workshop.md

# WorkShop: Deep Dive into WordPress' WP_Query The Atlanta WordPress Coder's Guild

• Presenters: @mikeschinkel / @wpscholar
• Twitter: @thecodersguild
• Hashtags: #wp_query #awcgs

###Setup

• Presentation: Just follow along.

• Workshop: Set up a child theme:

  • themes/thecodersguild/style.css

      /*
      Theme Name: The Coder's Guild
      Template:   twentyfifteen
      Version:    0.1
      */
      @import url( "../twentyfifteen/style.css" );
    

  • themes/thecodersguild/functions.php

      <?php
      
      class TheCodersGuild_Theme {
      	static function on_load() {
      		// We will add hooks here
      	}
      }
      TheCodersGuild_Theme::on_load();
    

###Intro:

• Review The Outline
• What is WP_Query?
  • A PHP class
  • WP's feature to return a list of Posts from the DB
  • For the Workshop:
    • Create a "Meetups" page in WP
    • Copy page.php from parent theme to page-meetups.php
    • Unzip EventPress Redux into mu-plugins
    • Add plugin-loader.php into mu-plugins
    • Add "Camp Style", "Conference" and "Meetup" to Events > Event Type
    • Add Venues:
      • StrongBox West
      • The Loudermilk Center
      • The Westin Lake Las Vegas
      • Pennsylvania Convention Center
    • Add Events with:
      • 2 AWCG Meetups held at StrongBox West: Plugins 10-28-2005 & WP_Query 11-18-2005
      • 1 Camp Style held at The Loudermilk Center: Atlanta WordCamp March 27-29, 2015
      • 1 Conference held at The Westin Lake Las Vegas: LoopConf May 4-6, 2015
      • 1 Conference + Camp Style held at Pennsylvania Convention Center: WordCamp US Dec 4-6, 2015

Overview of WP_Query usage

• For the Workshop:

  • Go to https://generatewp.com/wp_query/

• What does WP_Query allow querying?

  • Post fields
    • ID, post_name, post_type, post_parent, post_author, date fields, etc.
    • Freeform text match in content
  • Post Meta
  • Related Taxonomy Terms
  • Author Names

• WP_Query allows Subsetting and Ordering

  • Pagination
  • Order

• WP_Query allow Hiding and Caching

  • Permissions
  • Caching

• References

  • https://codex.wordpress.org/Class_Reference/WP_Query
  • http://code.tutsplus.com/series/mastering-wp_query--cms-818
  • https://generatewp.com/wp_query/

###Basic WP_Query Usage

• With The Loop:

    $query = new WP_Query( array( 'post_type' => 'epr_event' ) );
    while ( $query->have_posts() ) : $query->the_post();
    	echo '<h3>' . get_the_title( $query->post ) . '</h3>';
    endwhile;			
  

• Using directly:

    $query = new WP_Query( array( 'post_type' => 'epr_event' ) );
    foreach( $query->posts as $post ):
    	echo '<h3>' . get_the_title( $post ) . '</h3>';
    endforeach;
  

• Automatically used by WordPress on every page load:

    global $wp_query, $wp_the_query	
  

• Vs. query_posts() and get_posts()

  • $posts = query_posts(): Not recommended

      query_posts( array( 'post-type' => 'page' )  );
      // You can now do the loop here
    

  • get_posts(): Ok

      $posts = get_posts( array( 'post-type' => 'page' )  );
    

• Using wp_reset_postdata()

  • Use after using "The Loop"
  • Better: Don't use The Loop!

Intermediate WP_Query Usage

• Query by Taxonomy Terms:

  • WP_Query parameter:

    • tax_query
    • For the Workshop:

      • Add the following parameter to inside array passed to WP_Query in page-meetup.php:

          'tax_query' => array(
              array(
                  'taxonomy' => 'epr_event_type',
                  'field'    => 'slug',
                  'terms'    => 'meetup',
              ),
          ),
        

  • tax_query parameter:

    • For the Workshop:

      • Change the inside of the array passed to WP_Query in page-meetup.php to:

          'tax_query' => array(
              'relation' => 'AND',
              array(
                  'taxonomy' => 'epr_event_type',
                  'field'    => 'slug',
                  'terms'    => 'conference',
              ),
              array(
                  'taxonomy' => 'epr_event_type',
                  'field'    => 'slug',
                  'terms'    => 'camp-style',
              ),
          ),
        

• Query by Meta Fields

  • meta_key, meta_value, meta_compare

    • For the Workshop:

      • Replace the tax_query in page-meetup.php with:

          'meta_key'     => '_epr_event[venue_id]',
          'meta_value'   => 19,
          'meta_compare' => '=',
        

  • meta_query

    • For the Workshop:

      • Replace the meta_*** args in page-meetup.php with:

          'meta_query' => array(
              'relation' => 'OR',
              array(
          	    'key' 	 	=> _'epr_event[venue_id]',
              	'value'   	=> 19,
          	    'compare'   	=> '=',
              ),
              array(
          	    'key' 	 	=> _'epr_event[venue_id]',
          	    'value'   	=> 44,
          	    'compare'   	=> '=',
              ),
          ),
        

    • For the Workshop:

      • Replace the meta_query args in page-meetup.php with:

          $sbw = new WP_Query( array(
          	'fields' => 'ids',
           	'post_type' => 'epr_venue',
           	'name' => 'strongbox-west'
          ));
        
          $tlc = new WP_Query( array(
          	'fields' => 'ids',
          	'post_type' => 'epr_venue',
          	'name' => 'the-loudermilk-center'
          ));
        
          $query = new WP_Query( array(
          	'post_type' => 'epr_event',
          	'meta_query' => array(
          	    array(
          			'key'      => '_epr_event[venue_id]',
          			'compare'   => 'IN',
          			'value'   	=> array(
          				$sbw->posts[0],
          				$tlc->posts[0],
          			),
          		),
          	),
          ));
        

• Using Hooks

  • 'pre_get_posts'

    The action hook pre_get_posts is primarily for us with the main query:

    • For the Workshop:

      • Add to functions.php to display (blog) posts alphabetically on home page.

          add_filter( 'pre_get_posts', 'tcg_pre_get_posts' );
          function tcg_pre_get_posts( $query ) {
          	if ( $query->is_home() && $query->is_main_query() ) {
          		$query->set( 'order', 'ASC' );
          		$query->set( 'orderby', 'title' );
          	}
          }
        

    • Modify the Query for Loop using “pre_get_posts”

    • Modifying the current query with pre_get_posts

    • The Dangers of Using pre_get_posts in WordPress (incorrectly)

  • 'posts_clauses'

    • See examples below in "Modifying SQL" section

• Optimization

  • $nopaging
  • $no_found_rows
    • Found rows not needed for $nopaging
    • Might be needed for custom code.

Advanced WP_Query Usage

• Modifying SQL

  • When do you need to modify SQL?

    • When you can't achieve what you need just with WP_Query

  • Workshop: Add this to functions.php:

      	add_filter( 'query_vars', 'tcg_query_vars' );
      	function tcg_query_vars( $query_vars ) {
      		$query_vars[] = 'epr_meetups_query';
      		return $query_vars;
      	}
    
      	add_filter( 'posts_clauses', 'tcg_posts_clauses', 10, 2 );
      	function tcg_posts_clauses( $clauses, $query ) {
      		global $wpdb;
      		if ( $query->get( 'epr_meetups_query' ) ) {
      			$clauses['fields'] = "{$wpdb->posts}.ID,{$wpdb->posts}.post_title";
      		}
      		return $clauses;
      	}
    

  • Note use of $wpdb->posts for table name

• Caching Queries

  • Using Object Cache for hosting with Persistent Cache

      $query = wp_cache_get( $cache_key = "meetups_query" );
      if ( ! $query ) {
      	$query = new WP_Query( array(
      			'post_type'         => 'epr_event',
      			'posts_per_page'    => 999,
      		);
      	);
      	wp_cache_set( $cache_key, $query, 'eventpress-redux', 5*60 );
      }
    

  • Using Transients for hosting w/o Persistent Cache

      $query = get_transient( $transient_key = "epr_meetups_query" );
      if ( ! $query ) {
      	$query = new WP_Query( array(
      			'post_type'         => 'epr_event',
      			'posts_per_page'    => 999,
      		);
      	);
      	set_transient( $transient_key, $query, 5*60 );
      }
    

  • For When Query $args can change

      $args = array(
      	'post_type'         => 'epr_event',
      	'posts_per_page'    => 999,
      	/* More options that differ based on user action */
      );
      $key = md5( serialize( $args ) );
      $query = wp_cache_get( $cache_key = "meetups_query[{$key}]" );
      if ( ! $query ) {
      	$query = new WP_Query( $args );
      	wp_cache_set( $cache_key, $query, 'eventpress-redux', 5*60 );
      }
    

• Setting 404

    $wp_query->set_404();
    status_header( 404 );
    nocache_headers();
  

• Best Practice

  • Always modify query SQL and/or behavior based on an argument
    • e.g. 'epr_meetups_query'
    • Not based on globals or other implicit state
    • Except Main Query
      • Use 'main_query[{$key}]' for caching
      • Where $key = md5( $_SERVER['REQUEST_URI'] );

Other Hook List

8. More Specific Hooks

   • 'posts_where'
   • 'posts_join'
   • 'posts_orderby'
   • 'posts_distinct'
   • 'post_limits'
   • 'posts_fields'
   • 'posts_groupby'

9. Request Hooks

   • 'posts_where_request'
   • 'posts_groupby_request'
   • 'posts_join_request'
   • 'posts_orderby_request'
   • 'posts_distinct_request'
   • 'post_limits_request'
   • 'posts_fields_request'
   • 'posts_clauses_request'

10. Other Hooks

    • 'posts_selection'
    • 'parse_tax_query'
    • 'posts_search'
    • 'posts_search_orderby'
    • 'comment_feed_join'
    • 'comment_feed_where'
    • 'comment_feed_groupby'
    • 'comment_feed_orderby'
    • 'comment_feed_limits'
    • 'posts_where_paged'
    • 'posts_join_paged'
    • 'posts_request'
    • 'split_the_query'
    • 'posts_request_ids'
    • 'posts_results'
    • 'the_preview'
    • 'the_posts'
    • 'found_posts_query'
    • 'found_posts'
    • 'content_pagination'
    • 'old_slug_redirect_url'
    • 'wp_search_stopwords'