Advanced Post Queries

Advanced Post QueriesBest Practices for Accessing your Data @TomAuger WordCamp Montreal 2012

Whats in the database?*• Posts • Users• Pages • User meta• Attachment records • Site Options• Revisions – Your URL• Nav Menus – Widget settings – Theme options• Custom Post Types – User capabilities• Post Meta (maybe)• Categories• Tags• Custom Taxonomies • * basically, everything

Post Queries in the URL (look Ma, no code!)• Settings > Reading – "Your Latest Posts" – / (index.php) – Front page – / (front-page.php) – Posts page – /posts-page-slug/• Page / post slug • /post-or-page-slug/• Category Archive • /category/term/• Date • /year/[month/]• Author Archive • /author/author-nicename/• post_type • /post-type-slug/• Search • /search/term/

Post Queries (code)• query_posts( $args )• new WP_Query( $args )• get_posts( $args )• get_pages( $args )

And where does it go?• Most often on the PHP page template• Widgets defined in plugins• Hooks declared in functions.php or include

query_posts() usage Old Skool• Looks like URL query parameters• Mimics the browser address, so may feel more familiar• Kinda hard to read… query_posts( ‘cat=6&post_type=product&numberposts=5’ );

query_posts() usage The Cool Way…• Supply arguments as array of key => value pairs• Lots more brackets and stuff, but…• Kinda looks cool once you get used to it query_posts( array( ‘cat’ => 6, ‘post_type’ => ‘product’, ‘posts_per_page’ => 5 ) );

What can we query? http://codex.wordpress.org/Class_Reference/WP_Query• author • custom fields (meta)• category / tag / tax • sticky• post name, ID(s) • add pagination• page parent • set sort order and• post type criteria• post status • comment count• date & time • even random posts!

query_posts Example Movie of the Day!• Create a new Page• Only the slug is important• Add query_posts() before any HTML• Current page content is clobbered query_posts( array ( orderby => rand, posts_per_page => 1 ) );• http://localhost/projects/wordcamp/query_posts-example/

query_posts to Limit Page Count?• Common example is to change # posts displayed query_posts( ‘posts_per_page=20’ );• Loads the posts twice*!• Consider Settings > Reading > Blog Pages Show At Most…• * and then some…

What’s up with query_posts()?• http://codex.wordpress.org/Function_Reference/query_posts• Only useful for altering the Main Loop• Can break pagination – (but can be fixed with effort)• Still executes the original query! – (and then some)• Dont use in a subquery!

Why Subqueries?• Add related posts• Add child pages• Add other types of content (eg: News)• Widgets!

Is there a template tag for that?• http://codex.wordpress.org/Template_Tags• Author info (the_author(), the_author_meta() )• Metadata (the_meta() )• Categories, tags• Navigation (eg: next_post_link() )

Template Tag Example• http://localhost/projects/wordcamp/template-tags/• Inside "The Loop", powered by the_post() <div class="post-meta"><?php the_meta() ?></div> <div class="categories"><?php the_category(); ?></div> <div class="tags"><?php the_tags(); ?></div> <div class="nav"> <?php previous_post_link() ?> | <?php next_post_link() ?> </div>

"Real" Sub-queries: WP_Query• The brains behind all queries on the wp_posts table• Defined in wp-includes/query.php• All queries go through WP_Query• "Get your own" with new WP_Query( $args );

WP_Query usage<?php $my_sub_query = new WP_Query( array ( post_type => quotes, order => rand, posts_per_page => 1 ) ); while ( $my_sub_query->have_posts() ){ $my_sub_query->the_post(); get_template_part( my_loop_template ); } wp_reset_postdata();}

WP_Query Examples• http://localhost/projects/wordcamp/date-query/• http://localhost/projects/wordcamp/sort-by-post-meta/

Meta Queries• Make your postmeta work (harder) for you!• At first blush, a little funky <?php $meta_query = new WP_Query( array( meta_query => array( array( // meta query here ) ) ) );

More Meta Query Examples• http://localhost/projects/wordcamp/meta-queries/• http://localhost/projects/wordcamp/multiple-meta-queries-and/• http://localhost/projects/wordcamp/multiple-meta-queries-or/

Taxonomy Queries• As with meta_query, so with tax_query <?php $tax_query = new WP_Query( array( taz_query => array( array( ) ) ) );• http://localhost/projects/wordcamp/tax-query-simple/

wp_reset_postdata()?• If you use the_post(), clean up after yourself• the_post() sets lots of $_GLOBALs• Could break templates, footers, widgets etc…• http://localhost/projects/wordcamp/wp_reset_postdata/

Global Query Manipulation (The Good Stuff!)• Modify the Main Query• Modify the way all queries work site-wide• Modify queries for a specific page

Case Study: amovo.ca• Furniture retailer with multiple brands• Custom post type: "amovo-products"• Custom post type: "manufacturer"• Custom taxonomies: "product-categories" and "product-applications"• http://localhost/projects/amovo/

amovo.ca: Custom Global Sort• Wanted to "feature" certain products• Wherever they might be listed• eg: http://localhost/projects/amovo/product- categories/executive-conference-seating/• Best match: custom field "_zg_priority"

amovo.ca: Category Archive• Uses the standard custom tax query• Need to ORDER BY wp_postmeta for ALL queries

Filter: posts_clauses• Allows us to manipulate SQL before it is sent to the database• For ALL queries (not just main query) if (! is_admin()){ add_filter( posts_clauses, sort_by_priority, 10, 2 ); } function sort_by_product_priority( $clauses, $query ){ global $wpdb; //… more to come }

Keeping it lean• If query has nothing to do with products, don’t add the overhead• Only affect product-related tax queries function sort_by_product_priority( $clauses, $query ){ global $wpdb; if ( in_array( $query->query_vars[taxonomy], array( product-category, product-application)) ){ // … } }

Make sure its the right query!• These hooks affect EVERY query• Add conditionals to reduce overhead – is_admin() during hook registration – is_main_query() – $query->query_vars (eg: "taxonomy", "post_type", "orderby")if ( page-hijacking == $query_obj->query_vars[pagename]){ … }

JOIN your tables• LEFT JOIN doesnt exclude missing meta• Alias your JOINs to avoid collision function sort_by_product_priority( $clauses, $query ){ global $wpdb; … // JOIN on postmeta to get priority $clauses[join] .= " LEFT JOIN {$wpdb->postmeta} PM ON ({$wpdb->posts}.ID = PM.post_id AND PM.meta_key = _zg_priority) "; … return $clauses; }

Modify ORDER BY• PREPEND your sort criteria• Dont forget to add comma if you need one! function sort_by_product_priority( $clauses, $query ){ … $join .= "LEFT JOIN {$wpdb->postmeta} PM..."; … $orderby = &$clauses[orderby]; // by reference! if (! empty( $orderby ) ) $orderby = , . $orderby; $orderby = " IFNULL(P.meta_value, 5) ASC, {$wpdb->posts}.post_title ASC" . $orderby; return $clauses; }

Manipulating the Main Query (main filters)• Manipulating the URI query variables – before the query is parsed – add_filter( request )• Manipulating the query object – before the SQL is generated – add_filter( parse_query ) / pre_get_posts• Manipulating the SQL – before the SQL is run – add_filter( posts_clauses ) 2 arguments• Manipulating the results – before stickies and status – add_filter( posts_results )

Case Study: Date Range• WP_Query doesnt (currently) support date ranges• Lets create before_date and after_date $date_query = new WP_Query( array( after_date => 2012-08-10, before_date => 2012-08-14 ) );

Exploiting the Query Objectadd_filter( posts_where, date_ranges, 10, 2 );function date_ranges( $where_clause, $query_obj ){ global $wpdb; if ( $before_date = $query_obj->query[before_date] ){ $where_clause .= " AND {$wpdb->posts}.post_date < {$before_date} "; } if ( $after_date = $query_obj->query[after_date] ) ){ $where_clause .= " AND DATE({$wpdb->posts}.post_date) > {$after_date} "; } return $where_clause;}

Improvements & Security• Make sure were actually getting a Date• Cast the time() object to a mySQL DATE string• Cast mySQL TIMESTAMP to DATE portion onlyif ( $after_date = strtotime( $query_obj->query[after_date]) ){ $after_date = date( Y-m-d, $after_date ); $where_clause .= " AND DATE({$wpdb->posts}.post_date) > {$after_date} ";}

Conclusions• TMTOWTDI• Go as high-level as you can• Use query_posts() sparingly• wp_reset_postdata()!• Modify the Main Query with filters / actions• Make WordPress sing!

Working with $wpdb• global $wpdb• Always use $wpdb->table_name• Always use $wpdb->prepare with tainted data• Use the right get_* method for the job – get_var() – get_row() – get_col() – get_results()

Please avoid inserting / updating…• Posts• Users• Meta data (usermeta or postmeta)• Options• Taxonomies and Terms (especially!)• Basically, if theres a default wp_* table, there are core methods for inserting, updating and deleting

When to extend schema• Primary object has tons of metadata• Highly relational data• Plugin tables (be sure to offer DROP option!) – register_deactivation_hook();• Cant map to post, meta and taxonomy

Final observations… n stuff• There are actually very few reasons to generate your own SQL• Theres probably a core function for that• Due diligence and research – Google search "wordpress [keywords]"! – Get a good IDE (Jers talk about NetBeans!)

Thank You!updates: @TomAuger www.tomauger.com

Extra Slides• Ah, time is thy enemy…

More Template Tags<div class="author-info"> <p><strong>Posted by: </strong> <?php the_author(); ?> (<?php the_author_meta( first_name ) ?> <?php the_author_meta( last_name ) ?>) <?php echo apply_filters( the_content, get_the_author_meta( description ) ); ?></div>

Anatomy of a Query• $wp->main() is called after everything is loaded – Parses the browser query string and applies rewrite rules – Rebuilds the query string for main query – Runs get_posts() on the main $wp_the_query (WP_Query instance)• WP_Query then – Reparses the query string • Request for single page short-circuits and uses cache if possible – Parses the search – Parses any taxonomy queries – Generates the SQL clauses – Gives cacheing plugins a chance to get involved – Generates the SQL request and executes it! – Processes comments – Processes stickies – Updates caches

Plugin Authors• Consider require_once( wp-admin/install- helper.php ) within your register_activation_hook() – helper functions like maybe_create_table(), maybe_add_column()

Advanced Post Queries

by TomAuger on Aug 18, 2012

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Advanced Post Queries Presentation Transcript