WP_Query | Help me create a search term with an ‘OR’ relation?

(Revised on March 25 2020 UTC)

So in this revised answer, I’ll just begin with the code:

1. Define the variables: (I intentionally included only the $args part)

   // define POSTed/submitted variables here like $paged, $display_count and $direction
   
   // define the offset/'direction' stuff here
   
   // then define your $args array
   $args = array(
       'post_type'      => 'product',
       'post_status'    => 'publish',
       'orderby'        => 'menu_order',
       'order'          => 'ASC',
       'posts_per_page' => $display_count,
       // You should use 'paged' and not 'page'.
       'paged'          => $paged,
       'offset'         => $offsetcalc >= 1 ? $offsetcalc : '',
       'tax_query'      => array(),
   );
   

2. And here’s the main code, for the “search term OR”:

   // This is basically $args['tax_query'], except that we *don't* add it to $args.
   $tax_query = array();
   
   if ( ! empty( $search_tags ) ) {
       $tax_query[] = array(
           'taxonomy' => 'product_tag',
           'terms'    => wp_parse_slug_list( $search_tags ),
           'field'    => 'slug',
       );
   }
   
   if ( ! empty( $search_categories ) ) {
       $tax_query[] = array(
           'taxonomy' => 'product_cat',
           'terms'    => wp_parse_slug_list( $search_categories ),
           'field'    => 'slug',
       );
   }
   
   if ( ! empty( $tax_query ) ) { // if empty, don't set the relation
       $tax_query['relation'] = $search_relation;
   }
   
   $_filter = true; // a (private) var for the closure below
   add_filter( 'posts_clauses',
   function ( $clauses ) use ( &$_filter, $search_term, $tax_query ) {
       if ( ! $_filter ) {
           return $clauses;
       }
   
       global $wpdb;
   
       $search_where="";
       if ( $search_term ) {
           $like="%" . $wpdb->esc_like( $search_term ) . '%';
           $search_where = $wpdb->prepare( "$wpdb->posts.post_title LIKE %s", $like );
       }
   
       if ( ! empty( $tax_query ) ) {
           $tax_query = new WP_Tax_Query( $tax_query );
           $is_and = ( 'AND' === $tax_query->relation );
   
           $tax_query = $tax_query->get_sql( $wpdb->posts, 'ID' );
           if ( empty( $tax_query['where'] ) ) { // just in case..
               if ( $search_where ) {
                   $clauses['where'] .= " AND ( $search_where )";
               }
               return $clauses;
           }
   
           $clauses['join'] .= $tax_query['join'];
           if ( $is_and ) {
               $clauses['where'] .= $search_where ?
                                    " AND ( $search_where ) {$tax_query['where']}" :
                                    $tax_query['where'];
           } else {
               $where = preg_replace( '/^ *AND\b/', '', $tax_query['where'] );
               $clauses['where'] .= $search_where ?
                                    " AND ( ( $search_where ) OR{$where} )" :
                                    $tax_query['where'];
           }
           $clauses['groupby'] = "$wpdb->posts.ID";
       } elseif ( $search_where ) {
           $clauses['where'] .= " AND ( $search_where )";
       }
   
       return $clauses;
   } );
   
   $the_query = new WP_Query( $args );
   $_filter = false; // disable the filter, to avoid issues with other WP_Query calls
   

A bit of explanation (for code #2 above)

What you’re looking for is a WHERE clause that looks something like:

(There are other conditions/variations, but this is the main one)

WHERE post_type="product" AND (
  ( post_title LIKE '%<search term>%' ) # Find posts that matched the search term,
  OR ( product_tag IN (<ids/slugs>) )   # ..or those that are in the specified tags
  OR ( product_cat IN (<ids/slugs>) )   # ..or categories.
)

So in that code #2 above, I’m using the posts_clauses hook to add that WHERE clause (and do other relevant stuff), but for generating the proper SQL clauses for the taxonomy (tag/category) queries, I’m using WP_Tax_Query (which is what WP_Query uses, btw).

Additional Notes

1. I’m using wp_parse_slug_list() to parse the (comma-separated) tags and categories into an array of slugs. And you should also be using it to make sure we have a valid array and because the function just works well. 🙂

2. Remember that if offset is 0, then in the $args, the offset should be set to '' (i.e. an empty string) instead of 0, to make sure the $paged works as expected.

3. Just a personal note… sorry, I forgot about using WP_Tax_Query before. 😉