Question

I am using Core Data to save some strings. I have the following class called Results

Results.h

#import <CoreData/CoreData.h>

@interface Results : NSManagedObject

@property(nonatomic, retain) NSString *lessondate;
@property(nonatomic, retain) NSString *lesson;
@property(nonatomic, retain) NSString *location;
@property(nonatomic, retain) NSString *start;
@property(nonatomic, retain) NSString *end;

@end

Results.m

#import "Results.h"

@implementation Results

@dynamic lessondate;
@dynamic lesson;
@dynamic location;
@dynamic start;
@dynamic end;

@end

The following is my code to perform the save:

-(void)saveLesson{

Results *result = (Results *)[NSEntityDescription insertNewObjectForEntityForName:@"Diary" inManagedObjectContext:managedObjectContext];

result.lessondate = calendarDateString;
result.lesson = [NSString stringWithFormat:@"%@", lessonText.text];
result.location = [NSString stringWithFormat:@"%@", locationTest.text];
result.start = [NSString stringWithFormat:@"%@", startTimeText.text];
result.end = [NSString stringWithFormat:@"%@", endTimeText.text];
NSError *error;


// here's where the actual save happens, and if it doesn't we print something out to the console
if (![managedObjectContext save:&error])
{
    NSLog(@"Problem saving: %@", [error localizedDescription]);
}


[self dismissViewControllerAnimated:YES completion:nil];

}

But when I try to save the data in the app, the app crashed and shows these errors

2013-02-18 11:46:25.705 After managedObjectContext: <NSManagedObjectContext: 0x1f892480>

2013-02-18 11:46:33.762 -[NSManagedObject setLesson:]: unrecognized selector sent to instance 0x1f80b380

2013-02-18 11:46:33.764  *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSManagedObject setLesson:]: unrecognized selector sent to instance 0x1f80b380'

Can someone please tell me why this is crashing? The exact same code is in another app and that works fine.

Answer 1

You are creating an entity different from what you expect.

You are calling

[NSEntityDescription insertNewObjectForEntityForName:@"Diary"
                              inManagedObjectContext:managedObjectContext];

which creates entity Diary. Put @"Results" as a first argument for the method.

While you are assigning the created Diary entity into a Results object, it is only a syntactic sugar—the real object underneath is what you have passed as an entity name.
Diary object doesn’t have the lesson property, and you get the exception.