Invalidate query transients to avoid cache flush

Part of #5777. These transients are required and cannot be predicted.

If not using an external cache system, the DB is cleared still to keep
size down after invalidation.

For these 2 transients, invalidation occurs when visibility altering
product attributes are edited.

includes/class-wc-cache-helper.php

@@ -23,6 +23,37 @@ class WC_Cache_Helper {
 		add_action( 'admin_notices', array( __CLASS__, 'notices' ) );
 	}
 
+	/**
+	 * Get transient version
+	 *
+	 * When using transients with unpredictable names, e.g. those containing an md5 
+	 * hash in the name, we need a way to invalidate them all at once. 
+	 *
+	 * When using default WP transients we're able to do this with a DB query to 
+	 * delete transients manually.
+	 *
+	 * With external cache however, this isn't possible. Instead, this function is used
+	 * to append a unique string (based on time()) to each transient. When transients 
+	 * are invalidated, the transient version will increment and data will be regenerated.
+	 *
+	 * Raised in issue https://github.com/woothemes/woocommerce/issues/5777
+	 * Adapted from ideas in http://tollmanz.com/invalidation-schemes/
+	 * 
+	 * @param  string  $group   Name for the group of transients we need to invalidate
+	 * @param  boolean $refresh true to force a new version
+	 * @return string transient version based on time(), 10 digits
+	 */
+	public static function get_transient_version( $group, $refresh = false ) {
+		$transient_name  = $group . '-transient-version';
+		$transient_value = get_transient( $key );
+
+		if ( false === $transient_value || true === $refresh ) {
+			$transient_value = time();
+			set_transient( $transient_name, $transient_value );
+		}
+		return $transient_value;
+	}
+
 	/**
 	 * Prevent caching on dynamic pages.
 	 *

includes/class-wc-post-data.php

@@ -59,15 +59,21 @@ class WC_Post_Data {
 	 * Delete product view transients when needed e.g. when post status changes, or visibility/stock status is modified.
 	 */
 	public static function delete_product_query_transients() {
+		// Increments the transient version to invalidate cache
+		WC_Cache_Helper::get_transient_version( 'product_query', true );
+
+		// If not using an external caching system, we can clear the transients out manually and avoid filling our DB
+		if ( ! wp_using_ext_object_cache() ) {
 			global $wpdb;
 
-		if ( wp_using_ext_object_cache() ) {
-			wp_cache_flush(); // There isn't a reliable method of looking up the names, so flush the cache.
-			return;
+			$wpdb->query( "
+				DELETE FROM `$wpdb->options` 
+				WHERE `option_name` LIKE ('\_transient\_wc\_uf\_pid\_%') 
+				OR `option_name` LIKE ('\_transient\_timeout\_wc\_uf\_pid\_%')
+				OR `option_name` LIKE ('\_transient\_wc\_products\_will\_display\_%')
+				OR `option_name` LIKE ('\_transient\_timeout\_wc\_products\_will\_display\_%')
+			" );
 		}
-
-		$wpdb->query( "DELETE FROM `$wpdb->options` WHERE `option_name` LIKE ('\_transient\_wc\_uf\_pid\_%') OR `option_name` LIKE ('\_transient\_timeout\_wc\_uf\_pid\_%')" );
-		$wpdb->query( "DELETE FROM `$wpdb->options` WHERE `option_name` LIKE ('\_transient\_wc\_products\_will\_display\_%') OR `option_name` LIKE ('\_transient\_timeout\_wc\_products\_will\_display\_%')" );
 	}
 
 	/**

includes/class-wc-query.php

@@ -435,7 +435,7 @@ class WC_Query {
 		unset( $current_wp_query['paged'] );
 
 		// Generate a transient name based on current query
-		$transient_name = 'wc_uf_pid_' . md5( http_build_query( $current_wp_query ) );
+		$transient_name = 'wc_uf_pid_' . md5( http_build_query( $current_wp_query ) . WC_Cache_Helper::get_transient_version( 'product_query' ) );
 		$transient_name = ( is_search() ) ? $transient_name . '_s' : $transient_name;
 
 		if ( false === ( $unfiltered_product_ids = get_transient( $transient_name ) ) ) {
@@ -464,17 +464,19 @@ class WC_Query {
 		$this->unfiltered_product_ids = $unfiltered_product_ids;
 
 		// Also store filtered posts ids...
-		if ( sizeof( $this->post__in ) > 0 )
+		if ( sizeof( $this->post__in ) > 0 ) {
 			$this->filtered_product_ids = array_intersect( $this->unfiltered_product_ids, $this->post__in );
-		else
+		} else {
 			$this->filtered_product_ids = $this->unfiltered_product_ids;
+		}
 
 		// And filtered post ids which just take layered nav into consideration (to find max price in the price widget)
-		if ( sizeof( $this->layered_nav_post__in ) > 0 )
+		if ( sizeof( $this->layered_nav_post__in ) > 0 ) {
 			$this->layered_nav_product_ids = array_intersect( $this->unfiltered_product_ids, $this->layered_nav_post__in );
-		else
+		} else {
 			$this->layered_nav_product_ids = $this->unfiltered_product_ids;
 		}
+	}
 
 
 	/**

includes/wc-template-functions.php

@@ -1340,7 +1340,9 @@ if ( ! function_exists( 'woocommerce_products_will_display' ) ) {
 			return true;
 		}
 
-		if ( false === ( $products_will_display = get_transient( 'wc_products_will_display_' . $parent_id ) ) ) {
+		$transient_name = 'wc_products_will_display_' . $parent_id . WC_Cache_Helper::get_transient_version( 'product_query' );
+
+		if ( false === ( $products_will_display = get_transient( $transient_name ) ) ) {
 			$has_children = $wpdb->get_col( $wpdb->prepare( "SELECT term_id FROM {$wpdb->term_taxonomy} WHERE parent = %d AND taxonomy = %s", $parent_id, $taxonomy ) );
 
 			if ( $has_children ) {
@@ -1363,7 +1365,7 @@ if ( ! function_exists( 'woocommerce_products_will_display' ) ) {
 			}
 		}
 
-		set_transient( 'wc_products_will_display_' . $parent_id, $products_will_display, YEAR_IN_SECONDS );
+		set_transient( $transient_name, $products_will_display, YEAR_IN_SECONDS );
 
 		return $products_will_display;
 	}