I am wanting to set up a basic relationship with two entities in Core Data, but the relationship is either not saving, or is not working properly and I'm not sure why.
The two entities are Character and Avatar, its a one-to-one relationship. A character can have 1 avatar. Technically, it should be a "one avatar can be owned by many characters", but I'll deal with that later.
I want to add characters and assign them an avatar.
There are already 10 avatars in Core Data and 1 character, both of which I've verified via the Terminal and SQLite.
The problem is, I'm having troubling "finding an avatar by a name and then saving the relationship to a character".
So far,
I set up a fetch request called: "frqAvatarWithName" where the Predicate has the following structure:
[quote]
name == $AVATAR_NAME
[/quote]
This is so: I can find an avatar with a certain name; and then I can create a relationship with a character.
Issue 1: It gets to execute the query but then never displays how many records there are.
I get a EXC_BAD_ACCESS error in debug mode and I have traced it back to the fetch request template handling -- so, this must be in error or I have done it wrong.
Issue 2: I am not sure if I am even setting up this "basic" relationship up properly.
[code]
// This code is meant to find an avatar with a certain name and then save the relationship
// between a character and said avatar.
// This is my app delegate file for the moment
// All the files are present, and I have deleted/recreated the app various times
-(void)characterMaker
{
NSLog(#"Inside characterMaker...");
NSError *error = nil;
NSManagedObjectContext *context = [self managedObjectContext];
NSManagedObjectModel *model = [self managedObjectModel];
// Find an avatar with a specific name
NSString *nameToFind = #"avt_player_1";
// Use a Fetch request template
NSDictionary *subs = [NSDictionary dictionaryWithObjectsAndKeys:nameToFind, #"AVATAR_NAME", nil];
NSFetchRequest *fetchRequest = [model fetchRequestFromTemplateWithName:#"frqAvatarWithName"
substitutionVariables:subs];
// Set the entity to use
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Avatar"
inManagedObjectContext:context];
[fetchRequest setEntity:entity];
// Execute the query (it never even reaches this point)
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects == nil) {
// Handle the error
NSLog(#"Error -- %#", [error localizedDescription]);
abort();
}
NSLog(#"Found %# records", [fetchedObjects count]);
// Print out avatar names
for (Avatar *a in fetchedObjects)
{
NSLog(#"Name = %#", [a valueForKey:#"name"]);
}
// This is where I would use `a` and store it in a character entity, and thus create the relationship
[/code]
I gave up on this and did the whole project with the FMDatabase project and SQLite; I've been able to resolve the problem this way.
Thread closed.
Related
I have a pretty weird problem. I'm using coredata to save notes. I can access/save/edit all the attributes of the "Notes" entity, besides one : category.
-(void)editCategory {
NSFetchRequest *request = [[NSFetchRequest alloc]init];
NSEntityDescription *categRequest = [NSEntityDescription entityForName:#"Notes" inManagedObjectContext:_managedObjectContext];
request.predicate = [NSPredicate predicateWithFormat:#"text = %#", noteToEdit];
[request setEntity:categRequest];
//Error handling
NSError *error = nil;
NSMutableArray *mutableFetchResults = [[_managedObjectContext executeFetchRequest:request error:&error]mutableCopy];
if (mutableFetchResults == nil) {
NSLog(#"Error happened : %#", error);
}
Notes *editMe = [mutableFetchResults objectAtIndex:0];
[editMe setCategory:editCategoryText];
NSLog(#"Category from pickerview : %#", editCategoryText);
if (![_managedObjectContext save:&error]) {
NSLog(#"couldnt save : %#", error);
}
}
This line :
[editMe setCategory:editCategoryText];
is crashing. editCategoryText is a string, as the category attribute. The weird thing is that I'm using the exact same piece of code to change the title attribute, and I don't have any problem.
Log file :
2013-11-07 15:49:20.286 Simple Notes 1[16511:a0b] -[__NSCFString managedObjectContext]: unrecognized selector sent to instance 0x8dccc30
2013-11-07 15:49:20.293 Simple Notes 1[16511:a0b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString managedObjectContext]: unrecognized selector sent to instance 0x8dccc30'
Do you have any idea why this attribute is behaving differently from the others ? Thank you.
Not at a computer so can't test this but:
Get rid of the mutableCopy. executeFetchRequest returns autoreleased objects, which you are then trying to copy, this turns into a garbage pointer, which happens to end up pointing to a string.
Actually it seems like it was a core data bug, I solved it by deleting my app in the simulator, deleting the core data model in xcode, built it again and performed a clean.
Setup: I have a collection of parent objects, call them ObjectA. Each ObjectA has a one-to-many relation to ObjectB. So, one ObjectA may contain 0..n ObjectB-s, and each ObjectB has a specific ObjectA as its parent.
Now, I would like to do a Core Data fetch of ObjectA-s, where they are sorted by their latest ObjectB. Is it possible to create a sort descriptor for that?
There is a related question that describes exactly the same situation. The answer suggests denormalizing the attribute from ObjectB into ObjectA. This would be OK if there really is no way to do this with one fetch request.
The related question also mentions:
Actually, I just had an idea! Maybe I can sort Conversations by messages.#max.sortedDate…
I tried. It doesn’t seem to be possible. I get this error:
2012-10-05 17:51:42.813 xxx[6398:c07] *** Terminating app due to uncaught
exception 'NSInvalidArgumentException', reason: 'Keypath containing
KVC aggregate where there shouldn't be one; failed to handle
ObjectB.#max.creationTime'
Is denormalizing the attribute into ObjectA the only/best solution?
You could add an attribute in ObjectB which is the time stamp of the add date, then in the fetch request you can do something like this:
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:#"objectB.addTime" ascending:YES];
...
fetchRequest.sortDescriptors = #[descriptor];
I know this question is a bit old but what I did was get all ObjectBs, iterate over the results and pull out the ObjectB property and add it to a new array.
NSFetchRequest *fetchRequest = [NSFetchRequest new];
[fetchRequest setEntity:self.entityDescForObjectB];
// sort
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"date" ascending:YES];
[fetchRequest setSortDescriptors:#[sortDescriptor]];
NSError *error = nil;
NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects == nil) {
NSLog(#"Error fetching objects: %#", error.localizedDescription);
return;
}
// pull out all the ObjectA objects
NSMutableArray *tmp = [#[] mutableCopy];
for (ObjectB *obj in fetchedObjects) {
if ([tmp containsObject:obj.objectA]) {
continue;
}
[tmp addObject:obj.objectA];
}
This works because CoreData is an object graph so you can work backwards. The loop at the end basically checks to see if the tmp array already has a specific ObjectA instance and if not adds it to the array.
It's important that you sort the ObjectBs otherwise this exercise is pointless.
I have an NSPersistentDocument subclass using NSManagedObject subclasses for my data.
When a new document is opened, I do some initializing of data structures (trivial amount of populating fields). What I've noticed is that the Untitled document gets autosaved, and when the application re-opens, that document gets loaded. If the application quits, the user doesn't (by default) get prompted with the save dialog. If the window closes, the user does.
First question:
I want to call up the save dialog when the user quits the application. I don't want this Untitled document hanging around (under normal circumstances). I either want it saved or trashed.
I attempted to fill out:
- (void)applicationWillTerminate:(NSNotification *)aNotification
In order to trigger the document to be saved. Calling save: on the context at this point gives an error. From what I can tell, this is because the user hasn't yet saved the file on their own. In addition, calling [self close]; or [[self windowForSheet] close]; close the window without saving.
How can I force the save dialog to come up? How can I trash the untitled document?
Second question (no, I can't count):
Since when the application starts, there may or may not be an Untitled document to deal with, I'm trying to keep track of the state in another model. I've already found that the initial data (to which I referred earlier) is present when the Untitled document came up. My other model has some metadata, including a success flag/state for the populated data. Once the populated data is all in place and correct, the state indicates as such. Unfortunately, while my populated data is being loaded when the app starts with a pre-existing Untitled document, the metadata class is not.
Please excuse the roughness of the code, at this point, I'm mucking it up until I can see that it's working how I want before I polish it back off:
- (bool) createGameState {
NSEntityDescription* description = [NSEntityDescription entityForName:[GameState name] inManagedObjectContext:[self managedObjectContext]];
NSFetchRequest* req = [[NSFetchRequest alloc] init];
[req setEntity:description];
NSError *error = nil;
NSArray *array = [[self managedObjectContext] executeFetchRequest:req error:&error];
[req release];
req = nil;
GameState* result = nil;
if (array) {
NSUInteger count = [array count];
if (!count) {
// Create the new GameState.
DebugLog(#"Creating GameState");
result = [NSEntityDescription insertNewObjectForEntityForName:[GameState name] inManagedObjectContext:[self managedObjectContext]];
[result setIsLoaded:[NSNumber numberWithBool:NO]];
} else {
if (count > 1) {
NSLog(#"WARNING: Potentially Corrupt Game State. found: %lu", count);
}
result = [array objectAtIndex:0];
if ([result isLoaded]) {
[self variantLoaded];
} else {
// In this case, we have an aborted set-up. Since the game isn't
// playable, just refuse to create the GameState. This will
// force the user to create a new game.
return NO;
}
}
} else {
DebugLog(#"error: %#", error);
}
[game setState:result];
return result;
}
Note that array is always present, and count is always zero. No, I'm not explicitly calling save: anywhere. I'm relying on the standard auto-save, or the user performing a save.
EDIT:
I installed the Core Data Editor app. It turns out the issue isn't on saving the data, but on loading it. (Note: Due to another issue, the app saves as binary when instructed to save as XML, which causes much head banging.)
I've broken it down to the simplest code, which should pick up all objects of type GameState in an array. It retrieves none, despite there clearly being objects of the appropriate type in the saved file:
NSManagedObjectContext* moc = [self managedObjectContext];
NSEntityDescription* entity = [NSEntityDescription entityForName:#"GameState" inManagedObjectContext:moc];
NSFetchRequest* req = [[NSFetchRequest alloc] init];
[req setEntity:entity];
NSError *error = nil;
NSArray *array = [moc executeFetchRequest:req error:&error];
Array is not null, but [array count] is 0.
At this point, I'm guessing it's something simple that I'm overlooking.
Second EDIT:
I added -com.apple.CoreData.SQLDebug 5 and saved as SQLite. The call to executeFetchRequest does not generate any debug logs. I do see the INSERT INTO ZGAMESTATE entry show up in the logs. It seems that executeFetchRequest is not getting passed to the backend.
Third EDIT (this one burns):
I created a new xcode project, using core data (as I had with the other). I copied just this one function (stubbing where necessary) and plopped a call to it in windowControllerDidLoadNib. In this new project, the code above works.
Found the problem.
I errantly was loading objects in Document's - (id) init call. Moved to windowControllerDidLoadNib (which is what I did in the test version) and it worked fine.
I have a one to many relationship in my core data model. I need to create a new entity and save it. The entity has a one to many relationship which generated the following code:
- (void)addRelationshipEvent1:(NSSet *)values;
- (void)removeRelationshipEvent1:(NSSet *)values;
.
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
ApplicationRecord *newManagedObject = (ApplicationRecord*)[NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
newManagedObject.startDate = [NSDate date];
newManagedObject.stopDate = [[NSDate date] dateByAddingTimeInterval:120];
//keep adding individual dynamic properties
is it correct to set the -toMany relationship sets to nil initially? Or do I need to initialize an (empty?) set here and assign it? Would I be able to add extra objects later if I set the initial set to nil?
newManagedObject.relationshipEvent1 = nil;
newManagedObject.relationshipEvent2 = nil;
//...
// Save the context.
NSError *error = nil;
if (![context save:&error])
{
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
Alex,
You don't need to intialize your relationships. Just use the supplied accessors or helper functions and Core Data takes care of it. IOW, only worry about the property/relationship when you need to actually use it.
Andrew
Is there a way to inspect a NSPredicate object for the purposes of serializing it into a URL? I am trying to retrieve the data remotely and need to translate the predicate object into a URL with querystring parameters that the server understands.
This was inspired by a talk given in WWDC 2010 called "Building a Server Driven User EXperience" where the speakers talk about using Core-Data and with a server backend. I have followed the session video and slides, but am stuck on the serializing point. For example, there is a Person object, and I'm trying to fetch all people whose first name is "John". I am using a subclass of NSManagedObjectContext called RemoteManagedObjectContext, which overrides the executeFetchRequest method, and is supposed to send the call to the server instead. The fetch request is being created as (ellipsed non-essential parts):
#implementation PeopleViewController
- (NSArray *)getPeople {
RemoteFetchRequest *fetchRequest = [[RemoteFetchRequest alloc] init];
NSEntityDescription *entity = ...
NSPredicate *template = [NSPredicate predicateWithFormat:
#"name == $NAME AND endpoint = $ENDPOINT"];
NSPredicate *predicate = [template predicateWithSubstitutionVariables:...];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
NSError *error = nil;
// the custom subclass of NSManagedObjectContext executes this
return [remoteMOC executeFetchRequest:fetchRequest error:&error];
}
#end
Now inside the custom subclass of NSManagedObjectContext, how can I serialize the fetch request into querystring parameters suitable for the server. So given the above fetch request, the corresponding URL would be:
http://example.com/people?name=John
It is possible to get a string representation of the predicate which returns,
name == "John" AND endpoint == "people"
that I can parse to get the parameters name, and endpoint. However, is it possible to do it without parsing the string? Here's a partial implementation of the RemoteManagedObjectContext class.
#implementation RemoteManagedObjectContext
- (NSArray *)executeFetchRequest:(NSFetchRequest *)request error:(NSError **)error {
// this gives name == "John" AND endpoint == "people"
// don't know how else to retrieve the predicate data
NSLog(#"%#", [[request predicate] predicateFormat]);
...
}
#end
Even better than a string representation is an object-oriented representation! And it's done automatically!
First, check the class of the NSPredicate. It will be an NSCompoundPredicate. Cast it to an appropriate variable.
You'll then see that it's compoundPredicateType is NSAndPredicateType, just like you'd expect.
You can also see that the array returned by -subpredicates reveals 2 NSComparisonPredicates.
The first subpredicate has a left expression of type NSKeyPathExpressionType and a -keyPath of #"name", the operator is NSEqualToPredicateOperatorType. The right expression will be an NSExpression of type NSConstantValueExpressionType, and the -constantValue will be #"John".
The second subpredicate will be similar, except that the left expression's keyPath will be #"endpoint", and the right expression's constantValue will be #"people".
If you want more in-depth information on turning NSPredicates into an HTTP Get request, check out my StackOverflow framework, "StackKit", which does just that. It's basically a framework that behaves similarly to CoreData, but uses StackOverflow.com (or any other stack exchange site) to retrieve information. Underneath, it's doing a lot to convert NSPredicate objects into a URL. You're also welcome to email me any specific questions you have.