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What is the most efficient way to determine which loop I'm in?

I have a few plugins that alter the query by hooking into various parts of WP_Query::get_posts(), through the usual suspects, ie posts_where, posts_join, etc. I don't want to effect every loop on every page though, so right now I'm running a debug_backtrace() and checking for the existence of the main() or query_posts() function as necessary.

There has to be a more efficient way to identify the primary loop and sub-loops on each page. Something I keep missing when I pore over the query vars and other aspects of the request, something that's unique to each one. How would you go about doing this?

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Any progress on this question? If you've found an answer elsewhere, come back here and post your solution as an answer for others to benefit. – Tom Auger Sep 30 '11 at 20:49
see wordpress.stackexchange.com/questions/28670/…. Also I noticed that using in_the_loop() works too... – onetrickpony Nov 21 '11 at 2:55

Just a quick update that a new method is_main_query() has been introduced in WP 3.3.


add_action( 'pre_get_posts', 'foo_modify_query_exclude_category' );
function foo_modify_query_exclude_category( $query ) {
    if ( $query->is_main_query() && ! $query->get( 'cat' ) )
    $query->set( 'cat', '-5' );


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If secondary loops are called properly (i.e. by not mucking with query_posts(), and by setting a variable $myloop equal to get_posts() or new WP_Query), then identifying said loop is as simple as referencing the variable.

If you need to call a second loop from within the primary Loop, and you call setup_postdata() in the secondary loop, you may need to call wp_reset_query() when you close your secondary loop, so that your template tags revert to applying to the primary Loop.

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Thanks Chip, but I probably should have mentioned that the plugin is most likely unaware of its environment to that degree. I won't be responsible for every theme that the plugin is running in and unable to ensure that each one is using the loop appropriately. – mwaterous Jun 22 '11 at 9:07

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