Sort Parse Query based on difference with Float

Question

I want to sort the results of my Parse Query based on the scalar distance from the field temperature to my variable referenceTemp

I tried the following, which of course does not work, but it illustrates my intention

var referenceTemp = 47.89
var query = PFQuery(className: "Temperatures")
query.orderByAscending("abs(temperature - referenceTemp)")

How can I do it? Thanks!!

Answer 1

You can't do this on the database level... but you can do it with two queries:

var referenceTemp = 47.89
var query = PFQuery(className: "Temperatures")
query.greaterThan(referenceTemp);
query.orderByAscending();
query.findObjectsInBackgroundWithBlock {
  (objects: [AnyObject]?, error: NSError?) -> Void in

  if error == nil {
    // The find succeeded.
    println("Successfully retrieved \(objects!.count) scores.")
    // Do something with the found objects
    if let objects = objects as? [PFObject] {
      for object in objects {
        //Get the scalar distance for each, store
      }
    }
  } else {
    // Log details of the failure
    println("Error: \(error!) \(error!.userInfo!)")
  }
}

query.lessThan(referenceTemp);
query.orderByDescending();
query.findObjectsInBackgroundWithBlock...

Once you have both the closest above and below, and their scalar distances, you could use a hash or an NSDictionary with keys of scalar distance and values of the objects. Order as needed and you're there in only 2 queries.