Random function in Core Data Xcode - objective-c

Question

Im a new programmer trying to make a random function using Core Data. What I want is for the label to return a random managedObject from my entity. Here is my code
- (IBAction)randomize{
NSEntityDescription *entitydesc = [NSEntityDescription entityForName:#"Restraunt" inManagedObjectContext:context ];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
[request setEntity:entitydesc];
NSError *error;
NSArray *matchingData = [context executeFetchRequest:request error:&error];
NSString *textString;
int RandomNumber;
RandomNumber = arc4random() %[matchingData count];
textString = [matchingData objectAtIndex:RandomNumber];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"restraunt_name like %#",textString];
[request setPredicate:predicate];
if(matchingData.count <= 0){
self.label.text = #"doesnt exist";}
else {
NSString *string;
for (NSString *obj in matchingData){
string = [obj valueForKey:#"restraunt_name"];
}
self.label.text = [NSString stringWithFormat:#" %#", string] ;
}
}

Answer 1

There are several things wrong in this code. For instance, "textString" is not a string, it's one of your Restraunt entities. Also, the for loop you have in the else clause just loops through all you entities (making your random selection irrelevant), so "string" will be the last restaurant name in your data. Your code should look something like this,
- (IBAction)randomize{
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Restraunt"];
NSError *error;
NSArray *matchingData = [context executeFetchRequest:request error:&error];
int randomNumber = arc4random() %[matchingData count];
NSManagedObject *aRestraunt = matchingData[randomNumber]; // aRestraunt might not be an NSManagedObject depending on whether you've subclassed NSManagedObject or not -- if you have, then that should probably be Restraunt instead.
self.label.text = [aRestaurant valueForKey:#"restraunt_name"];
}
After Edit:
The answer I provided above was basically a "fix up" of your code to make it work. However, it's not the most efficient way to get a single random object. There's no need to fetch all the objects into memory just to get one. Instead you can get the count of your records as Hal Mueller suggested in his comment, then use the fetchOffset in combination with the fetchLimit to get one record,
NSError *error;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Restraunt"];
NSUInteger count = [context countForFetchRequest:request error:&error];
if (! error) {
NSUInteger rand = arc4random_uniform() % count;
[request setFetchOffset:rand];
[request setFetchLimit:1];
NSError *fetchError;
NSManagedObject *aRestraunt = [[context executeFetchRequest:request error:&fetchError] lastObject];
if (! fetchError) {
self.label.text = [aRestaurant valueForKey:#"restraunt_name"];
}else{
NSLog(#"There was an error in fetching a Restraunt entity");
}