On Jun 18, 2008, at 13:04, Ben Trumbull wrote:
*Amount* is an calculated field and it depends on the previous
transactions.
I don't know how to do it! It is not a value I can save on
database, for
example, because it changes all the time (I guess I have to mark the
transient field at Core Data).
As someone else mentioned, you probably want to move "amount" over
to Account as "balance". You can make it transient.
Given that the OP seemed to want to display cumulative balances with
each displayed transaction (like a Quicken register does), a single
account balance property doesn't really help.
And the right approach (whatever it is) is a little bit subtle, I
think. If there are multiple transactions with the same sort key (the
same date, in the OP's example), or the transactions might be listed
in various orders, you'd have to accumulate the balance based on the
actual displayed order, so it's unlikely that it could be kept in the
data model (e.g. as a Core Data property) unless you added transient
sets of report items separately from the set of transactions. In a
way, the balance is a transient property of the "V" rather than the "M".
This is a bit OT, I guess, but it's interesting to notice that Cocoa
doesn't seem to have any standard coding patterns that would deal with
this simple-seeming case.
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