Database Reference
In-Depth Information
But sometimes “blank” isn't the right value. When you create a new invoice, its Total Due
value is “blank” (there's no data in the field), but it should be zero dollars and zero cents, or
$0.00. First, turn off the “Do not evaluate if all referenced fields are empty” option for In-
voices::Total Due. Then change that field's calculation to:
0 + Sum ( Line Items::Extended Price )
The calculation's result isn't changed by the addition of the constant value “0,” but there's
now a value in the fields that'll trigger evaluation of the calculation, even when the invoice
has no related items ( Figure 9-8 ).
TIP
Still don't see that zero? Switch to Layout mode, select the Total Due field and then take a look at
the Data Formatting options in the Data tab of the Inspector. Make sure the “Do not display number
if zero” checkbox is turned off.
Auto-Enter Calculations
Back on Container , you learned about most of the auto-enter field options. Now that you
know about calculations, it's time to learn how to combine the power of the calculation en-
gine (accuracy and efficiency) with the ability to override a calculated value using auto-enter
calculations. Calculation fields are fantastic—they save time and ensure error-free results.
But they have one serious limitation: You can't click into a calculation field and change its
value . Of course, you can adjust the calculation itself, or the data in the fields the calculation
depends on, but sometimes you need to be able to override a field's calculated value on a
record-by-record basis.
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