How can I validate a "does not match" type using CodeIgniter's Form Validation class?

Question

I want to ensure that a certain text field does not contain a specific value. Is there any way for me to do this using CI's Form Validation class or do I have to write my own extension for it?

Answer 1

I would extend the form validation class: http://codeigniter.com/user_guide/general/creating_libraries.html

Something like

<?
class MY_Form_validation extends CI_Form_validation {
  function __constuct() {
    parent::__constuct();
  }
  function isnt($str,$field){
    $this->CI->form_validation->set_message('isnt', "%s contains an invalid response");
    return $str!==$field;
  }
}
?>

Your validation rule would be something like

trim|alpha_numeric|isnt[invalid value]

Or, you can create a callback function instead of extending the class. The form validation section of the CI user guide has a relevant example: http://codeigniter.com/user_guide/libraries/form_validation.html#callbacks

Answer 2

I agree with Billiam that you should extend the Form_validation class

I find it is more likely that one would want to validate a white-list of possible string values rather than a black-list. For example, you know your 'shirt_size' field should only return the string values: 'xl','l','m','s'. My solution is to handle both cases.

I use these methods in MY_From_validation:

    /**
     * ENUM
     * The submitted string must match one of the values given
     *
     * usage:
     * enum[value_1, value_2, value_n]
     *
     * example (any value beside exactly 'ASC' or 'DESC' are invalid):
     * $rule['order_by'] = "required|enum[ASC,DESC]";
     * 
     * example of case-insenstive enum using strtolower as validation rule
     * $rule['favorite_corey'] = "required|strtolower|enum[feldman]";
     *
     * @access    public
     * @param     string $str the input to validate
     * @param     string $val a comma separated lists of values
     * @return    bool
     */
    function enum($str, $val='')
    {

        if (empty($val))
        {
        return FALSE;
        }

        $arr = explode(',', $val);
        $array = array();
        foreach($arr as $value)
        {
        $array[] = trim($value);
        }

        return (in_array(trim($str), $array)) ? TRUE : FALSE;
    }


    // --------------------------------------------------------------------

    /**
     * NOT ENUM
     * The submitted string must NOT match one of the values given
     *
     * usage:
     * enum[value_1, value_2, value_n]
     *
     * example (any input beside exactly 'feldman' or 'haim' are valid):
     * $rule['favorite_corey'] = "required|not_enum['feldman','haim']";
     *
     * @access   public
     * @param    string $str the input to validate
     * @param    string $val a comma separated lists of values
     * @return   bool
     */
    function not_enum($str, $val='')
    {
        return ($this->enum($str,$val) === TRUE)? FALSE : TRUE;
    }

Using Billiam's example, the validation rule not allow string 'invalid value' would be something like:

trim|alpha_numeric|not_enum[invalid value]

Answer 3

CodeIgniter's form validation class can call almost any declared PHP function in your rule set. So I would simply declare a function like so:

class yourController {
    function someFunction() {
        $this->form_validation->set_rules('the_field_you_want_to_check', 'The Field Name', 'trim|myvalfunc[not this value]|xss');
    }
}
function myvalfunc($formvalue, $notallowed) {
    $this->CI->form_validation->set_message('myvalfunc', "%s is not allowed");
    return $formvalue !== $nowallowed;
}

Answer 4

Actually, there's a fairly simple example given for this very question in the User Guide - http://codeigniter.com/user_guide/libraries/form_validation.html

Scroll down about halfway and you'll see the section "Callbacks: Your own Validation Functions". In the example it uses a check for the word "test" in the username field, and returns the custom error if the value is found.

In your controller, change the "username" rule to this:

$this->form_validation->set_rules('username', 'Username', 'callback_username_check');

Then add a new function called username_check to your controller:

function username_check($str)
{
    if ($str == 'test')
    {
        $this->form_validation->set_message('username_check', 'The %s field can not be the word "test"');
        return FALSE;
    }
    else
    {
        return TRUE;
    }
}

And Bob's your uncle...