Extend EE_Loader (or CI_Loader) in ExpressionEngine

Question

I want to extend the EE_Loader class in ExpressionEngine 2, without hacking at core EE (or CI) code.

I tried to follow the advice from Simon Emms' blog which would be a clean way to extend CI_Loader, and follows the standard convention for extending a CI class.

I've tried adding a EE_Loader.php file within codeigniter/system/core/, which is where CI_Loader (in file Loader.php) lives. My subclass_prefix is 'EE_' because I'm using ExpressionEngine so I'm confident with the filename being used, but it's not reading in the new file.

Has anyone been successful in extending ExpressionEngine's EE_Loader class? Any pointers would be appreciated.

To provide some background, I have written a PHP Session handler which writes to MySQL, using Active Record to form my queries. It will be used in a web cluster so I need to share sessions. I have considered using a NFS file, memcached, redis and MySQL solutions. MySQL is already in use, will perform well and provides a centralised store.

After reading the session data from the DB, I make another call to write to the DB, but I get a "deprecated" warning:

A PHP Error was encountered
Severity: 8192

Message: mysql_escape_string(): This function is deprecated; use mysql_real_escape_string() instead.

Filename: mysql/mysql_driver.php
Line Number: 319

I also get the same message when I use the mysqli driver.

It's happening because $this->conn_id becomes false between 2 queries. I don't know why.

Answer 1

For future reference, I created a new set of DB drivers (eemysqli) which are a renamed (filenames and class names) but otherwise exact copy of codeigniter/system/database/drivers/mysqli/*. I then applied the following edit to eemysqli_driver.php:

--- drivers/mysqli/mysqli_driver.php    2012-11-26 15:19:21.000000000 +0000
+++ drivers/eemysqli/tcmysqli_driver.php        2012-12-11 19:45:45.375905181 +0000
@@ -28,7 +37,7 @@
  * @author             ExpressionEngine Dev Team
  * @link               http://codeigniter.com/user_guide/database/
  */
-class CI_DB_mysqli_driver extends CI_DB {
+class CI_DB_eemysqli_driver extends CI_DB {

        var $dbdriver = 'mysqli';

@@ -278,6 +287,8 @@
     /**
      * Escape String
      *
+     * I (AD) have amended this function to fix a known bug which is fixed in CI3.
+     *
      * @access      public
      * @param       string
      * @param       bool    whether or not the string will be used in a LIKE condition
@@ -295,18 +306,7 @@
                        return $str;
                }

-               if (function_exists('mysqli_real_escape_string') AND is_object($this->conn_id))
-               {
-                       $str = mysqli_real_escape_string($this->conn_id, $str);
-               }
-               elseif (function_exists('mysql_escape_string'))
-               {
-                       $str = mysql_escape_string($str);
-               }
-               else
-               {
-                       $str = addslashes($str);
-               }
+        $str = is_resource($this->conn_id) ? mysql_real_escape_string($str, $this->conn_id) : addslashes($str);

                // escape LIKE condition wildcards
                if ($like === TRUE)

It's a bit of a nonsense, but I can rest easy knowing I haven't hacked core EE/CI files.

Answer 2

About a year ago i made a proof of concept to integrate DataMapper ORM into ExpressionEngine.
DataMapper is a database abstraction library for CodeIgniter, that does exactly that, replace the load_class function.

It turned out that the version of CodeIgniter that ships with ExpressionEngine, does not do the check if function_exist() before loading most or any of the core functions. It took only a very small modification to the core to be able to override the load_class function. It boils down to wrapping the load_class function in a if not function_exists conditional.

# 1. file: /system/codeigniter/system/core/Common.php
if ( ! function_exists('load_class'))
{
    function &load_class($class, $directory = 'libraries', $prefix = 'CI_')
    {
    ...
    }
}

This allows us to load our own bootstrap first from the main index.php file, just before the core system bootstrap would have been loaded.

# 2. file: /index.php at the, just before loading the bootstrap file
require_once APPPATH.'third_party/datamapper/bootstrap.php';

NOTES

1. the code can be found on https://github.com/GDmac/EE_DataMapper/

2. The naming can be a bit confusing.
   A). The CodeIgniter ActiveRecord class actually is a QueryBuilder, and in CodeIgniter 3 it correctly has been renamed to QueryBuilder.
   B). Datamapper ORM ( http://datamapper.wanwizard.eu ) actually
   follows the ActiveRecord design pattern.
   C). DataMapping is another design pattern, which abstracts the database away from the rest of the code

3. general tip: Avoid hacking core with lots of your own code intermingled in the core. Instead just add/insert an extra hook in the core and put our actual code into an extension.
   This goes even for third-party add-ons.
   See: http://madebyhippo.com/blog/view/expressionengine_hook_dont_hack