On May 1, 2009, at 2:24 AM, Daniel Kennett wrote:
Thanks for your reply. Yes, I have code that triggers relationship
faults, and removing that code solves the problem. However, I need
that code to work! :-)
When fetching the data from the object tree, I call a method on the
pet instance called -pertinentActions. This method loops through
various relationships, calling -pertinentAction on each child
object. I've ruled out the -pertinentAction method, since calling -
className on the child objects also causes the crash to happen. I've
also double and triple checked my retains and (auto)releases and
they're all balanced.
My recommendation is don't check them *prove* them. If you release or
autorelease any vetvisit object, comment it out and see if the problem
goes away. I say this because I have had, and just about any
programmer probably has, stared at the exact glaring error over and
over again and not seen it.
In any case, there is an overrelease happening, which means somewhere
retains are *not* balanced, and 99.9999% of the time, it's the
programmer's code. But you have to find out how it is happening, so
it's time to bring out Instruments--it can tell you who is the culprit
and where it is.
On a different note, when you comment out the "for (VetVisit" code,
does it still crash on a VetVisit, or does it crash on a "Medication"
object?
Here's the code that triggers the crash:
-(NSArray *)pertinentActions {
NSMutableArray *actions = [[NSMutableArray alloc] init];
[actions addObject:[self birthdayAction]];
for (InsurancePolicy *policy in [self insurancePolicies]) {
KNClarusPertinentAction *action = [policy pertinentAction];
if (action) {
[actions addObject:action];
}
}
// If I return here, the later crash doesn't happen!
for (VetVisit *visit in [self vetVisits]) {
[visit className];
}
// Returning just after this...
for (Medication *medication in [self medications]) {
[medication className];
}
// ... or this causes the later crash.
return [actions autorelease];
}
Commenting out the for (VetVisit* and for (Medication* loops fixes
the crash. At this point, I'm doing no memory management at all -
the -pertinentActions method is being called thusly:
NSManagedObjectContext *context = [[NSManagedObjectContext alloc]
init];
Pet *pet = [KNClarusQuickDocumentParser petAtURL:url
inContext:context];
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setValue:[[[pet valueForKey:@"name"] copy] autorelease]
forKey:@"name"];
[dict setValue:[[[pet valueForKey:@"birthday"] copy] autorelease]
forKey:@"birthday"];
// More copying of strings and dates
[..]
[dict setValue:[[[pet valueForKey:@"pertinentActions"] copy]
autorelease] forKey:@"pertinentActions"]; // <--- Here
[context release];
return [dict autorelease];
I think I've stumbled upon a problem with the way I've set up my
model. The insurance policy collection, which doesn't crash after
being accessed, is simply a one-to-many relationship from pet.
However, the Medication and VetVisit relationships are a little more
complex. It goes:
Pet -> Medication(s) -> Medication Course(s) -> Medication Dose(s)
Pet -> Vet Visit(s)
The Medication Dose entity has an optional relationship to Vet Visit
in case the dose was given at a visit to the vet. Here's a
screenshot of that part of my model:
http://www.kennettnet.co.uk/stuff/ClarusModel.png
Right now, I'm at a dead-end. I've ruled out my memory management,
and can't see how I can work around what's happening, or what I'm
doing wrong!
Does the "Pet" class, or any class it has a relationship with,
release or autorelease any "VetVisit" object? I am assuming that
the "Pet" entity has a relationship to "VetVisit"--do you have any
code that would cause the relationship fault to fire? If so, what
happens when you comment that out?
On 29 Apr 2009, at 16:32, Alexander Spohr wrote:
Daniel,
You are trying to fetch an object and keep it - but you want to
ignore / throw away the NSManagedObjectContext. This will never
work. The NSManagedObjectContext keeps the object. Your Pet can
not exist without its NSManagedObjectContext.
You should let the caller provide a NSManagedObjectContext and
fetch your Pet into that context. Make it the callers
responsibility to get a NSManagedObjectContext not yours.
+ (Pet *)petAtURL:(NSURL *)url inContext:(NSManagedObjectContext
*)aManagedObjectContext
Or copy the pet into something like an NSDictionary and return
that.
atze
Am 29.04.2009 um 10:59 schrieb Daniel Kennett:
Hi list,
I'm hoping you guys can help me. I'm loading up a Core Data
store, copying some data out and attempting to clear it all up.
I use this code for my Quicklook plugin, and in parts of my app
for previewing documents in a more advanced manner than
Quicklook provides.
This is how I set up my ManagedObjectContext:
+(Pet *)petAtURL:(NSURL *)url {
NSManagedObjectModel *managedObjectModel =
[KNClarusQuickDocumentParser managedObjectModel];
NSPersistentStoreCoordinator *coordinator =
[[[NSPersistentStoreCoordinator alloc]
initWithManagedObjectModel:managedObjectModel] autorelease];
[coordinator addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:url
options:nil
error:&error];
NSManagedObjectContext *moc = [[NSManagedObjectContext alloc]
init];
// ^ Not Autoreleasing here. It's the responsibility of the
caller to release the MOC. Autoreleasing causes crashes.
[moc setPersistentStoreCoordinator:coordinator];
[[moc undoManager] disableUndoRegistration];
NSError *fetchError = nil;
NSArray *fetchResults;
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init]
autorelease];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"Pet"
inManagedObjectContext:moc];
[fetchRequest setEntity:entity];
fetchResults = [moc executeFetchRequest:fetchRequest
error:&fetchError];
if ((fetchResults != nil) && ([fetchResults count] == 1) &&
(fetchError == nil))
{
NSManagedObject *pet = [[fetchResults objectAtIndex:0] retain];
return [pet autorelease];
}
return nil;
}
And this is how I get the data out and release it:
Pet *pet = [KNClarusQuickDocumentParser petAtURL:url];
// Copy out some data.
NSManagedObjectContext *context = [pet managedObjectContext];
if (context) {
[context reset]; // This call results in EXC_BAD_ACCESS
[context setPersistentStoreCoordinator:nil];
[context release];
}
return [dict autorelease];
-------- End code --------
Different combinations of trying to do this right result in
crashes at different points. Leaving out [context reset] and
just releasing it obviously gives EXC_BAD_ACCESS again.
Autoreleasing the MOC in +petAtURL: causes crashes when the
autorelease pool pops. The only way I can get it to not crash is
to -init the MOC and never release or autorelease it, but that's
causing memory leaks!
Is there a good example anywhere of how to set up and tear down
a Core Data document correctly?
Keary Suska
Esoteritech, Inc.
"Demystifying technology for your home or business"
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