title: Extending the CI_DB_active_record class in codeigniter 2.0
body: <p>I am writing my first program with Codeigniter, and have run into a problem.  I will start with a focused description of the problem and can broaden it if I need to:</p>
  
  <p>I need to write a multi-dimensional array to the DB and want to use the insert_batch function from the CI_DB_active_record class to do so.  The problem is that I need to write empty values as NULL for some fields while other fields need to be empty strings.  The current function wraps all values with single quotes, and I cannot find a way to write null values to the database for specified fields.</p>
  
  <p>I would also like to increase the number of records per batch.</p>
  
  <p>I see how to extend models, libraries, etc., but is there a way to extend the CI_DB_active_record class without modifying core classes?  The minimal amount of core class modification to make this work that I have found is modifying the following lines in the DB.php file (changing the require_once file to the new file that extends the CI_DB_active_record class and  changing the CI_DB_active_record class name to the new class name):</p>
  
  <pre><code>require_once(BASEPATH.'database/DB_active_rec'.EXT);
  
          if ( ! class_exists('CI_DB'))
          {
              eval('class CI_DB extends CI_DB_active_record { }');
          }
  </code></pre>
  
  <p>Can I do better?</p>