Quick question, if I want to replace a to-many relationship completely. Do I need to delete all the previous objects, or is that done automatically
newVariable.hasRel = [NSSet setWithSet:newSet];
Where the variable has had some objects in that set, will just replacing it with the new set get rid of the old entities ???
Quick answer: Assigning a new set of related objects does not delete the previously related objects. You have to do that manually.
Related
This is a follow up to an earlier question: Core Data: change delete rule programmatically.
I'd like to rephrase my question, and will do that here.
Briefly, my app allows updating entries from a 3rd party database, but I'd like to keep user annotations. So my workflow is:
iterate over all entities
download external xml and parse it into a new entity
if user annotations, change their relationship from old entity to new entity
delete old entity
During the import, the old entity is in the main context, the new entity is in a temporary import context.
Number 3 gives me problems, if I just change the relationship, then they don't show if I update my UI. If I use the objectID to get the annotation and then change the relationship as follows:
NSManagedObjectID *objectId = oldAnnotation.objectID;
Annotation *newAnnotation = [importContext objectWithID: objectId];
[newEntry addAnnotationObject: newAnnotation];
It's still not working - it's not showing up.
EDIT: if I change the context in the second line to newEntry.managedObjectContext, I get an Illegal attempt to establish a relationship 'foo' between objects in different contexts error.
What am I missing?
UPDATE: After some late-night hair-pulling debugging, I found that I when I was fetching the newEntry, I was actually fetching the oldEntry, therefore none of the changes would show up. The answer below by #Mundi pointed me in the right direction.
Copying the old annotations worked using my code above, followed by copying the attributes. For some user input with relationships in itself, I had to do a "Deep Copy", which I found here: How can I duplicate, or copy a Core Data Managed Object?.
I think creating a new entity and deleting the old one is a problematic strategy. You should try to properly update the existing entities and only create new ones if they do not yet exist.
Whenever I need an object from a different context, I fetch it. That being said, your object id code should work. However, there could be all sorts of other glitches, that you should check:
Did you save the importContext?
Did you save its parent context, presumably the main context?
Was the modified object graph saved to the persistent store?
Are you checking the results after you have saved?
It try to remove items from to-many relationship like this:
(application.selectedDiagrams as! NSMutableOrderedSet).removeObjectsInRange(NSMakeRange(1, 2))
mainMOC.save(nil)
After I carry out commands, it seems to work, but latter deleted items appears again. Why?
You are probably running into a Swift versus Objective-C conflict. You are much better off using the standard Core Data add and remove objects methods. Hence, create an array with the objects you would like to remove and then pass it to remove<Type>Objects:.
I am running into an issue with CoreData (using MagicalRecord) trying to change an attribute. I think this is the result of the object having relationships to two parent entities.
The object is a manual, this has a to-many relationship to both a car and library. The library contains all manual objects. A car has 1-3 manual items.
Every manual has a UID and the same object is shared between the car and library.
For some reason, once the object is set into the relationship for both, I cannot change the title (NSString) attribute of the manual.
I checked to make sure I am in the same context. Not sure what the issue is.
This is what I am logging:
NSLog(#"Manual Title: %#",manual.title);
//prints Old Manual
manual.title = #"New Manual"
NSLog(#"Manual Title: %#",manual.title);
//prints New Manual
I'm saving this inside a MagicalRecord saveUsingCurrentThreadContextWithBlockAndWait other unrelated NSManagedObjects in the same method are being saved.
When the app loads the data into the UI, it still reads "Old Manual"
Any suggestions?
Thank you for your time.
It turns out the issue was two-fold with the MagicalRecord methods I was using:
1) Instead of saveUsingCurrentThreadContextWithBlockAndWait I should have used saveWithBlockAndWait
2) When I was fetching the manual object, I wasn't passing the context, so I changed MR_findFirstWithPredicate to MR_findFirstWithPredicate:inContext
Hopefully this will save someone else some time
In the documentation and in the broad literature the generated factory method to delete/remove a subclassed managed object in CoreData for IOS is
(void)removeXXXObject:(NSManagedObject *)value
where XXX is the corresponding relationship or we can use simply removeObject.
In my code I used this:
Data *lastData = [[self sortedPersonDatas] objectAtIndex:0];
[selectedPerson removePersonDatasObject:lastData];
where PersonDatas is a one-to-many relationship to Data managed object from I took the last data (lastData resulted from a sorted array of all data)
But using the first two remove methods and checking the SQL database behind we can find that the actual data is existing just the inverse relationship is null.
To completely delete the data (all attributes and the object) I had to use:
[selectedPerson.managedObjectContext deleteObject:lastData];
The question: which is the better method and is it correct that CoreData leaves the data intact?
removeXXXObject only removes an object from a to-many relationship, but does not delete the object from the store. To do so, you have to indeed use deleteObject - this is the desired behavior. Calling deleteObject will by default also set the corresponding relationships to nil (see https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html#//apple_ref/doc/uid/TP40001857-SW1).
I have an NSManagedObject that has a to-many relationship to another NSManagedObject.
During creation of the NSManagedObject I can use the generated accessors 'removeNotesObject' and the deletion works fine. I can create an object to add to the parent object, save the object, delete the object and then save again. When I fetch this parent object the object I created and deleted is still deleted.
However, after I add the object and then save it (but don't delete and save after) and then fetch it, I can't seem to delete the object that was previously created. I am using the generated accessors to try and remove the object, which appears to work but when I fetch it again the object hasn't been deleted.
(Note: Adding objects does work so it is not a problem with the saving)
To delete the object I retrieve the set of object and select the objects I want to delete. Then I remove the objects
NSSet *notes = summary.notes;
NSSet *oldNotes = [notes objectsPassingTest:^(id obj,BOOL *stop){
Note *oldNote = (Note *)obj;
BOOL sameRow = (oldNote.row == newNote.row);
BOOL sameColumn = (oldNote.column == newNote.column);
BOOL success = (sameRow && sameColumn);
return success;}];
[summary removeNotes:oldNotes];
I have tried making the relationship inverse to delete the objects which didn't delete them. I have also tried different delete rules (cascade and nullify) which again didn't work. Finally, I tried to remove each object separately and deleting each object from the context after I had removed it from the parent object which again unfortunately didn't work.
I assume the problem must be something to do with it being a fetched object. If anyone could help I would really appreciate it as I can't think of any other ways to test or solve this problem.
You need to do
NSManagedObjectContext * moc = .......;
[moc deleteObject:note]
edit: The core data generated accessors simply remove the object from the relationship, but do not delete the object permanently. This makes sense because you may have one NSManagedObject associated to multiple other NSManagedObjects via relationships.
edit: Deleting in the above mentioned fashion will invoke the deletion rules. I suggest you double check that they are setup correctly.
The reason the above code did not work is that == will not actually compare the NSNumber. Instead you need to call 'isEqualTo:'. I think before it was checking the address hence working before I saved it. What's more it was returning an object in the NSSet so appeared to be working. During debugging it wasn't clear what the object was but clearly wasn't the one I needed.