Add msm_pre_get_last_modified_posts filter (#178)

README.md

@@ -94,3 +94,19 @@ add_filter( 'msm_sitemap_index', function( $sitemaps ) {
     } );
 } );
 ```
+
+## Filter Sitemap Index
+
+Use the `msm_pre_get_last_modified_posts` filter to customize the query that gets the last modified posts.
+
+On large sites, this filter could be leveraged to enhance query efficiency by avoiding scanning older posts that don't get updated frequently and making better use of the `type_status_date` index.
+
+```
+function ( $query, $post_types_in, $date ) {
+    global $wpdb;
+
+    $query = $wpdb->prepare( "SELECT ID, post_date FROM $wpdb->posts WHERE post_type IN ( {$post_types_in} ) AND post_status = 'publish' AND post_date >= DATE_SUB(NOW(), INTERVAL 3 MONTH) AND post_modified_gmt >= %s LIMIT 1000", $date );
+
+    return $query;
+};
+```

msm-sitemap.php

@@ -615,7 +615,20 @@ public static function get_last_modified_posts() {
 
 		$post_types_in = self::get_supported_post_types_in();
 
-		$modified_posts = $wpdb->get_results( $wpdb->prepare( "SELECT ID, post_date FROM $wpdb->posts WHERE post_type IN ( {$post_types_in} ) AND post_modified_gmt >= %s LIMIT 1000", $date ) );
+		$query = $wpdb->prepare( "SELECT ID, post_date FROM $wpdb->posts WHERE post_type IN ( {$post_types_in} ) AND post_modified_gmt >= %s LIMIT 1000", $date );
+
+		/**
+		 * Filter the query used to get the last modified posts.
+		 * $wpdb->prepare() should be used for security if a new replacement query is created in the callback.
+		 * 
+		 * @param string $query         The query to use to get the last modified posts.
+		 * @param string $post_types_in A comma-separated list of post types to include in the query.
+		 * @param string $date          The date to use as the cutoff for the query.
+		 */
+		$query = apply_filters( 'msm_pre_get_last_modified_posts', $query, $post_types_in, $date );
+
+		$modified_posts = $wpdb->get_results( $query );
+
 		return $modified_posts;
 	}
 

tests/test-sitemap-functions.php

@@ -424,4 +424,48 @@ function add_post_status_to_msm_sitemap( $post_status ) {
 		return 'live';
 	}
 
+	function test_get_last_modified_posts_filter_no_change() {
+		$posts_before = Metro_Sitemap::get_last_modified_posts();
+		$tag          = 'msm_pre_get_last_modified_posts';
+
+		// Test no changes to query.
+		$function = function ( $query ) {
+			return $query;
+		};
+		add_filter( $tag, $function, 10, 3 );
+		$posts_after = Metro_Sitemap::get_last_modified_posts();
+		remove_filter( $tag, $function );
+
+		$this->assertEquals( count( $posts_before ), count( $posts_after ) );
+	}
+
+	function test_get_last_modified_posts_filter_change_query() {
+		$posts_before = Metro_Sitemap::get_last_modified_posts();
+		$tag          = 'msm_pre_get_last_modified_posts';
+
+		// Modify query to fetch posts created in the last 3 months.
+		$function = function ( $query, $post_types_in, $date ) {
+			global $wpdb;
+			$query = $wpdb->prepare( "SELECT ID, post_date FROM $wpdb->posts WHERE post_type IN ( {$post_types_in} ) AND post_date >= DATE_SUB(NOW(), INTERVAL 3 MONTH) AND post_modified_gmt >= %s LIMIT 1000", $date );
+			return $query;
+		};
+
+		add_filter( $tag, $function, 10, 3 );
+		$posts_after_date = Metro_Sitemap::get_last_modified_posts();
+		remove_filter( $tag, $function );
+
+		// Modify query as string to fetch only 10 posts.
+		$limit    = 10;
+		$function = function ( $query ) use ( $limit ) {
+			return str_replace( 'LIMIT 1000', "LIMIT $limit", $query );
+		};
+
+		add_filter( $tag, $function );
+		$posts_after = Metro_Sitemap::get_last_modified_posts();
+		remove_filter( $tag, $function );
+
+		$this->assertLessThan( count( $posts_before ), count( $posts_after_date ) );
+		$this->assertEquals( count( $posts_after ), $limit );
+	}
+
 }