Update a Core Data record in iOS application

Question

I've just read some tutorials and decide to add Core Data storage to my project. Then I implement "create" and "read" methods. It works OK. But then I encountered a problem with "update" method.

- (void)updateForecastPlace:(NSString *)placeString
{
    NSManagedObjectContext *context = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:ENTITY_NAME inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    NSError *error = nil;
    NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
    WFForecast *forecastToUpdate;

    for (WFForecast *forecast in fetchedObjects)
    {

        if ([[forecastToUpdate timestamp] compare:[forecast timestamp]] == NSOrderedAscending)
        {
            forecastToUpdate = forecast;
        }

    }

    [forecastToUpdate setPlace:placeString];
    error = nil;

    if ([context save:&error])
    {
        NSLog(@"Forecast information was updated!");
    }
    else
    {
        NSLog(@"The forecast information was not updated: %@", [error userInfo]);
    }

}

I'm fetching objects from context. (It's OK)

Then choose one to update.

Setup new value to its property( [forecastToUpdate setPlace:placeString];)

Then save the context. ( [context save:&error] )

It seems like it works (it's rise no errors and send success massage to console log). But when I read this object it appears to be non-updated. I read a lot of stuff on this problem but didn't figure out how to fix it. Any suggestions, please?

UPDATE: I check the value of my updated object property place

[forecastToUpdate setPlace:placeString];
NSLog(@"---arg value %@", placeString);
NSLog(@"---updated value %@", [forecastToUpdate place]);

and got the output like:

---arg value Sydney, Australia
---updated value (null)

Any idea what caused such mistake?

your code seems ok, be sure you read the right object. also check if you have the right value of 'forecastToUpdate.place' just before saving the context — Idali, Sep 15 '15 at 00:49
Idali, thanks. Your comment pushed me a little forward in my solution. (Check the update) — nadein, Sep 15 '15 at 07:31

score 0 · Accepted Answer · answered Sep 15 '15 at 07:49

Unfortunately the problem was in my inattentiveness :( I forgot to assign fetched object with my objectToUpdate pointer before compare values and do other stuff.

 WFForecast *lastestForecast = fetchedObjects[0]; // <- missed this row

for (WFForecast *forecast in fetchedObjects)
{
    NSLog(@"%@", [forecast place]);
    if ([[lastestForecast timestamp] compare:[forecast timestamp]] == NSOrderedAscending)
    {
        lastestForecast = forecast;
    }

}

Update a Core Data record in iOS application

1 Answers1