Notify Router only on specific column updates

Currently, we send a notification to the Router to update route tables
whenever there is any change to the content_items (or publish_intents)
tables. However, the Router only needs to update the route table when
changes affect specific columns that determine the routes.

This change should reduce unnecessary reloading.

db/migrate/20241209132444_update_notify_trigger_for_route_changes.rb

@@ -0,0 +1,38 @@
+class UpdateNotifyTriggerForRouteChanges < ActiveRecord::Migration[7.2]
+  def up
+    execute <<-SQL
+      CREATE OR REPLACE FUNCTION notify_route_change() RETURNS trigger AS $$
+      BEGIN
+          -- Trigger on INSERT or DELETE
+          IF (TG_OP = 'INSERT' OR TG_OP = 'DELETE') THEN
+              PERFORM pg_notify('route_changes', '');
+              RETURN COALESCE(NEW, OLD);
+          END IF;
+
+          -- Trigger on UPDATE for specific columns
+          IF (TG_OP = 'UPDATE') THEN
+              IF (NEW.routes IS DISTINCT FROM OLD.routes OR
+                  NEW.redirects IS DISTINCT FROM OLD.redirects OR
+                  NEW.schema_name IS DISTINCT FROM OLD.schema_name OR
+                  NEW.rendering_app IS DISTINCT FROM OLD.rendering_app) THEN
+                  PERFORM pg_notify('route_changes', '');
+              END IF;
+          END IF;
+
+          RETURN COALESCE(NEW, OLD);
+      END;
+      $$ LANGUAGE plpgsql;
+    SQL
+  end
+
+  def down
+    execute <<-SQL
+      CREATE OR REPLACE FUNCTION notify_route_change() RETURNS trigger AS $$
+      BEGIN
+        PERFORM pg_notify('route_changes', '');
+        RETURN OLD;
+      END;
+      $$ LANGUAGE plpgsql;
+    SQL
+  end
+end

db/structure.sql

@@ -52,8 +52,23 @@ CREATE FUNCTION public.notify_route_change() RETURNS trigger
     LANGUAGE plpgsql
     AS $$
       BEGIN
-        PERFORM pg_notify('route_changes', '');
-        RETURN OLD;
+          -- Trigger on INSERT or DELETE
+          IF (TG_OP = 'INSERT' OR TG_OP = 'DELETE') THEN
+              PERFORM pg_notify('route_changes', '');
+              RETURN COALESCE(NEW, OLD);
+          END IF;
+
+          -- Trigger on UPDATE for specific columns
+          IF (TG_OP = 'UPDATE') THEN
+              IF (NEW.routes IS DISTINCT FROM OLD.routes OR
+                  NEW.redirects IS DISTINCT FROM OLD.redirects OR
+                  NEW.schema_name IS DISTINCT FROM OLD.schema_name OR
+                  NEW.rendering_app IS DISTINCT FROM OLD.rendering_app) THEN
+                  PERFORM pg_notify('route_changes', '');
+              END IF;
+          END IF;
+
+          RETURN COALESCE(NEW, OLD);
       END;
       $$;
 
@@ -437,6 +452,7 @@ CREATE TRIGGER publish_intent_change_trigger AFTER INSERT OR DELETE OR UPDATE ON
 SET search_path TO "$user", public;
 
 INSERT INTO "schema_migrations" (version) VALUES
+('20241209132444'),
 ('20241105135438'),
 ('20240312132747'),
 ('20240220151333'),

spec/integration/notify_route_change_spec.rb

@@ -39,7 +39,7 @@ def postgres_listener(channel)
     content_item = create(:content_item)
 
     listener = postgres_listener("route_changes")
-    content_item.update!(base_path: "/foo")
+    content_item.update!(schema_name: "gone")
 
     expect(listener.pop).to eq("route_changes")
   end
@@ -62,7 +62,7 @@ def postgres_listener(channel)
   it "sends a notification when publish intent updated" do
     publish_intent = create(:publish_intent)
     listener = postgres_listener("route_changes")
-    publish_intent.update!(publish_time: 10.minutes.from_now)
+    publish_intent.update!(rendering_app: "updated")
 
     expect(listener.pop).to eq("route_changes")
   end