The posts_join Hook in WPFTS

The posts_join hook in WordPress is a filter that allows modification of the SQL JOIN clause used to combine tables in a query. WPFTS uses this hook to join the posts table (wp_posts) with a temporary table containing post relevance information calculated by the plugin’s search engine.

What WPFTS Does When posts_join is Called:

1. Checks for Indexed Search Usage: The plugin checks if indexed search is enabled in WPFTS ($wpq->wpftsi_session['use_indexed_search']).
2. Adds JOIN with Temporary Table: If indexed search is enabled, WPFTS adds a JOIN with a temporary table (aliased as wpfts_t), which contains post IDs and their relevance scores. This allows retrieving the relevance score for each post in the search results.

Important Functions Involved in posts_join Handling:

• WPFTS_Search::index_sql_joins()

How to Use This in Addon Development:

Addon developers need to be aware that WPFTS might add its own JOINs to the SQL query. If your addon also uses JOINs, ensure your logic doesn’t conflict with WPFTS.

Additional Notes:

• WPFTS only adds the JOIN when indexed search is used.
• The temporary relevance table is created in the WPFTS_Search::sql_parts() method.
• This hook demonstrates how WPFTS integrates its search engine with WordPress at the SQL query level.