I am using Core Data to store a User entity which has a to many relationship to another entity (ScheduleDay). Every time I sync I use this line to reset the Ordered Set:
self.user.scheduleDays = [NSOrderedSet orderedSet];
My question is are the old days being deleted, or is there a better way to make sure I delete the old days as to not clutter up the NSManagedObjectContext or save too much unnecessary data.
No, this will not automatically delete these objects.
You have to manually delete them yourself prior to setting the scheduleDays to a new set.
To delete all the scheduleDays entities, you could do this for example:
NSManagedObjectContext *context = self.user.managedObjectContext;
for (NSManagedObject *object in self.user.scheduleDays)
{
[context delete:object];
}
self.user.scheduleDays = [NSOrderedSet orderedSet];
NSError *error;
[context save:&error];
if (error)
{
// Handle error
}
Related
So I am building in a hide function into my application. In my settings menu I have a UISwitch that should allow the user to hide themselves. I have created the UISwitch's IBAction like so:
-(IBAction)hideUserToggle:(id)sender {
AppDelegate *newAppDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [newAppDelegate managedObjectContext];
NSManagedObject *newOwner;
NSEntityDescription *entityDesc = [NSEntityDescription entityForName:#"LoggedInUser" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDesc];
NSManagedObject *matches = nil;
NSError *error;
NSArray *objects = [context executeFetchRequest:request error:&error];
newOwner = [NSEntityDescription insertNewObjectForEntityForName:#"LoggedInUser" inManagedObjectContext:context];
if (_hideUser.on) {
if ([objects count] == 0) {
NSLog(#"%#",[error localizedDescription]);
} else {
matches = objects[0];
[newOwner setValue:#"userHidden" forKeyPath:#"isHidden"];
NSLog(#"%#",[matches valueForKeyPath:#"isHidden"]);
}
} else {
if([objects count] == 0) {
NSLog(#"%#",[error localizedDescription]);
} else {
matches = objects[0];
[newOwner setValue:#"userNotHidden" forKeyPath:#"isHidden"];
NSLog(#"%#",[matches valueForKeyPath:#"isHidden"]);
}
}
}
This should set the value of the Core Data String that I use to determine whether a person is hidden or not, which I use later in my code as a conditional for loading data. However when I test this feature it doesn't seem to update the persistent data store (Core Data) when the user has flipped the switch. I have looked around everywhere and I found a reference to there being a delay in updating Core Data here -> Why does IOS delay when saving core data via a UIManagedDocument, however it doesn't seem to provide the answer to my problem.
I want to be able flip the switch and save that value so that when the user swipes over to another view controller it is immediately aware that the user has gone into "hiding" or offline so it does not show certain information.
A NSManagedObjectContext is a scratchpad. Changes you make within the context exist only within the context unless or until you save them to the context's parent (either the persistent store itself or another context).
You're not saving them. I'd assume you're therefore not seeing the change elsewhere because you're using different contexts. Meanwhile the change eventually migrates because somebody else happens to save.
See -save: for details on saving.
(aside: the key-value coding [newOwner setValue:#"userHidden" forKeyPath:#"isHidden"]-style mechanism is both uglier and less efficient than using an editor-generated managed object subclass; hopefully it's just there while you're debugging?)
I want to respond to changes of certain NSManagedObjects that have been added, updated, or deleted.
I have an issue with the deleted objects, though: all relationships to other objects are now nil.
Is there a way to get this kind of notification before the object is affected this way?
Edit:
This is basically my delete code:
[moc deleteObject:myObject];
id saveBlock = ^{
NSError *error = nil;
BOOL saved = NO;
saved = [self save:&error];
// error handling.
};
[moc performBlockAndWait:saveBlock];
If you are wanting to react to deletions then you should be listening for NSManagedObjectContextWillSaveNotification and watch for the NSDSeletedObjectsKey come through as part of the notification. That is the last chance before deletion to deal with them.
i am stuck with my first GCD and first core-data using application =)
two views access the same data (which is handled by a single DAO).
if i wait for the current view to finish loading its content no problem occors when changing view.
however: if i change the view (its tabbased) while one controller tries to fetch data from my model, the new controller tries the same and the threads 'collide' and my application freezes.
the freeze occurs in this line of code of my DAO:
NSArray *results = [managedObjectContext executeFetchRequest:fetch error:&error];
reloadAllMonth() accesses the fetch routine of my DAO
how i load the data in the first controller:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {
[self reloadAllMonth];
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self.allMonthTable reloadData];
});
in the second viewcontroller the first thing i do is update my DAO, this of course uses (beneath others) the very same fetch routine i called before:
[self.dataHandler updateData];
i have tried two approaches so far:
first using a c-semaphore:
-(NSArray *)fetchAllMonthExpenses{
//#return: array of all expenses in month (day & month type)
NSNumber *monthNumber = [self getMonthNumber:[NSDate date]];
NSEntityDescription *exp = [NSEntityDescription entityForName:#"Expense" inManagedObjectContext:managedObjectContext];
NSFetchRequest *fetch = [[NSFetchRequest alloc]init];
[fetch setEntity:exp];
[fetch setPredicate:[NSPredicate predicateWithFormat:#"month == %#",monthNumber]];
NSError *error = nil;
sem_wait(&isLoading);
NSArray *results = [self.managedObjectContext executeFetchRequest:fetch error:&error];
sem_post(&isLoading);
return results;
}
second using the synchronized directive
-(NSArray *)fetchAllMonthExpenses{
//#return: array of all expenses in month (day & month type)
NSNumber *monthNumber = [self getMonthNumber:[NSDate date]];
NSEntityDescription *exp = [NSEntityDescription entityForName:#"Expense" inManagedObjectContext:managedObjectContext];
NSFetchRequest *fetch = [[NSFetchRequest alloc]init];
[fetch setEntity:exp];
[fetch setPredicate:[NSPredicate predicateWithFormat:#"month == %#",monthNumber]];
NSError *error = nil;
#synchronized(self.class){
NSArray *results = [self.managedObjectContext executeFetchRequest:fetch error:&error];
return results;
}
}
sadly both of the approaches did not work, the application freezes whatever i do.
so my question is: what am i doing wrong (as i mentioned first time using threads), what am i missing, where should i look?
this has been keeping me busy for 2 days now and i cant seem to wrap my head around it :/
An NSManagedObjectContext and all of the NSManagedObjects inside it are not thread safe.
Whatever thread you use to create the context, that needs to be the only thread where you do anything relating to that context. Even just reading values from one of the managed object must be done on that thread and not on any other thread.
If you need two threads which both deal with the same database, you've got two options:
use dispatch_sync() to jump into the other thread momentarily to perform all read/write operations on the managed objects and/or the context
Or:
create a second NSManagedObjectContext in the other thread for the same database, and keep any changes made to the two contexts in sync.
The first option is much easier, but may remove much of the benefits of threading. The second option is harder, but it can be done, and there is a fairly good API for keeping two contexts on different threads in sync.
Lookup the Core Data Programming Guide for more details.
Inside my user object I have the following code to generate a new 'session' or continue the existing session if one exists.
Strangely it will keep other properties but just loses the 'user' property... user is in a one to many relationship with session, 1 user can have many sessions. (or will do, for the following test I am simply checking for any previous session and using it if it exists)
-(void)setupSessionStuff
{
// Create new Core Data request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Session" inManagedObjectContext:[self managedObjectContext]];
[request setEntity:entity];
// Create Sort Descriptors for request
NSSortDescriptor *startTimeSort = [[NSSortDescriptor alloc] initWithKey:#"startTime" ascending:NO selector:nil];
[request setSortDescriptors:[NSArray arrayWithObjects:startTimeSort, nil]];
[startTimeSort release];
[request setFetchLimit:1]; // Only get the most recent session
// Execute request
NSError *error = nil;
NSArray *results = [[self managedObjectContext] executeFetchRequest:request error:&error];
if (results == nil) {
// Something went horribly wrong...
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
exit(-1);
}
[request release];
Session *theSession = nil;
if ([results count] == 1) {
NSLog(#"existing session");
// Use existing Session
theSession = [results objectAtIndex:0];
NSLog(#"session.user: %#", [theSession valueForKey:#"user"]); // this is always null!
} else {
NSLog(#"new session");
// Create new Sesson
theSession = (Session *)[NSEntityDescription insertNewObjectForEntityForName:#"Session" inManagedObjectContext:[self managedObjectContext]];
// Add the Session to the User
NSLog(#"before: session.user: %#", theSession.user); // null
theSession.user = self;
NSLog(#"after: session.user: %#", theSession.user); // looks good
}
...
NSLog(#"before.save: session.user: %#", theSession.user); // good
// Save everything
error = nil;
if (![[self managedObjectContext] save:&error]) {
// Something went horribly wrong...
NSLog(#"Unresolved error: %#, %#, %#", error, [error userInfo],[error localizedDescription]);
exit(-1);
}
NSLog(#"after.save: session.user: %#", theSession.user); // still there..
}
Additionally I have opened up the Core Data sqlite file and examined with SQLite Manager. It looks like the relationship has been correctly saved, as I can see the userID stored in the session table.
-
Just added this at the start of my method as another test.
NSSet *set = self.session;
for(Session *sess in set) {
NSLog(#"startTime %#", sess.startTime);
NSLog(#"user %#", sess.user);
}
Strangely enough the user is set in this case!? So set here then not set a few lines later when I do the fetch request... ?
-
In response to feedback below
Have added this code after assigning session.user = self and both return the expected output. So it does look like the problem is with the subsequent fetch.
NSLog(#"self.session: %#", self.session);
NSLog(#"self.session: %#", [self valueForKey:#"session"]);
Also I agree that accessing my session's through self.session will let me work around my issue, but it doesn't solve what is going on here.
In other places I surely won't be able to walk from one entity to the other so need to confidence the fetch is going to pull everything in correctly.
Firstly, I would check that the relationship is set from the other side by logging self.session. If that shows as null then you have no reciprocal relationship set in the model.
I think that your fetch is poorly constructed. You are relying on the sort descriptor to provide the last used session but you only have a fetch limit of 1. You seem to think that the fetch will find all existing Session objects, sort them and then return the first one. However, sorts execute last so the fetch will find a single session object (because of the fetch limit) and will then apply the sort to that single object. This makes it likely that you will be dealing with a more or less random Session object.
You probably don't need a fetch at all because you are only interested in the Session objects in a relationship with the User object which is self. If you already have the object in one side of a relationship, you don't need to fetch, you just need to walk the relationship. All you really need to do is:
if ([self.session count]==0){
//...create new session and set relationship
}else{
//... find latest session
}
I think your problem with this particular chunk of code is in the reporting. When you get a return value, you use the self.user notation but where you get a null return you use valueForKey:.
While in theory both return the same value, they don't have to because they don't use the same mechanism to return the value. The self-dot notation calls an accessor method while valueForKey: may or may not depending on the specifics of a class' implementation. I would test if the self.session returns a value where valueForKey: does not.
Well I found the problem and solved my issue...
After examining the memory address of my session entity I noticing that it was changing between runs. Investigating further I discovered that where I had been testing some code earlier in another class, creating a new session entity, but not saving it, well, it was being saved after all - when I issued the save in my code above!
I've looked through all the class documentation for Core Data and I can't find away to programmatically update values in a core data entity. For example, I have a structure similar to this:
id | title
============
1 | Foo
2 | Bar
3 | FooFoo
Say that I want to update Bar to BarBar, I can't find any way to do this in any of the documentation.
In Core Data, an object is an object is an object - the database isn't a thing you throw commands at.
To update something that is persisted, you recreate it as an object, update it, and save it.
NSError *error = nil;
//This is your NSManagedObject subclass
Books * aBook = nil;
//Set up to get the thing you want to update
NSFetchRequest * request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:#"MyLibrary" inManagedObjectContext:context]];
[request setPredicate:[NSPredicate predicateWithFormat:#"Title=%#",#"Bar"]];
//Ask for it
aBook = [[context executeFetchRequest:request error:&error] lastObject];
[request release];
if (error) {
//Handle any errors
}
if (!aBook) {
//Nothing there to update
}
//Update the object
aBook.Title = #"BarBar";
//Save it
error = nil;
if (![context save:&error]) {
//Handle any error with the saving of the context
}
The Apple documentation on using managed objects in Core Data likely has your answer. In short, though, you should be able to do something like this:
NSError *saveError;
[bookTwo setTitle:#"BarBar"];
if (![managedObjectContext save:&saveError]) {
NSLog(#"Saving changes to book book two failed: %#", saveError);
} else {
// The changes to bookTwo have been persisted.
}
(Note: bookTwo must be a managed object that is associated with managedObjectContext for this example to work.)
Sounds like you're thinking in terms of an underlying relational database. Core Data's API is built around model objects, not relational databases.
An entity is a Cocoa object—an instance of NSManagedObject or some subclass of that. The entity's attributes are properties of the object. You use key-value coding or, if you implement a subclass, dot syntax or accessor methods to set those properties.
Evan DiBiase's answer shows one correct way to set the property—specifically, an accessor message. Here's dot syntax:
bookTwo.title = #"BarBar";
And KVC (which you can use with plain old NSManagedObject):
[bookTwo setValue:#"BarBar" forKey:#"title"];
If I'm understanding your question correctly, I think that all you need to keep in mind is managed objects are really no different than any other Cocoa class. Attributes have accessors and mutators you can use in code, through key value coding or through bindings, only in this case they're generated by Core Data. The only trick is you need to manually declare the generated accessors in your class file (if you have one) for your entity if you want to avoid having to use setValue:ForKey:. The documentation describes this in more detail, but the short answer is that you can select your attributes in the data model designer, and choose Copy Obj-C 2.0 Method Declarations from the Design menu.
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSArray *temp = [[NSArray alloc]initWithObjects:#"NewWord", nil];
[object setValue:[temp objectAtIndex:0] forKey:#"title"];
// Save the context.
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
I think this piece of code will give you the idea ;)