Getting 'This query has an outstanding network connection.' - objective-c

Question

I'm getting 'This query has an outstanding network connection.'
I know only one query is allowed at time and I think that's what I'm doing here but apparently not..
retrieveFromParse is at viewDidLoad.
-(void) retrieveFromParse{
PFQuery *query = [PFQuery queryWithClassName:self.parseClassName];
[query whereKey:#"photo" equalTo:[PFObject objectWithoutDataWithClassName:#"photoObject" objectId:self.currentObjectID]];
[query orderByDescending:#"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
NSLog(#"Successfully retrieved %d scores.", (int)objects.count);
// Do something with the found objects
for (PFObject *object in objects) {
NSLog(#"%#", object.objectId);
self.commentArray = [object objectForKey:#"comment"];
}
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
// If no objects are loaded in memory, we look to the cache
// first to fill the table and then subsequently do a query
// against the network.
if ([self.objects count] == 0) {
query.cachePolicy = kPFCachePolicyCacheThenNetwork;
}
}
- (id)initWithStyle:(UITableViewStyle)style currentObjectID:(NSString*) currentObjectID {
self = [super initWithStyle:style];
if (self) {
self.currentObjectID = currentObjectID;
self.parseClassName = #"extra";
self.pullToRefreshEnabled = YES;
self.paginationEnabled = NO;
self.objectsPerPage = 25;
}
return self;
}

Answer 1

The problem is here:
if ([self.objects count] == 0) {
query.cachePolicy = kPFCachePolicyCacheThenNetwork;
}
You're calling that after you make the call in the background. In other words, you are trying to modify a query that is currently being made while it's being made in the background - triggering the error. Try this instead:
-(void) retrieveFromParse{
PFQuery *query = [PFQuery queryWithClassName:self.parseClassName];
[query whereKey:#"photo" equalTo:[PFObject objectWithoutDataWithClassName:#"photoObject" objectId:self.currentObjectID]];
[query orderByDescending:#"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
NSLog(#"Successfully retrieved %d scores.", (int)objects.count);
// Do something with the found objects
for (PFObject *object in objects) {
NSLog(#"%#", object.objectId);
self.commentArray = [object objectForKey:#"comment"];
}
} else {
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
// If no objects are loaded in memory, we look to the cache
// first to fill the table and then subsequently do a query
// against the network.
if ([self.objects count] == 0) {
query.cachePolicy = kPFCachePolicyCacheThenNetwork;
}
}];
}