How can I test if an attribute of a CoreData object is null?

Question

I want to test if an NSNumber attribute of a NSManageObject Subclass has been set or not. Note, that the attribute is of NSNumber / Integer16 I have tried several approaches but none worked (these below always evaluate to false):

// Note: patient.zyklus_laenge is of NSNumber (Integer16)
// does not work
id value = patient.zyklus_laenge;
if (value == [NSNull null]) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if (!patient.zyklus_laenge) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if ([patient.zyklus_laenge isEqual:nil]) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if (patient.zyklus_laenge == nil) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}

Can anyone enlighten me and explain me why these are not working?

What does `patient.zyklus_laenge` return in command line, when it's nil? — Valentin Shamardin, Oct 28 '14 at 15:26
Tried already, see the last if-else, to no avail. NSLog always shows: `patient.zyklus_laenge: (null)` but the `else` branch never executes — mrd, Oct 28 '14 at 15:29
this should help http://stackoverflow.com/questions/1188413/storing-optional-nsnumber-in-core-data — Flexicoder, Oct 28 '14 at 15:36
No, this does not help in my case. Because: I am migrating from one model version to a newer. patient objects which were created before migration don't have the attribute yet. Once they migrate, the old patient objects will have `zyklus_laenge` attribute, but not set. Newly created patient objects do have the value set on creation. — mrd, Oct 28 '14 at 15:49
Try checking if ([patient.zyklus_laenge intValue] == 0). This should return true if the value was not set before. — Mike Taverne, Oct 28 '14 at 16:29

ekiyanov · Answer 1 · 2014-10-28T20:44:27.653

0

id value = patient.zyklus_laenge;
if (value == [NSNull class])

to

id value = patient.zyklus_laenge;
if ([value isKindOfClass:[NSNull class]])

edited Oct 28 '14 at 20:44

answered Oct 28 '14 at 15:53

ekiyanov

441
3
19

This works, but it gives me a compiler warning: Incompatible pointer types. I found a different solution, see below – mrd Oct 28 '14 at 16:08
Maybe he meant `[NSNull class]` ? – Mundi Oct 28 '14 at 16:19
No, i tried that, because it seemed logical to me. But `[NSNull class]` did not work for me – mrd Oct 28 '14 at 23:07

score 0 · Answer 2 · answered Oct 28 '14 at 16:12

The solution is to set the attribute in core data as required with a default value and to test with this code:

if (!patient.zyklus_laenge) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}

score 0 · Answer 3 · answered Oct 28 '14 at 17:33

If you have a default value set for the attribute, it will be that default value, which is normally 0, not null.

If so, you can check the following:

if (patient.zyklus_laenge.intValue == 0)

Otherwise, this null check can be used:

if (patient.zyklus_laenge != nil)

How can I test if an attribute of a CoreData object is null?

3 Answers3

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