What is wrong with this pagination code?

Question

I'm trying a new approach to paginate posts returned in a category.php file. I want to see snippets of 10 posts at a time. Filename is category-xyz.php and this worked before I changed to this method, although I was using showposts=200 and it was returning all 180 posts in that category.

I changed method because several calls I used were deprecated (eg showposts) or not advised. I am using this post's solution for reference:

How to fix pagination for custom loops?

Here's my code:

<?php
// Define custom query parameters
$custom_query_args = array( 
'cat' => 76, 
'posts_per_page' => 5
);

// Get current page and append to custom query parameters array
$custom_query_args['paged'] = get_query_var( 'paged' ) ? get_query_var( 'paged' ) : 1;

// Instantiate custom query
$custom_query = new WP_Query( $custom_query_args );

// Pagination fix
$temp_query = $wp_query;
$wp_query   = NULL;
$wp_query   = $custom_query;

        // Output custom query loop rather than use wp_query
        if ( $custom_query->have_posts() ) : 
             while ( $custom_query->have_posts() ) : 
              $custom_query->the_post();
        // Loop output goes here
        ?>
            <div class="pcrmbimgholder">
            <a href="<?php the_permalink() ?>" rel="bookmark"><img src="<?php echo pcrmbimagegrab() ?>" alt="<?php the_title(); ?>" /></a>
            </div>
        <h2><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></h2>
        <?php the_content_limit(190, ""); ?>                
                <?php $customField = get_post_custom_values("price"); 
                 if (isset($customField[0])) { 
                 echo "<strong>Price: ".$customField[0];
                 echo "   </strong>";
                } else { 
                ;
                }
                ?>  
                <?php $customField = get_post_custom_values("sku"); 
                 if (isset($customField[0])) { 
                 echo "&#124;   Stock Reference: ".$customField[0] . "&#32;&#32;&#32;";
                } else { 
                ;
                }
                ?>      
        <a class="postbutton" href="<?php the_permalink() ?>" rel="bookmark"><span>View</span></a><div class="separator"></div>     


        <?php

    endwhile;
endif;
// Reset postdata
wp_reset_postdata();

// Custom query loop pagination
previous_posts_link( 'Older Posts' );
next_posts_link( 'Newer Posts', $custom_query->max_num_pages );

// Reset main query object
$wp_query = NULL;
$wp_query = $temp_query;

?>

I have also tried this because I am not sure which parameters I need in the custom query array:

// Define custom query parameters
$custom_query_args = array( 
'cat' => 76, 
'posts_per_page' => 5,
'max_num_pages' => 20,
'paged' => $paged,
);

The pagination link goes to /category/category-name/page/2/ which results in a 404 error. Any ideas why?

Answer 1

The main query runs before the template is loaded, and WordPress decides what template to load based on the results of that query.

You say your default posts_per_page is set to 200, and there are 180 posts in that category, so as far as WordPress knows, there is no page 2. Your custom query that you run in the template with a different posts per page setting is unrelated to the main query.

The solution is to make adjustments to the main query before the template is loaded, via the pre_get_posts action. This would go in your theme's functions.php file:

function category_posts_per_page( $query ) {
    if ( !is_admin()
        && $query->is_category()
        && $query->is_main_query() ) {
        $query->set( 'posts_per_page', 5 );
    }
}
add_action( 'pre_get_posts', 'category_posts_per_page' );

You can then run the normal loop in the template and pagination will work as expected. Also see is_category() in Codex if you want this to apply to a specific single category.