CFPARAM for Simple String Validation

May 29, 2007

With the addition of a dozen new type values for the cfparam tag in ColdFusion 7, it has become a handy tool for validation.

I have a little trick for those of you who are using earlier versions of ColdFusion that don't support the new types for validation. One of the type attribute values that has been supported for quite some time is the variablename type.

This is handy for validating that a simple one word string has been been passed. According to the docs a varaiblename starts with a letter, underscore (_), or Unicode currency symbol, and contains letters, numbers, underscores, periods, and Unicode currency symbols, only. This means that this type has safety from cross site scripting attacks, and sql injection attacks.

The code may look something like this:

<cfparam name="url.action" type="variablename" default="edit">

If you have ColdFusion 7 you can one up this and limit the values passed in with a simple regular expression:

<cfparam name="url.action" default="edit" type="regex" pattern="(new|edit|delete)">

The regex example only allows the string's new, edit, or delete to be passed in. That's a solid way to validate our input strings.

Wouldn't it be nice however if you could do something like this:

<cfparam name="url.action" type="finite" list="new,edit,delete">

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I find types to be of little use for validation, since the first error found throws an exception that gives you helpful information like the following: Invalid parameter type. The value cannot be converted to a numeric because it is not a simple value. Simple values are booleans, numbers, strings, and date-time values. "The value"? Great. Now I know is that one of my numeric form fields threw an error, but not which one... guess I can tell the user to double-check ALL of his entries.

Foundeo Inc.