WordPress Query Multisite

This is a custom version of WP_Query_Multisite, by ericandrewlewis, to support multisite post queries but without changing the class declaration, we will use the good ol' WP_Query. Just by entering the custom query var multisite => 1 on your query args and your query is now global.

Example usage

$query = new WP_Query( array('multisite' => '1' ) );
while($query->have_posts()) : $query->the_post();
    echo $blog_id . get_the_title() . "<BR>";
endwhile; 
wp_reset_postdata();

To modify what sites are queried, create a 'sites' element in the $args in the constructor parameter, with a sub-element of either 'sitesin' or 'sitesnot_in', which will be an array similar to 'posts__in' in the WP_Query object.

$args = array(
    'multisite' => 1,
    'sites__in' => array( 1, 2, 3, 5)
);
$query = new WP_Query( $args );
while($query->have_posts()) : $query->the_post();
    echo $blog_id . get_the_title() . "<BR>";
endwhile; 
wp_reset_postdata();

Automatic multisite search example

On your functions.php:

include_once(TEMPLATEPATH . '/path/to/multisite-query.php');

function my_multisite_search($query) {
    if(!is_admin() && $query->is_main_query() && $query->is_search) {
        $query->set('multisite', 1);
    }
}
add_action('pre_get_posts', 'my_multisite_search');