From 337ae5314152bc631f19598694aeef139fb6fce7 Mon Sep 17 00:00:00 2001
From: "Karl O. Pinc kop@karlpinc.com" <kop@karlpinc.com>
Date: Thu, 2 Oct 2025 22:13:46 +0000
Subject: [PATCH] Enforce rule that a follow must have a related
 FOLLOW_OBSERVERS row

---
 db/schemas/lib/triggers/create/follows.m4 | 44 +++++++++++++++++++++++
 db/schemas/lib/triggers/drop/follows.m4   |  1 +
 2 files changed, 45 insertions(+)

diff --git a/db/schemas/lib/triggers/create/follows.m4 b/db/schemas/lib/triggers/create/follows.m4
index 1c476a0..19c7100 100644
--- a/db/schemas/lib/triggers/create/follows.m4
+++ b/db/schemas/lib/triggers/create/follows.m4
@@ -103,8 +103,52 @@ CREATE OR REPLACE FUNCTION follows_func ()
 $$;
 
 
+RAISE INFO 'follows_commit_func';
+CREATE OR REPLACE FUNCTION follows_commit_func ()
+  RETURNS trigger
+  LANGUAGE plpgsql
+  sdb_function_set_search_path
+  AS $$
+  BEGIN
+  -- Function for follows insert trigger fired on transaction commit
+  --
+  -- AGPL_notice(`  --', `2025',
+                 `The Meme Factory, Inc., www.karlpinc.com')
+
+  -- A row must exist on FOLLOW_OBSERVERS
+  PERFORM 1
+    FROM follow_observers
+    WHERE follow_observers.fid = NEW.fid;
+  IF NOT FOUND THEN
+    RAISE EXCEPTION integrity_constraint_violation USING
+          MESSAGE = 'Error on INSERT of FOLLOWS'
+        , DETAIL = 'A row on FOLLOWS must have a related row on'
+                   || ' FOLLOW_OBSERVERS'
+                   || ': Key (FID) = ('
+                   || NEW.fid
+                   || '), Value (Focal) = ('
+                   || NEW.focal
+                   || '), Value (Date) = ('
+                   || NEW.Date
+                   || '), Value (Community) = ('
+                   || NEW.community
+                   || ')';
+  END IF;
+
+  RETURN NULL;
+  END;
+$$;
+
 RAISE INFO 'follows_trigger';
 CREATE TRIGGER follows_trigger
   AFTER INSERT OR UPDATE
   ON follows FOR EACH ROW
   EXECUTE PROCEDURE follows_func();
+
+RAISE INFO 'follows_commit_trigger';
+CREATE CONSTRAINT TRIGGER follows_commit_trigger
+  AFTER INSERT
+  ON follows
+  DEFERRABLE INITIALLY DEFERRED
+  FOR EACH ROW
+  EXECUTE PROCEDURE follows_commit_func();
diff --git a/db/schemas/lib/triggers/drop/follows.m4 b/db/schemas/lib/triggers/drop/follows.m4
index 3017808..06ecd58 100644
--- a/db/schemas/lib/triggers/drop/follows.m4
+++ b/db/schemas/lib/triggers/drop/follows.m4
@@ -21,3 +21,4 @@ dnl m4 includes
 include(`copyright.m4')dnl
 
 DROP FUNCTION IF EXISTS follows_func() CASCADE;
+DROP FUNCTION IF EXISTS follows_commit_func() CASCADE;
-- 
2.34.1