Query with pre_get_posts to get pagination

Question

After pretty much getting everything working with query_posts, I noticed my pagination wasn't running. I was told pre_get_posts should be the solution.

My problems:

1. I don't know how to pass all my criteria (query_posts(array('post_type' => 'trips', 'types' => $types, 'paged' => $paged,)in to pre_get_posts

2. I can't get it working on (just) the template I want, which is used on a page (is_page doesn't work)

   Any help would be appreciated.

This is what's inside functions.php

function bwpm_pre_get_posts($query){
    if(!$query->get('posts_page_page'))
    $query->set('posts_per_page',1);
    }
    add_action('pre_get_posts','bwpm_pre_get_posts');

This is what's in the template that is used on the page.

<?php
/*
Template Name: Generic Trips Template
*/
?>
<?php get_header(); ?>

        <?php get_template_part( "beforeloop", "page" ) ?>
                                    <?php $types = $post->post_name; ?>


<?php if (have_posts()) : ?>
    <?php 
        $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
        query_posts(array( 
            'post_type' => 'trips', 
            'types' => $types, 
            'paged' => $paged,
        ) );
    ?>
<?php while (have_posts()) : the_post(); ?>
    <article id="post-<?php the_ID(); ?>" class="post"></article>

<?php endwhile; ?>

<div style="text-align:center;">
<?php posts_nav_link(' &#183; ', 'previous page', 'next page'); ?>
</div>

<?php endif; wp_reset_query(); ?>
        <?php get_template_part( "afterloop", "page" ) ?> 

<?php get_footer(); ?>

Update: 11/06/2012 After updating the code to @chipbennet example, the problem still isn't solved as I don't get properly working pagination. The previous link will never appear, and the next link will show the same content on every page. Full page code can be found on http://pastebin.com/NiuSEWia.

Answer 1

It appears that you want to create a custom page template to display a custom post type? If so, you don't really need to mess with pre_get_posts at all.

First, create your custom page template. I assume you've already done this.

Second, you need to create a custom query, using WP_Query():

global $post;
$types = $post->post_name;

$trips_query_args = array( 
    'post_type' => 'trips', 
    'types' => $types, 
);

$trips_query = new WP_Query( $trips_query_args );

(Note: what is the 'types' parameter? As far as I know, it's not a core query parameter. Are you using it somehow?)

Third, we need to let WordPress know that it needs to base pagination on our custom query rather than on the default query:

global $wp_query;
// Put default query object in a temp variable
$tmp_query = $wp_query;
// Now wipe it out completely
$wp_query = null;
// Re-populate the global with our custom query
$wp_query = $trips_query;

At this point, we've moved the default query into a temporary variable, and re-populated the $wp_query global with our custom query.

Fourth, we need to output our custom query loop:

if ( $trips_query->have_posts() ) : while ( $trips_query->have_posts() ) : $trips_query->the_post();

    // Normal loop output goes here
    // You can use loop template tags normally
    // such as the_title() and the_content()

endwhile; endif;

Just put your loop output into the above. I've omitted it for brevity.

Fifth, we just need to reset things:

// Restore original query object
$wp_query = $tmp_query;
// Be kind; rewind
wp_reset_postdata();

This should be all you need to output a custom query loop, with proper pagination.

Edit

The use of taxonomy {slug} => {term} as a query taxonomy parameter was deprecated in WordPress 3.1, in favor of 'tax_query'. You should replace this:

'types' => $types

...with this:

'tax_query' => array(
    array(
        'taxonomy' => 'types',
        'field'    => 'slug',
        'term'     => $types
    ) 
)

This would make your $types_query_args array look like this:

$trips_query_args = array( 
    'post_type' => 'trips', 
    'tax_query' => array(
        array(
            'taxonomy' => 'types',
            'field'    => 'slug',
            'term'     => $types
        ) 
    )
);

Edit

@ChipBennett interesting development. I added 'paged' => N to the $trips_query_args array, where N stands for a number. When adding 1 the page actually shows exactly the perfect results for page 1. When adding 2 it shows the perfect results for page 2. However when using the navigation links OR even manipulating the URL, it no longer works. Any ideas?

So, let's try forcing the query pagination, using the following:

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

You would update your $trips_query_args array accordingly:

$paged = ( get_query_var( 'paged') ) ? get_query_var( 'paged' ) : 1;

$trips_query_args = array( 
    'post_type' => 'trips', 
    'tax_query' => array(
        array(
            'taxonomy' => 'types',
            'field'    => 'slug',
            'term'     => $types
        ) 
    ),
    'paged'    => $paged;
);

Does that result in correct pagination?

Answer 2

WordPress figures pagination details based on the main query, and before the template is parsed. Which is probably why somebody recommended that you leverage pre_get_posts.

I don't know what the "beforeloop" and "afterloop" template parts in your code are for, but it looks like you're trying to let the main (page) query stand for the page header, then switch to a custom query, then switch back to the main query with wp_reset_query(). This approach won't work if you expect pagination to function properly, and is not a recommended approach to multiple queries in general. If you want two queries on a page, one of them should be a custom query using WP_Query or something similar.

You can either:

• Determine if there's a natural WP equivalent of the page you're trying to create (for example, it look slike you're trying to create a post type archive, or a custom taxonomy term archive), and use this natural template instead. Check the Template Hierarchy.

• Change the entire main query using pre_get_posts, and get anything else you need (the stuff currently in the beforeloop and afterloop) using a custom query. You can set all query params in pre_get_posts the same way you've set the posts_per_page param. For example:

  $query->set('posts_per_page',1); $query->set('post_type','trips');

Etc. You shouldn't need to manipulate the paged var if you're paginating based on the main query like this.

Answer 3

I solved this issue using pre_get_post. I found one implementation that works for me:

if ( ! function_exists( 'ucc_add_cpts_to_pre_get_posts' ) ) {
    function ucc_add_cpts_to_pre_get_posts( $query ) {
        if ( $query->is_main_query() && ! is_post_type_archive() && ! is_singular() && ! is_404() ) {
            $my_post_type = get_query_var( 'post_type' );
            if ( empty( $my_post_type ) ) {
                $query->set('post_type', 'your_custom_type');
                $query->set('posts_per_page', 'your_posts_per_page');
            }
        }
    }
}
add_action( 'pre_get_posts', 'ucc_add_cpts_to_pre_get_posts' );

http://uncommoncontent.com/2012/01/28/add-custom-post-types-to-the-loop You must remove query_posts from your template.