I am trying to figure out how to calculate a running total using core
data. I have created an entity called Transactions that have the
following properties.
Transactions
amount
balance
I am trying to calculate the balance by adding up the amount of all
the previous balances. I have subclased NSManagedObject and
overridden awakeFromFetch. Here is the code I have so far.
- (void)awakeFromFetch
{
[super awakeFromFetch];
double amount = [[self valueForKey:@"amount"] doubleValue];
[self setValue:[NSNumber numberWithFloat:amount]
forKey:@"balance"];
}
This routine only copies the amount to the balance property. I am
thinking that I have to Query all of the previous transactions and
calculate their totals. I know how to create a NSFetchRequest on a
transaction object but I am unsure on how to create the NSPredicate
object to extract all the transactions that were created prior to the
current transaction. Thanks for any help you can provide.
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