Extending WordPress migration classes

The builtin wordpress_migrate classes can be extended for custom situations, such as mapping incoming postmeta data to node fields. The basic approach:

1. Extend the appropriate class, such as the WordPressBlogEntry class with your custom behavior - add field mappings in __construct(), manipulate the body ($row->content) in prepareRow(), etc.
2. Extend the WordPressBlog class, and override migrationClasses to point to your custom classes:

class MyCustomBlog extends WordPressBlog {
  public function migrationClasses() {
    $classes = parent::migrationClasses();
    $classes['WordPressBlogEntry'] = 'MyCustomBlogEntry';
    $classes['WordPressPage'] = 'MyCustomPage';
    return $classes;
  }
}

3. Set the wordpress_migrate_blog_class variable to point at your WordPressBlog class. For example, add this to settings.php:

$conf['wordpress_migrate_blog_class'] = 'MyCustomBlog';