Filter Array of Objects with NSPredicate based on NSInteger property in super class

Question

I've got the following setup:

@interface Item : NSObject {
    NSInteger *item_id;
    NSString *title;
    UIImage *item_icon;
}

@property (nonatomic, copy) NSString *title;
@property (nonatomic, assign) NSInteger *item_id;
@property (nonatomic, strong) UIImage *item_icon;

- (NSString *)path;

- (id)initWithDictionary:(NSDictionary *)dictionairy;

@end

And

#import <Foundation/Foundation.h>
#import "Item.h"

@interface Category : Item {

}

- (NSString *)path;

@end

I've got an array with Category instances (called 'categories') that I'd like to take a single item out based on it's item_id. Here is the code I use for that:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"item_id == %d", 1]; 
NSArray *filteredArray = [categories filteredArrayUsingPredicate:predicate];

This leads to the following error:

* Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ valueForUndefinedKey:]: this class is not key value coding-compliant for the key item_id.'

How can I fix this and what am I doing wrong? the properties are synthesized and I can acces and set the item_id property successfully on Category instances.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"item_id == 1"]; NSArray *filteredArray = [categories filteredArrayUsingPredicate:predicate]; — Manu, Apr 16 '13 at 11:26
@Manohar the 1, is not static, it's actually a NSInteger which is variable, I left the setting of the variable outside the example since it should not affect the question or the answer. Even though I gave your solution a try, and it gives the same error — Gidogeek, Apr 16 '13 at 11:34
Are you sure that you want the `item_id` property as a *pointer*? `NSInteger` is not an object, so perhaps you want just `NSInteger item_id`. — Martin R, Apr 16 '13 at 11:40
Thank you @MartinR that fixed it. Not sure why I added that as a pointer (3 years ago). Thanks! Make sure you add an answer so I can mark it as resolved. — Gidogeek, Apr 16 '13 at 11:45

score 4 · Accepted Answer · answered Apr 16 '13 at 11:47

4

You have declared the item_id property as a pointer. But NSInteger is a scalar type (32-bit or 64-bit integer), so you should declare it as

@property (nonatomic, assign) NSInteger item_id;

Remark: Starting with the LLVM 4.0 compiler (Xcode 4.4), both @synthesize and the instance variables are generated automatically.

answered Apr 16 '13 at 11:47

Martin R

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How to use title in place item_id, for me crashing if I am using any property? – Sanoj Kashyap Jul 02 '15 at 09:29
@Sandy: You better ask your own question to that you can provide all necessary information. – Martin R Jul 02 '15 at 09:32

score 3 · Answer 2 · answered Apr 16 '13 at 11:28

3

The first thing is that NSArray cannot contain primitive type of objects like 1, 2, 3. But, does contain object. So, when you create a predicate you should create it in the same way as such that it takes object. The above predicate should be reformed to something like this to work;

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"item_id == %@", @(1)];

answered Apr 16 '13 at 11:28

Sandeep

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I tried your solution, but it still gives me the exact same error. – Gidogeek Apr 16 '13 at 11:35

score 3 · Answer 3 · answered Apr 16 '13 at 11:38

3

NSString *str = [NSString stringWithFormat:@"%i",yourIntVariable];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"item_id == %@", str]; 
NSArray *filteredArray = [categories filteredArrayUsingPredicate:predicate];

answered Apr 16 '13 at 11:38

Manu

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This does not work. The issue is elsewhere: "this class is not key value coding-compliant for the key item_id." as mentioned in the question. The predicate looks correct to me as well, hence my confusion. When filtering on another items, which isn't inherited from the base class, it works perfectly. I believe the issue is in the KVC setup, not in the Predicate. But that's more a educated guess. – Gidogeek Apr 16 '13 at 11:41

Filter Array of Objects with NSPredicate based on NSInteger property in super class

3 Answers3

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