update comment count in post trigger

replaceable_schema.sql

@@ -202,7 +202,8 @@ CALL r.post_or_comment ('post');
 
 CALL r.post_or_comment ('comment');
 
--- Create triggers that update counts in parent aggregates
+-- Create triggers that update counts in parent aggregates (a trigger can run in response to deletion caused by
+-- a foreign key with `ON DELETE CASCADE`, so the parent might not exist)
 CALL r.create_triggers ('comment', $$ WITH comment_group AS (
         SELECT
             (comment).post_id,
@@ -287,7 +288,8 @@ unused_person_aggregates_update_result AS (
 
 CALL r.create_triggers ('post', $$ WITH post_group AS (
         SELECT
-            (post).community_id, (post).creator_id, (post).local, coalesce(sum(count_diff), 0) AS posts FROM combined_transition_tables
+            (post).community_id, (post).creator_id, (post).local, coalesce(sum(count_diff), 0) AS posts,
+            coalesce(sum(count_diff * (SELECT comments FROM post_aggregates WHERE post_id = (post).id LIMIT 1)), 0) AS comments FROM combined_transition_tables
             WHERE
                 NOT ((post).deleted
                 OR (post).removed)
@@ -307,7 +309,9 @@ CALL r.create_triggers ('post', $$ WITH post_group AS (
     UPDATE
         community_aggregates AS a
     SET
-        posts = a.posts + post_group.posts FROM post_group
+        posts = a.posts + post_group.posts,
+        -- Update comment count when post is deleted, removed, or restored
+        comments = a.comments + post_group.comments FROM post_group
         WHERE
             a.community_id = post_group.community_id $$);
 
@@ -329,53 +333,6 @@ CALL r.create_triggers ('person', $$ UPDATE
                 coalesce(sum(count_diff), 0) AS users FROM combined_transition_tables
             WHERE (person).local) AS diff $$);
 
--- For community_aggregates.comments, don't include comments of deleted or removed posts
-CREATE FUNCTION r.update_comment_count_from_post ()
-    RETURNS TRIGGER
-    LANGUAGE plpgsql
-    AS $$
-BEGIN
-    UPDATE
-        community_aggregates AS a
-    SET
-        comments = a.comments + diff.comments
-    FROM (
-        SELECT
-            old_post.community_id,
-            sum((
-                CASE WHEN new_post.deleted
-                    AND new_post.removed THEN
-                    -1
-                ELSE
-                    1
-                END) * post_aggregates.comments) AS comments
-        FROM
-            new_post
-            INNER JOIN old_post ON new_post.id = old_post.id
-                AND (new_post.deleted
-                    AND new_post.removed) != (old_post.deleted
-                    AND old_post.removed),
-                LATERAL (
-                    SELECT
-                        *
-                    FROM
-                        post_aggregates
-                WHERE
-                    post_id = new_post.id
-                LIMIT 1) AS post_aggregates
-        GROUP BY
-            old_post.community_id) AS diff
-WHERE
-    a.community_id = diff.community_id;
-    RETURN NULL;
-END
-$$;
-
-CREATE TRIGGER comment_count
-    AFTER UPDATE ON post REFERENCING OLD TABLE AS old_post NEW TABLE AS new_post
-    FOR EACH STATEMENT
-    EXECUTE FUNCTION r.update_comment_count_from_post ();
-
 -- Count subscribers for local communities
 CALL r.create_triggers ('community_follower', $$ UPDATE
         community_aggregates AS a