WordCamp Chicago developer track talk on "URL to SQL to HTML", explaining how WordPress URL parsing and content selection works.

1. Parsing Strange:URL to SQL to HTML Hal Stern http://snowmanonfire.com headshot by Richard Stevenshttp://dieselsweeties.com

2. Why Do You Care? Database performance = user experience A little database expertise goes a long way Use taxonomies for more than sidebar lists WordPress is a powerful CMS Change default behaviors Defy the common wisdom Integrate other content sources/filters WordCamp Chicago 2

3. Disclaimers I’m somewhat social, for Jersey I’m (old) old school If using PHP echo gives you hives……take a Benadryl now If “INNER JOIN” makes you giggle, you’re in the wrong session/conference/fantasy I suck at art and design 3 WordCamp Chicago

4. Flow of Control Web server URL manipulation Real file or permalink URL? URL to query variables What to display? Tag? Post? Category? Query variables to SQL generation How exactly to get that content? Template file selection How will content be displayed? Content manipulation 4 WordCamp Chicago

5. Whose File Is This? User URL request passed to web server Web server checks.htaccessfile WP install root Other .htaccessfiles may interfere Basic rewriting rules:If file or directory URL doesn’t exist, start WordPress via index.php WordCamp Chicago 5 <IfModulemod_rewrite.c> RewriteEngine On RewriteBase /whereyouputWordPress/ RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule . /index.php [L] </IfModule>

6. What Happens Before The Loop Parse URL into a query Set conditionals & select templates Execute the query & cache results Run the Loop:<?phpif (have_posts()) : while (have_posts()) : the_post(); //loop contentendwhile;endif;?> WordCamp Chicago 6

7. Examining the Query String SQL passed to MySQL in WP_Query object’s request element Brute force: edit theme footer.phpto see main loop’s query for displayed page WordCamp Chicago 7 <?php global $wp_query; echo ”SQL for this page "; echo $wp_query->request; echo "<br>"; ?>

8. SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.post_type = 'post’ AND(wp_posts.post_status = 'publish' ORwp_posts.post_status = 'private’)ORDER BY wp_posts.post_date DESC LIMIT 0, 10 “Home Page” Query Deconstruction WordCamp Chicago 8 Get all fields from posts table, but limit number of returned rows Only get posts, and those that are published or private to the user Sort the results by date in descending order Start results starting with record 0 and up to 10 more results

9. Query Parsing parse_request() method of WP_Query extracts query variables from URL Execute rewrite rules Pick off ?p=67 style http GET variables Match permalink structure Match keywords like “author” and “tag” WordCamp Chicago 9

10. Query Variables to SQL Query type: post by title, posts by category or tag, posts by date Variables for the query Slug values for category/tags Month/day numbers Explicit variable values?p=67 for post_id WordCamp Chicago 10

11. Simple Title Slug Parsing Rewrite matches root of permalink, extracts tail of URL as a title slug WordCamp Chicago 11 /2010/premio-sausage SELECT wp_posts.* FROM wp_posts WHERE 1=1 AND YEAR(wp_posts.post_date)='2010' AND wp_posts.post_name = 'premio-sausage' AND wp_posts.post_type = 'post' ORDER BY wp_posts.post_date DESC

12. Graphs and JOIN Operations WordPress treats tags and categories as “terms”, mapped 1:N to posts Relational databases aren’t ideal for this INNER JOIN builds intermediate tables on common key values Following link in a social graph is equivalent to an INNER JOIN on tables of linked items WordCamp Chicago 12

13. WordPress Taxonomy Tables Term relationships table maps N:1 terms to each post Term taxonomy maps slugs 1:N to taxonomies Term table has slugs for URL mapping WordCamp Chicago 13 wp_term_relationshipsobject_idterm_taxonomy_id wp_postspost_id….post_date… post_content wp_term_taxonomyterm_taxonomy_idterm_idtaxonomydescription wp_terms term_idnameslug

14. SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_postsINNER JOIN wp_term_relationships ON(wp_posts.ID = wp_term_relationships.object_id)INNER JOIN wp_term_taxonomy ON (wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id)INNER JOIN wp_terms ON (wp_term_taxonomy.term_id = wp_terms.term_id)WHERE 1=1 AND wp_term_taxonomy.taxonomy = 'post_tag' AND wp_terms.slug IN ('premio') AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 10 Taxonomy Lookup WordCamp Chicago 14 /tag/premio

15. More on Canonical URLs Canonical URLs improve SEO WordPress is really good about generating 301 Redirects for non-standard URLs Example: URL doesn’t appear to match a permalink, WordPress does prediction Use “LIKE title%” in WHERE clause Matches “title” as initial substring with % wildcard WordCamp Chicago 15

16. Modifying the Query Brute force isn’t necessarily good Using query_posts() ignores all previous parsing, runs a new SQL query Filter query_vars Change default parsing (convert any day to a week’s worth of posts, for example) Actions parse_query & parse_request Access WP_Query object before execution is_xx() conditionals are already set WordCamp Chicago 16

17. SQL Generation Filters posts_where More explicit control over query variable to SQL grammar mapping posts_join Add or modify JOINS for other graph like relationships Many other filters Change grouping of results Change ordering of results WordCamp Chicago 17

18. Applications Stylized listings Category sorted alphabetically Use posts as listings of resources (jobs, clients, events) Custom URL slugs Add rewrite rules to match slug and set query variables Joining other social graphs Suggested/related content WordCamp Chicago 18

19. Template File Selection is_x() conditionals set in query parsing Used to drive template selection is_tag() looks for tag-slug, tag-id, then tag Full search hierarchy in Codex template_redirectaction Called in the template loader Add actions to override defaults WordCamp Chicago 19

20. HTML Generation Done in the_post() method Raw content retrieved from MySQL Short codes interpreted CSS applied Some caching plugins generate and store HTML, so YMMV WordCamp Chicago 20

21. Why Do You Care? User experience improvement JOINS are expensive Large table, repetitive SELECTs = slow Running query once keeps cache warm Category, permalink, title slug choices matter More CMS, less “blog” Alphabetical sort Adding taxonomy/social graph elements WordCamp Chicago 21

22. Blunt Self-Promotion Brad and David are here, too They’re significantly more WP literate than me This slide was more helpful yesterday 22 WordCamp Chicago

23. Resources Core files where SQL stuff happens query.php post.php canonical.php Template loader search path http://codex.wordpress.org/Template_Hierarchy WordCamp Chicago 23

24. Contact Hal Stern freeholdhal@gmail.com @freeholdhal http://snowmanonfire.com http://facebook.com/hal.stern http://slideshare.net/freeholdhal WordCamp Chicago 24