Overriding setters with arc and dynamic properties

Question

I need to do some additional stuff in a setter method. But I get an infinite loop when doing so:

I've got a core data object

@interface Transaction : NSManagedObject 
@property (nonatomic, retain) NSDate * date;
@end

@implementation Transaction
@dynamic date;

-(void)setDate:(NSDate *)date
{
    self.date = date;
    //additional stuff omitted
}

So, in that case I get an infinite loop. Okay so I searched on the net and modified my code in the following way and for every version I get compiler errors

Version 1:

@interface Transaction : NSManagedObject 
@property (nonatomic, retain) NSDate * date;
@end

@implementation Transaction
@dynamic date;

-(void)setDate:(NSDate *)date
{
    self->date = date; //Error: Property 'date' found on object 'Transaction *'; did you mean to access it with the "." operator?
    //additional stuff omitted
}

Version 2:

@interface Transaction : NSManagedObject 
@property (nonatomic, retain) NSDate * date;
@end

@implementation Transaction
@dynamic date = _date; //Error: Expected ';' after @dynamic

-(void)setDate:(NSDate *)date
{
    _date = date; 
    //additional stuff omitted
}

Now, I'm asking myself how to do this?

score 5 · Accepted Answer · answered Dec 18 '11 at 00:21

5

The solution to my problem:

@interface Transaction : NSManagedObject 
@property (nonatomic, retain) NSDate * date;
@end

@implementation Transaction
@dynamic date;

-(void)setDate:(NSDate *)date
{
    [self setPrimitiveValue:date forKey:@"date"];
    //additional stuff omitted
}

answered Dec 18 '11 at 00:21

toom

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2

Call willChangeValueForKey before and didChangeValueForKey after to keep KVO. – brodney Jan 28 '14 at 14:54

score 2 · Answer 2 · edited May 23 '17 at 10:28

Is "date" backed by a corresponding attribute in Core Data?

If so, please take a look at Custom setter methods in Core-Data

If not, and you don't need to persist "date", your code should be the following:

@interface Transaction : NSManagedObject 
@property (nonatomic, retain) NSDate * date;
@end

@implementation Transaction
@synthesize date = _date;

-(void)setDate:(NSDate *)date
{
    _date = date; 
    //additional stuff omitted
}

malhal · Answer 3 · 2018-03-28T09:00:49.737

Here is the Apple way for overriding NSManagedObject properties without breaking KVO, in your .m:

@interface Transaction (DynamicAccessors)
- (void)managedObjectOriginal_setDate:(NSDate *)date;
@end

@implementation Transaction
@dynamic date;

- (void)setDate:(NSDate *)date
{
    [self managedObjectOriginal_setDate:(NSString *)date;
    // your custom code
}

As seen at bottom of this page What's New in Core Data in macOS 10.12, iOS 10.0, tvOS 10.0, and watchOS 3.0

Overriding setters with arc and dynamic properties

3 Answers3

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