Handling invalid data

How you handle invalid data depends on the validation type. This section describes validation error-handling rules and considerations. For detailed information on error handling in ColdFusion, including invalid data handling, see Handling Errors.

For onBlur, onSubmit, or onServer validation, you can use the cfinput or cftextarea tag's message attribute to specify a text-only error message to display. Otherwise, ColdFusion MX uses a default message that includes the name of the form field that was invalid. (For OnServer validation, you can customize this message, as described in Handling form field validation errors.) The following example displays an error message when the user enters an invalid e-mail address:
```
	E-mail: <cfinput type="text" size="25" name="email"
		validate="email" message="You must enter a valid e-mail address.">
```
For hidden form validation, you can specify a text-only error message in the hidden field's value attribute. Otherwise, ColdFusion MX uses a default message that includes the name of the form field that was invalid. (You can customize this message, as described in Handling form field validation errors.) The following cfinput tag, for example, uses a hidden field validation to display an error message if the user enters an invalid address. (It uses onServer validation to display a different error message if the user fails to enter a number.)
```
Telephone: <cfinput type="text" size="20" name="telephone"
	validateat="onServer" required="Yes" 
	message="You must enter a telephone number">
	<cfinput type="hidden" name="telephone_cfformtelephone" 
	value="The number you entered is not in the correct format.<br>Use a
	number such as (617) 555-1212, 617-555-1212, or 617-555-1212 x12345">
```
For HTML and XML format forms (using ColdFusion MX skins), most ColdFusion form tags have an onError attribute that lets you specify a Javascript function to run if an onSubmit error occurs.
For the IsValid function, you write separate code paths to handle valid and invalid data. The following example shows a simplified case that displays an error message if the user entered an invalid e-mail address, or a different message if the address is valid:
```
<cfif IsValid("email", custEmail)>
	Thank you for entering a valid address.
	
<cfelse>
	You must enter a valid e-mail address.<br>
	Click the Back button and try again.
</cfif> 
```
For cfparam and cfargument tags, you use standard ColdFusion MX error-handling techniques. You can include the tag in a try block and use a catch block to handle the error, or you can use a custom error-handling page. The following example form action page code uses a custom error page, expresserr.cfm, to handle the error that the cfparam tag generates if a user submits a form with an invalid e-mail address:
```
<cferror type="EXCEPTION" exception="expression" template="expresserr.cfm">
<cfif IsDefined("form.fieldnames")>
	<cfparam name="form.custEmail" type="email">
	
</cfif>
```

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