FileMaker Pro 9: The Missing Manual

Validate Data Entry with a Calculation

In Chapter 3 you were introduced to several ways to validate data entered into a field. But what if the Validation tab in the Field Options dialog box doesn’t have a checkbox to meet your needs? For example, you may want to use validation on the Zip Code field in the Customers table. A valid Zip code has either five characters or 10 characters (in other words, it can look like this: 90210, or this: 90210-1100). The closest validation option you’ll find is “Maximum number of characters”—close, but not right.

This situation is just the kind where the “Validate by calculation” option comes in handy. Your job is to create a calculation with a Boolean result. It should return True when the data is valid, and False otherwise. Here’s how it works:

1. View the field definitions for the Customers table (In File → Manage Database). Select the Zip Code field, and then click Options.

   The Field Options dialog box pops up.

2. Click the Validation tab, and turn on “Validate by calculation.”

   The Specify Calculation window appears, ready for you to enter your validation calculation.

3. From the View pop-up menu, choose “Text functions.”

   The function list updates to show just the text functions.

4. In the function list, double-click “Length (text).”

   The function appears in the calculation box. Notice that “text” is already highlighted, ready to be replaced. The length function returns the length of a text value. You use it here to see how many characters are in the Zip Code ...