Random row in Parse - ios

Question

I am creating an app that involves questions and facts and I need them to be selected at random. There is going to be a ton of different ones and I do not want to have to type in the ObjectId for each one of them. Is there a way to get the ObjectId of a random row so I don't have to write in the object Id for each question or fact that is in the class?

Answer 1

Three steps to accomplish what you want:
Know ahead of time or find out the number of questions you have to look through.
Create a random integer using arc4random() or some other method between 0 and that number.
Create a PFQuery on your question class with skip set to the random integer and limit set to 1.

Answer 2

Here is a function for retrieving your questions, only the first 1000, and saving them locally:
func saveAllObjectsLocally() {
let query = PFQuery(className: “Questions”)
query.limit = 1000
query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in
if error == nil {
if let objects = objects {
do {
try PFObject.pinAllInBackground(objects)
} catch let error as NSError? {
print("error \(error)")
}
}
} else {
print("Error: \(error!) \(error!.userInfo)")
}
}
}
Once they are saved locally, a random question can be selected:
func getRandomQuestion() -> PFObject? {
let query = PFQuery(className: “Questions”)
query.fromLocalDatastore()
query.findObjectsInBackgroundWithBlock {
(objects: [PFObject]?, error: NSError?) -> Void in
if let objects = objects {
let randomIndex = arc4random_uniform(UInt32(objects.count))
return objects[Int(randomIndex)]
}
}
return nil
}
This is going to be faster than accessing the network every time a random question is needed.
If you need to access the questions from the cloud you can add an index column to your Parse database and use that as a key to efficiently retrieve a random row.