Core Data: Updating Data Corresponding to a Key

How can I update data corresponding to any开发者_如何学Go key in Core Data?

Thanks

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For updating any entry in core data you need first fetch that entry then make object for that entity then set all properties of that see this code,

NSMutableArray *fetchResults;
    NSString *entityName=@"YourEntity";
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:globalManagedObjectContext];
    [fetchRequest setEntity:entity];

    fetchResults = [NSMutableArray arrayWithArray:[globalManagedObjectContext executeFetchRequest:fetchRequest error:nil]];
    [fetchRequest release];

[fetchResults filterUsingPredicate:[NSPredicate predicateWithFormat:@"id==%@",comparing_key]];
    objEntity=[fetchResults objectAtIndex:0];

    objEntity.pro1=@"some value";
    objEntity.pro2=@"some value";

    if (![globalManagedObjectContext save:nil]) 
        NSLog(@"Error in storing to database");