Forum OpenACS Q&A: validation

I need to validate a variable in ad_form, but I'm having troubles with it because the validation must be in an if statement, right now I'm using -extend but it doesn't work.
  I'll apreciate any help

The code goes like this:

if { *condition* } {
ad_form -extend -name form_name -validate {
  {var_name
  { *condition* }
    "Message"
  }
}

the problem is that even when the condition of the if statement is true, the validation doesnt work.

Thanks for your help.

Here's a method I use that utilizes a procedure to validate:

In your form processing page code:

} -validate {
    {value {[valid_value err $value]} $err }
}

"err" is a var parameter that is set by procedure validate_value. On error you set it with the appropriate error message.

And the procedure looks something like:

ad_proc -public valid_value {
    err
    value
} {
    Validates value.
    @return 1 if valid, $err == "".  0 if invalid, $err == descriptive string.
    @param err name of var parameter, in caller's scope, that receives error description.
    @param value the value to be validated.
} {
    upvar 1 $err lerr
    if {[string length $value] < 3} {
	set lerr "\"value\" must be a string containing three or more characters"
	return 0
    }
    set lerr ""
    return 1
}

This might seem like overkill for this simple example, but more complex checks and/or recovery can be performed in a more complex situation.

/R