title: change database connection of codeigniter migration
body: <p>I would like to change database connection of codeigniter migration.</p>
  
  <p>My default database is DB1, But I want to change connection to DB2.</p>
  
  <p>How can I do that? default coding as the following .</p>
  
  <pre><code>defined('BASEPATH') OR exit('No direct script access allowed');
  
  class Migration_Add_blog extends CI_Migration {
  
  public function up()
  {
      $this-&gt;dbforge-&gt;add_field(array(
          'blog_id' =&gt; array(
              'type' =&gt; 'INT',
              'constraint' =&gt; 5,
              'unsigned' =&gt; TRUE,
              'auto_increment' =&gt; TRUE
          ),
          'blog_title' =&gt; array(
              'type' =&gt; 'VARCHAR',
              'constraint' =&gt; '100',
          ),
          'blog_description' =&gt; array(
              'type' =&gt; 'TEXT',
              'null' =&gt; TRUE,
          ),
      ));
  
      $this-&gt;dbforge-&gt;create_table('blog');
  }
  
  public function down()
  {
      $this-&gt;dbforge-&gt;drop_table('blog');
  }
  </code></pre>