjectsInBackgroundWithBlock{
(marathonPickeds: [PFObject]?, error: NSError?) -> Void in
if (error == nil){
if let marathonPicked = marathonPickeds as? [PFObject]?{
for marathonPicked in marathonPickeds!{
var selectedDescription = marathonPicked.description
upcoming.marathonDescription = selectedDescription
print(selectedDescription)
}
}
}else {
print(error)
}
}
}
}
The marathonsEvents= currentCell.marathonName.text works well but the marathonDescription is blank.
Any advice? I am using Parse as my backend XCODE 7, and swift

Answer 1

You're performing a network call on a background thread so by the time its finished you've already completed the segue. What you probably want to do is:
Pull that query logic out into a separate class, get it out of your view controllers.
In this instance perform the request in the view controller that is being pushed to. You can start it in viewWillAppear and refresh your view when its finished. It looks like it has all the information it needs to perform the request using just the marathonEvents.