$this->validation->set_rules(array( 'username' => 'trim|required|callback_users_model->is_unique[username]', 'password' => 'trim|required|matches[confirm]', )); 

 /**  * Validation callback  **/ function is_unique($value, $field) { $this->validation->set_message('users_model->is_unique', "The %s {$value} is not available. Try a different username"); return (bool)(!$this->findBy("{$field} = '{$value}'")); } 

<?php if (!defined('BASEPATH')) exit('No direct script access allowed'); /**  * MY_Validation extension  *  * Allows callback functions into Module or Models  *   * Version 0.3 (c) Wiredesignz 2008-04-24  */ class MY_Validation extends CI_Validation { function get_fields() { return $this->_fields; } /**  * Run the Validator  *  * This function does all the work.  *  * @access public  * @return bool  */ function run(&$parent) { // Do we even have any data to process? Hmm?  if (count($_POST) == 0 OR count($this->_rules) == 0) { return FALSE; } // Load the language file containing error messages $parent->load->language('validation'); // Cycle through the rules and test for errors foreach ($this->_rules as $field => $rules) { //Explode out the rules! $ex = explode('|', $rules); // Is the field required? If not, if the field is blank we'll move on to the next test if ( ! in_array('required', $ex, TRUE)) { if ( ! isset($_POST[$field]) OR $_POST[$field] == '') { continue; } } /*  * Are we dealing with an "isset" rule?  *  * Before going further, we'll see if one of the rules  * is to check whether the item is set (typically this  * applies only to checkboxes). If so, we'll  * test for it here since there's not reason to go  * further  */ if ( ! isset($_POST[$field])) { if (in_array('isset', $ex, TRUE) OR in_array('required', $ex)) { if ( ! isset($this->_error_messages['isset'])) { if (FALSE === ($line = $parent->lang->line('isset'))) { $line = 'The field was not set'; } } else { $line = $this->_error_messages['isset']; } // Build the error message $mfield = ( ! isset($this->_fields[$field])) ? $field : $this->_fields[$field]; $message = sprintf($line, $mfield); // Set the error variable. Example: $this->username_error $error = $field.'_error'; $this->$error = $this->_error_prefix.$message.$this->_error_suffix; $this->_error_array[] = $message; } continue; } /*  * Set the current field  *  * The various prepping functions need to know the  * current field name so they can do this:  *  * $_POST[$this->_current_field] == 'bla bla';  */ $this->_current_field = $field; // Cycle through the rules! foreach ($ex As $rule) { // Is the rule a callback?  $callback = FALSE; if (substr($rule, 0, 9) == 'callback_') { $rule = substr($rule, 9); $callback = TRUE; } // Strip the parameter (if exists) from the rule // Rules can contain a parameter: max_length[5] $param = FALSE; if (preg_match("/(.*?)\[(.*?)\]/", $rule, $match)) { $rule = $match[1]; $param = $match[2]; } // Call the function that corresponds to the rule if ($callback === TRUE) { /* Allows callbacks into Models */ if (list($class, $method) = split('->', $rule)) { if ( ! method_exists($parent->$class, $method)) { continue; } $result = $parent->$class->$method($_POST[$field], $param); } else { if ( ! method_exists($parent, $rule)) { continue; } $result = $parent->$rule($_POST[$field], $param); } /* Original code continues */ // If the field isn't required and we just processed a callback we'll move on... if ( ! in_array('required', $ex, TRUE) AND $result !== FALSE) { continue 2; } } else { if ( ! method_exists($this, $rule)) { /*  * Run the native PHP function if called for  *  * If our own wrapper function doesn't exist we see  * if a native PHP function does. Users can use  * any native PHP function call that has one param.  */ if (function_exists($rule)) { $_POST[$field] = $rule($_POST[$field]); $this->$field = $_POST[$field]; } continue; } $result = $this->$rule($_POST[$field], $param); } // Did the rule test negatively? If so, grab the error. if ($result === FALSE) { if ( ! isset($this->_error_messages[$rule])) { if (FALSE === ($line = $parent->lang->line($rule))) { $line = 'Unable to access an error message corresponding to your field name.'; } } else { $line = $this->_error_messages[$rule]; } // Build the error message $mfield = ( ! isset($this->_fields[$field])) ? $field : $this->_fields[$field]; $mparam = ( ! isset($this->_fields[$param])) ? $param : $this->_fields[$param]; $message = sprintf($line, $mfield, $mparam); // Set the error variable. Example: $this->username_error $error = $field.'_error'; $this->$error = $this->_error_prefix.$message.$this->_error_suffix; // Add the error to the error array $this->_error_array[] = $message; continue 2; } } } $total_errors = count($this->_error_array); /*  * Recompile the class variables  *  * If any prepping functions were called the $_POST data  * might now be different then the corresponding class  * variables so we'll set them anew.  */ if ($total_errors > 0) { $this->_safe_form_data = TRUE; } $this->set_fields(); // Did we end up with any errors?  if ($total_errors == 0) { return TRUE; } // Generate the error string foreach ($this->_error_array as $val) { $this->error_string .= $this->_error_prefix.$val.$this->_error_suffix."\n"; } return FALSE; } }