I have a need to sort a CoreData table on one attribute in a table that needs
to be derived from a calculation. I read about "Non-Standard Persistent
Attributes" and did google and the only way I found to make it work is
according to the following:
So, suppose I have an entity "Entity":
@implementation Entity
@dynamic attribute1;
@dynamic attribute2;
@synthesize positive;
@synthesize negative;
@dynamic net_count;
- (void)setPositive:(NSNumber *)newPositive
{
[self willChangeValueForKey:@"positive"];
positive = newPositive;
[self didChangeValueForKey:@"positive"];
[self willChangeValueForKey:@"net_count"];
self.net_count = [NSNumber numberWithInteger:self.positive.integerValue
- self.negative.integerValue];
[self didChangeValueForKey:@"net_count"];
}
- (void)setNegative:(NSNumber *)newNegative
{
[self willChangeValueForKey:@"negative"];
negative = newNegative;
[self didChangeValueForKey:@"negative"];
[self willChangeValueForKey:@"net_count"];
self.net_count = [NSNumber numberWithInteger:self.
positive.integerValue - self.negative.integerValue];
[self didChangeValueForKey:@"net_count"];
}
@end
That seems to work. Records appear in the right order.
Is there anything that I'm doing wrong with the above?
I initially tried to provide a dynamic value when net_count was called, e.g.
implementing an accessor like:
- (NSNumber *)net_count
{
return [NSNumber numberWithInteger:self.positive.integerValue -
self.negative.integerValue];
}
But the records were not ordered properly.
-Laurent.
--
Laurent Daudelin
AIM/iChat/Skype:LaurentDaudelin
http://www.nemesys-soft.com/
Logiciels Nemesys Software
laur...@nemesys-soft.com
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