How add a group by to the query used by the media library?

Question

What would be the proper way to add a group by to the media library query? What I have tired so far is not working:

add_filter('posts_groupby ', 'limitMediaLibraryItems', 10, 2 );
function limitMediaLibraryItems($groupby) {

    if ( strpos( $_SERVER[ 'REQUEST_URI' ], '/wp-admin/upload.php' ) !== false ) {    
        $groupby .= " guid";
    }

    return $groupby;
}

Updated: Maybe the correct approach is to use the ajax_query_attachments_args filter. How could this be made to work?

add_filter( 'ajax_query_attachments_args', 'hide_duplicate_guids', 10, 1 );

function hide_duplicate_guids( $query = array() ) {

    $query['group by'] = 'guid';

    return $query;

}

Answer 1

I found a solution; use pre_get_posts:

add_action( 'pre_get_posts', 'modify_attachments' );

function modify_attachments( $query ) {
    if ( is_admin() && strpos( $_SERVER[ 'REQUEST_URI' ], 'admin-ajax.php' ) !== false ) {      
        add_filter( 'posts_groupby', 'group_attachments' );
    }
 return $query;
}

function group_attachments( $groupby ) {  
    $groupby .= " guid";
    return $groupby;        
}