Is it necessary to use wp_reset_query() in a WP_Query call?

Question

I'm using the following code to retrieve posts:

<?php
$featuredPosts = new WP_Query();
$featuredPosts->query('showposts=5&cat=3');
while ($featuredPosts->have_posts()) : $featuredPosts->the_post(); ?>
<h1><a href="<?php the_permalink() ?>"><?php the_title(); ?></a></h1>
<div class="meta">
By <?php the_author() ?>
</div>
<div class="storycontent">
<?php the_excerpt(); ?>
</div>
<?php endwhile; ?>

Do I need to use wp_reset_query() If I have to use it where should I place it?

Answer 1

Hi @janoChen:

Simple answer: no.

What follows is what the PHP code for the function wp_reset_query() from /wp-includes/query.php in WordPRess v3.0.4 as well as the functions subsequently called. You can see that it's primarily about in modifying global variables.

When you use new WP_Query($args) you will be assigning the return value from values to a local variable so, unless you are doing something so complex that you'd already know the answer to this question for then no, you don't need to call wp_reset_query():

function wp_reset_query() {
  unset($GLOBALS['wp_query']);
  $GLOBALS['wp_query'] =& $GLOBALS['wp_the_query'];
  wp_reset_postdata();
}

function wp_reset_postdata() {
  global $wp_query;
  if ( !empty($wp_query->post) ) {
    $GLOBALS['post'] = $wp_query->post;
    setup_postdata($wp_query->post);
  }
}

function setup_postdata($post) {
  global $id, $authordata, $day, $currentmonth, $page, $pages, $multipage, $more, $numpages;

  $id = (int) $post->ID;

  $authordata = get_userdata($post->post_author);

  $day = mysql2date('d.m.y', $post->post_date, false);
  $currentmonth = mysql2date('m', $post->post_date, false);
  $numpages = 1;
  $page = get_query_var('page');
  if ( !$page )
    $page = 1;
  if ( is_single() || is_page() || is_feed() )
    $more = 1;
  $content = $post->post_content;
  if ( strpos( $content, '<!--nextpage-->' ) ) {
    if ( $page > 1 )
      $more = 1;
    $multipage = 1;
    $content = str_replace("\n<!--nextpage-->\n", '<!--nextpage-->', $content);
    $content = str_replace("\n<!--nextpage-->", '<!--nextpage-->', $content);
    $content = str_replace("<!--nextpage-->\n", '<!--nextpage-->', $content);
    $pages = explode('<!--nextpage-->', $content);
    $numpages = count($pages);
  } else {
    $pages = array( $post->post_content );
    $multipage = 0;
  }

  do_action_ref_array('the_post', array(&$post));

  return true;
}

-Mike

Answer 2

If you are using custom query like this

$cat = new WP_query(); 
$cat->query("cat=19,20,-23&showposts=5&orderby=rand"); 
while ($cat->have_posts()) : $cat->the_post(); 
  $data = get_post_meta( $post->ID, 'key', true );
$img_arrays []= $data['productimage']; 
$lnk_arrays[] =get_permalink($post_ID); 
endwhile; 
wp_reset_query(); 

Then you won't run into problems. Otherwise, if on the same page there is another loop you are bound to get some unexpected results. I didn't used wp_reset_query() in the above code (which was placed in my header.php file. Then when i got into single.php mostly i get the detail pages of other categories which was frustrating. Later, i realized that i forgot to reset the query at the top. Soon, it started working like a charm.

Answer 3

It is not necessary for WP_Query by itself, but it is necessary (or at least good thing to do) if you use any related functions/methods ( such as the_post() or setup_postdata() ) to fill global variables with your data.

Basically creating new WP_Query object is merely data retrieval, but using it to run active loop and making data accessible to template tags does modify environment and it is good to reset everything afterwards.

Overall - it isn't meaningful performance penalty to call it, so it is easier to always call it than deciding if you should or forgetting about it and having something mysteriously broken.

Update

wp_reset_postdata() function seems to be more fitting choice. wp_reset_query() resets global $wp_query (which custom WP_Query object doesn't affect) and $post (which it might as above) variables. wp_reset_postdata() only restores $post, which should be enough.