Error with core data fetch requests: subentitiesByName misapplied, and segfaults

FROM : Niko Matsakis
DATE : Thu Jul 20 16:58:03 2006

Dear all,

I recently started hacking on a small "accounting" application using 
Core Data.  It contains almost no code yet, but I'm running into 
crashes and other strange behavior when trying to use a fetch 
request.  What is most strange is that if I build the same fetch 
request by hand, rather than using a stored fetch request, everything 
works fine.

The code in question attempts to select all instances of the class 
"Expense" that have a given payee; at first, the payee was set by 
variable, but at the moment I have it hard-coded for testing purposes.

When I build the fetch request by hand, it seems to work.  When I 
execute a saved fetch request, I get the following error:

> 2006-07-20 15:15:20.087 drachma[849] *** -[NSKeyBindingManager 
> subentitiesByName]: selector not recognized [self = 0x33f6b0]


or one like it.  Sometimes the class which does not recognize the 
selector is a dictionary, other times a string.  Sometimes I simply 
get a SEGFAULT or BUS error.

I tried to create a new project but was unable to reproduce the problem.

Any ideas?  I can't find *anything* online discussing this sort of flaw.

The project can be downloaded from http://smallcultfollowing.com/code/
drachma.tar.gz; it uses a few debugging print out routines from a 
library, Oaxaca, that I've been accumulating.  They are included.  To 
reproduce the problem, simply open, build and run the project, and 
then click on the "Clear" button.  This performs a query in two 
different ways.  You'll see that the first will work, and the second 
(stored query) will fail.

The code performing the query itself is in "drachma/src/
DrachmaController.m" in the method "clearNewExpense:".  Here is the 
content of that method:

- (IBAction)clearNewExpense:(id)sender
{
   // ... some irrelevant code skipped ...

    // *** CONSTRUCT THE QUERY BY HAND ***
    NSManagedObjectContext *moc = [_drachma managedObjectContext];
    NSEntityDescription *entityDescription = [NSEntityDescription
    entityForName:@"Expense" inManagedObjectContext:moc];
    NSFetchRequest *request = [[[NSFetchRequest alloc] init] 
autorelease];
    [request setEntity:entityDescription];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:
        @"payee == %@", @"Migros"];
    [request setPredicate:predicate];
    NSError *error = nil;
    NSArray *array = [moc executeFetchRequest:request error:&error];

    // ** EXECUTE STORED QUERY (this fails) **
    NSManagedObjectModel *model = [_drachma managedObjectModel];
    NSFetchRequest *fetchRequest =
        [model fetchRequestFromTemplateWithName:@"specific"
                          substitutionVariables:[NSDictionary 
dictionary]];
    array = [moc executeFetchRequest:fetchRequest
                                error:&error]; // ** EXCEPTION OCCURS 
HERE **
}

It may be relevant that I use a distinct class for each type of 
Entity.  However, I have changed this back and forth and it seems to 
make no difference either way.

Thank you for any help!  I apologize for the scatter-brained email, 
I'm at a bit of a loss as to how to proceed in debugging this.  I 
have reproduced it on multiple machines, but my attempts to narrow it 
down have been unsuccessful.  Still, I have spent a total of a few 
hours working on the project, so it's a fairly constrained example 
even as is.


Niko