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iOS

Posted by Kevin Duck
Kevin Duck
5,502 Points

Parse method causing "uncaught exception 'NSInvalidArgumentException', reason: 'Cannot do a comparison query for (null)'

When I run the self-destructing messaging app, I get "Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot do a comparison query for type: (null)'" It seems to be related to [PFInternalUtils assertValidClassForQuery:] .

When I comment out the following code from inboxViewController.m, I can launch the app and log in: 

PFQuery *query = [PFQuery queryWithClassName:@"Messages"];
    [query whereKey:@"recipientIds" equalTo:[[PFUser currentUser] objectId]];
    [query orderByDescending:@"createdAt"];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (error) {
            NSLog(@"error %@ %@", error, [error userInfo]);
        } else {
            self.messages = objects;
            [self.tableView reloadData];
            NSLog(@"Got %d messages", [self.messages count]);
        }
    }];

And then I can uncomment the code and run the app in the simulator/ device properly. It's almost like it crashes because it forgot whether I was logged in or something? It looks like I'm not the only one: https://www.parse.com/questions/ios-most-elegant-way-to-catch-assertvalidclassforquery-problems But this didn't help. Any idea?

3 Answers

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

looks like the currentUser object id here

[query whereKey:@"recipientIds" equalTo:[[PFUser currentUser] objectId]

is null. see if there is a reason why that is happening. Are you logged in?

Kevin Duck
Kevin Duck
5,502 Points
Kevin Duck
Kevin Duck
5,502 Points

When I comment out the code and run it, I can log in, after which the whole app works. Strangely enough, I added an if statement to check whether the objectid is nil:

- (void) viewWillAppear:(BOOL)animated {

    [super viewWillAppear:animated];

    PFQuery *query = [PFQuery queryWithClassName:@"Messages"];
    // prevents error when running for first time in a while
    if ([[PFUser currentUser] objectId] == nil) {
        NSLog(@"No objectID");
    } else {
    [query whereKey:@"recipientIds" equalTo:[[PFUser currentUser] objectId]];
    [query orderByDescending:@"createdAt"];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (error) {
            NSLog(@"error %@ %@", error, [error userInfo]);
        } else {
            self.messages = objects;
            [self.tableView reloadData];
            NSLog(@"Got %d messages", [self.messages count]);
        }
    }];
    }
}

And now it works. Can't explain that.

Hamish Lockie
Hamish Lockie
5,088 Points

This makes sense.

If you're not logged in then it will skip making this query call. If you are logged in it will make the call.

Thanks for posting.

Charles Leclercq
Charles Leclercq
4,614 Points
Charles Leclercq
Charles Leclercq
4,614 Points

I think the if() prevents the code to run the rest of the query and therefor avoids the crash.