In an inventory system that we are working on each item has its record and each of those items has a reorder quantity. Similarly each of record has a calculation that establishes a quantity on hand.

I'd like to set up a portal that will display any record where the reorder level is greater than the on hand quantity. This is problematic because the on hand quantity is calculated by summerizing debits to inventory (through a relationship) and subtracting from additions to inventory (also through a relationship).

I'm thinking this is a pretty common problem. Any suggestions?

What if you were to not use calc fields for the on-hand inventory levels, and instead use a number field that's set by script when you pull from or add to inventory?

Then you could use a calc field in inventory that sets to "1" when your inventory level is less than the reorder level. That calc field can then be a stored calc and used as one of the keys for the portal. Actually, since you'd be setting your summary value by script, you could also set the key field by script. That would be even better.

The downside to this, of course, is more scripting.