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I'm trying to use nested loops with the posts to posts plugin. The loops both work, but the problem arises after the second nested loop ($issue). I want to access the $publication loop again, but the data is still the $issue data.

wp_reset_query() will reset right back to the main loop in single.php which I don't want.

I could use get_posts() instead of new WP_Query, but I want to be able to use get_template_part().

How can I reset my data back to the publication loop, so that the second 'Publication title' returns the publication, not the issue, title?

Here's my code within single.php:

$publication = new WP_Query( array(
'connected_type'  => 'publication_to_post',
'connected_items' => $post->ID,
'fields'          => 'ids',
'posts_per_page'  => 1,
) );

if ( $publication->have_posts() ) {
while ( $publication->have_posts() ) : $publication->the_post();
    echo '<h2>Publication title = '.get_the_title().'</h2>';
    $pub_id = get_the_ID();

    $issue = new WP_Query( array(
        'connected_type'  => 'publication_to_issue',
        'connected_items' => $pub_id,
        'fields'          => 'ids',
        'posts_per_page'  => 1,
    ) );

    if ( $issue->have_posts() ) {
        while ( $issue->have_posts() ) : $issue->the_post();

            // need to be able to use template parts in here
            echo '<h2>Issue title = '.get_the_title().'</h2>';

        endwhile;
    }

    // This currently returns the issue title, not the publication title
    echo '<h2>Publication title = '.get_the_title().'</h2>';

endwhile;
}
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2 Answers 2

I'm going to answer this myself, but it was the very clever @simonwheatley of Code for the People that solved this one for me.

Instead of using wp_reset_postdata() or wp_reset_query(), you can use the following:

$publication->reset_postdata();

Where $publication is your query object.

The working code now looks like:

$publication = new WP_Query( array(
'connected_type'  => 'publication_to_post',
'connected_items' => $post->ID,
'fields'          => 'ids',
'posts_per_page'  => 1,
) );

if ( $publication->have_posts() ) {
while ( $publication->have_posts() ) : $publication->the_post();
    echo '<h2>Publication title = '.get_the_title().'</h2>';
    $pub_id = get_the_ID();

    $issue = new WP_Query( array(
        'connected_type'  => 'publication_to_issue',
        'connected_items' => $pub_id,
        'fields'          => 'ids',
        'posts_per_page'  => 1,
    ) );

    if ( $issue->have_posts() ) {
        while ( $issue->have_posts() ) : $issue->the_post();

            // need to be able to use template parts in here
            echo '<h2>Issue title = '.get_the_title().'</h2>';

        endwhile; $publication->reset_postdata();
    }

    echo '<h2>Publication title = '.get_the_title().'</h2>';

endwhile;
}
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Indeed, this is the much smarter way to do this. –  David Dec 13 '13 at 10:16

First of all, I think it's possible to use get_posts() in combination with setup_postdata(). With these, you can use the template tags as in a normal WordPress loop.

But you can use this function also in your nested loops:

# make sure $post is the global in your scope (which should be the case in single.php)
global $post;
if ( $publication->have_posts() ) {
while ( $publication->have_posts() ) : $publication->the_post();
    echo '<h2>Publication title = '.get_the_title().'</h2>';
    $pub_id = get_the_ID();

    # preserve the current post in the higher loop
    $preserve_post = get_post();

    $issue = new WP_Query( array(
        'connected_type'  => 'publication_to_issue',
        'connected_items' => $pub_id,
        'fields'          => 'ids',
        'posts_per_page'  => 1,
    ) );

    if ( $issue->have_posts() ) {
        while ( $issue->have_posts() ) : $issue->the_post();

            // need to be able to use template parts in here
           echo '<h2>Issue title = '.get_the_title().'</h2>';

        endwhile;
    }

    # set the global back to your first loop post
    $post = $preserve_post;
    setup_postdata( $post );
    // This currently returns the issue title, not the publication title
    echo '<h2>Publication title = '.get_the_title().'</h2>';

endwhile;
}
wp_reset_query();
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