[wp-hackers] pre_get_posts alternatives

[Mike Schinkel]

On Mon, Sep 27, 2010 at 4:05 PM, scribu <mail at scribu.net> wrote:
> On Mon, Sep 27, 2010 at 4:20 PM, Christian Foster <
> christian.foster at gmail.com> wrote:
> 
>> Hi,
>> 
>> I am hooking into pre_get_posts to filter certain post types on
>> taxonomy templates however I have realised this is also affecting any
>> other get_posts. Is there an alternative that will only effect the
>> main loop?
>> 
> 
> You can check for the global $wp_query object:
> 
> add_action( 'pre_get_posts', 'amp_filter' );
> function amp_filter( $query )
> {
>   if ( $query === $GLOBALS['wp_query'] && is_tax('locations') ) {
>       $query->set( 'posts_per_page', 25 );
>   return $query;
> }

Unfortunately that logic will fail if someone is using rewindposts() or query_posts() in a theme(see [1].) Here are a pair of hooks that won't have that problem.  Note that the "is_main_loop" property is not a standard property of the $wp_query object, it's something I added for this purpose:

add_action( 'parse_request', 'mytest_parse_request' );
function mytest_parse_request( $wp ) {
	global $wp_query;
	$wp_query->is_main_loop = true;
	return $wp;
}
add_action( 'pre_get_posts', 'mytest_pre_get_posts' );
function mytest_pre_get_posts( $query ) {
  if ( isset($query->is_main_loop) && $query->is_main_loop) {
    $query->set( 'posts_per_page', 25 );
    $wp_query->is_main_loop = false;
  }
  return $query;
}

Hope this helps.

-Mike
[1] http://codex.wordpress.org/The_Loop#Loop_Examples_2