Core Data : Updating array.

Question

I have a Core Data model entity NoteObject that has a transformable type arrayOfTags. In the NoteObject.h file, which is a subclass of NSManagedObject, the arrayOfTags is declared as:

NSMutableArray *arrayOfTags;
@property (nonatomic, retain) NSMutableArray *arrayOfTags;
//.m
@dynamic arrayOfTags;

The issue is that changes that are made to this array are not saved. Someone suggested the following as the solution:

If there are mutable and immutable versions of a class you use to represent a property—such as NSArray and NSMutableArray—you should typically declare the return value of the get accessor as an immutable object even if internally the model uses a mutable object.

However I'm not exactly sure what that means. How would I follow those instructions for my case?

By adding to it. This is the original question I asked: stackoverflow.com/questions/9556834/… — Snowman
– Snowman, Commented Mar 5, 2012 at 21:22
From my understanding of this is that You would copy the NSMutableArray into a NSArray and return the NSArray for use. — Seb
– Seb, Commented Mar 5, 2012 at 21:25

Felix · Accepted Answer · 2012-03-05 21:37:07Z

1

Even of you've found a workaround in the meantime try this:

[noteObject willChangeValueForKey:@"arrayOfTags"];

// make changes to noteObject.arrayOfTags

[noteObject didChangeValueForKey:@"arrayOfTags"];

answered Mar 5, 2012 at 21:37

Felix

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2 Comments

Snowman Over a year ago

Yes this actually worked too. Which is better, your suggestion, or the [noteObject setArrayOfTags:noteObject.arrayOfTags]?

user207616 Over a year ago

yep this one is better and which I have used in my projects. As far as I can remember I have copied from Apple sample code. (could be the books example but not sure anyway). EDIT: its 'better' because it doesn't rely on other conditions. Its like with bindings on the Mac, just tells Cocoa that changes were made, and please update all related objects.

Seb · Accepted Answer · 2012-03-05 21:42:17Z

1

Implementing accessor functions for Core Data varies with your relationship model. This document should help you get started. Most likely you will be using this setup for your getter:

- (NSArray*)data
{
    [self willAccessValueForKey:@"data"];
    NSArray* array = [[NSArray alloc] initWithArray:arrayOfTags copyItems:YES];
    [self didAccessValueForKey:@"data"];
    return array;
}

Please note that the above snippet is just an example and will have to be modified for your use.

answered Mar 5, 2012 at 21:42

Seb

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