Create a query from a single category slug

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The function below creates a WP_Query object and takes two variables. $cat – category slug and $per_page – how much posts should be displayed per page.

 /* Create WP_Query from category slug and output it to a variable
 * @param  string $cat      category slug
 * @param  int    $per_page posts per page
 * @return obj    returns WP_Query object
 */

function do_cat_query( $cat, $per_page )
{
  $cat_obj = get_category_by_slug( $cat );
  $cat_id = $cat_obj->term_id;
  $paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;

  // WP_Query arguments
  $args = array(
    'post_type'              => 'post',
    'cat'                    => $cat_id,
    'posts_per_page'         => $per_page,
    'paged'                  => $paged,
    'order'                  => 'DESC',
    'orderby'                => 'date'
  );

  // The Query
  $query = new WP_Query( $args );

  return $query;
}

To use it simply to rewrite the $wp_query in that template as shown below.

$wp_query = do_cat_query('stories', 5);

This will give you the option to use all features just as a normal page however if you need to save the initial query data for later use, assign it to a different variable before overwriting $wp_query.

Like so:

$page_query = $wp_query;
$wp_query = do_cat_query('stories', 5);

Now you can use the initial query as shown below:

<?php if (have_posts()) : while (have_posts()) : the_post(); ?>