Core Data Issue - Unable to store NSNumber - objective-c

Question

I am trying to use Core Data in my application. I want to store an attribute "totalKM".
to store my attribute I use these lines:
Model *event = (Model *)[NSEntityDescription insertNewObjectForEntityForName:#"Model" inManagedObjectContext:managedObjectContext];
int number = 4;
[event setTotalKM:[NSNumber numberWithDouble:number]];
to read my attribute I use these:
Model *event = (Model *)[NSEntityDescription insertNewObjectForEntityForName:#"Model" inManagedObjectContext:managedObjectContext];
NSNumber *number = [event totalKM];
My attribute "totalKM" is always default value, O. And I have no exception. Am i missing something?
Thanks.

Answer 1

insertNewObjectForEntityForNamethis method use to put model to context.
this is a new object.
the right way is:
Set new one
Model *event = (Model *)[NSEntityDescription insertNewObjectForEntityForName:#"Model" inManagedObjectContext:managedObjectContext];
int number = 4;
[event setTotalKM:[NSNumber numberWithDouble:number]];
//save change if need
NSError *error = nil;
if (![self.manageObjectContext save:&error]) {
NIDERROR(#"save managedContext error :%#",error);
}
fetch object progress
When you need to get a model form coredate.u need 2 fetch use fetch
like this dome
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];
[fetchRequest setEntity:[NSEntityDescription entityForName:#"Board"
inManagedObjectContext:self.manageObjectContext]];
//set fetch conditions
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"board_id == %#", aBoardID];
[fetchRequest setPredicate:predicate];
NSError *error = nil;
NSArray *results = [self.manageObjectContext executeFetchRequest:fetchRequest error:&error];
if (error) {
NIDERROR(#"fetch board error.\n board id: %# \n error:%#", aBoardID, error);
return nil;
}
Model *model = results[0];
NSLog(#"%#",model.totalKM)