REGEX Validation Rule error on blank field

Question

I am trying to create a validation rule for a text field to only allow letters and a few special characters to be saved in the field. The special characters are " - ", " . "," - ".

This is the rule I have so far.

not(REGEX( Test_Validation_Rule_Field__c , "[a-zA-Z0-9- \.\,\- ]+"))

My issue currently that is impeding me from finishing the rest is now the field will not save when I try to clear the field. It makes it required after initially saving a field, which isn't the the greatest UX.

Answer 1

Validation rules fire when the result of the formula is true. So you'll need to add something to your validation rule to allow blank as a valid value.

This could be as simple as changing the + in your regex, which denotes "1 or more of these things",
to *, which denotes "any number, including 0 of these things"

While that should be perfectly understandable by people with a working knowledge of regex, it wouldn't be obvious to laypeople. An alternate approach would be to add in a NOT(ISBLANK(<your field here>)) and AND() those two conditions together.

e.g.

/* Only returns true if all of the conditions inside are true */
/* So the field being blank is enough to get you out of the validation */
/* Blank check first to take advantage of short-circuit evaluation */
AND(
    NOT(ISBLANK(<your field here>)),
    <existing statement with the regex>
)

Having the blank check be explicit should make it easier for others to reason about (if that is a concern).

Answer 2

You can use an "if" statement in your validation rule, to evaluate the rule only if the field is not blank

as such:

IF(NOT(ISBLANK(your_field__c)), (your regex expression), false)

this will make sure, your validation rule is trigged only when the field is not blank.