From 0d446ef015ddec29fcaddbd65a5db169a42cfd53 Mon Sep 17 00:00:00 2001
From: Iain McNulty <iain.mcnulty@education.gov.uk>
Date: Fri, 25 Oct 2024 16:54:01 +0100
Subject: [PATCH] Reduce number of queries in the courses api

---
 app/models/course.rb                                 | 2 ++
 app/models/required_qualifications_summary.rb        | 7 ++++++-
 app/serializers/api/public/v1/serializable_course.rb | 2 +-
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/app/models/course.rb b/app/models/course.rb
index c3894c5035..105803454d 100644
--- a/app/models/course.rb
+++ b/app/models/course.rb
@@ -585,6 +585,8 @@ def gcse_grade_required
   end
 
   def last_published_at
+    return enrichments.max_by(&:last_published_timestamp_utc).last_published_timestamp_utc if enrichments.loaded?
+
     enrichments.maximum(:last_published_timestamp_utc)
   end
 
diff --git a/app/models/required_qualifications_summary.rb b/app/models/required_qualifications_summary.rb
index ed68511a53..1031d88829 100644
--- a/app/models/required_qualifications_summary.rb
+++ b/app/models/required_qualifications_summary.rb
@@ -8,7 +8,12 @@ def initialize(course)
   end
 
   def extract
-    legacy_qualifications_attribute = course.latest_published_enrichment&.required_qualifications
+    # This performance improvement saves ~100 database queries in the courses api endpoint
+    legacy_qualifications_attribute = if course.enrichments.loaded?
+                                        course.enrichments.max_by(&:created_at)&.required_qualifications
+                                      else
+                                        course.latest_published_enrichment&.required_qualifications
+                                      end
     return legacy_qualifications_attribute if legacy_qualifications_attribute.present?
 
     generate_summary_text
diff --git a/app/serializers/api/public/v1/serializable_course.rb b/app/serializers/api/public/v1/serializable_course.rb
index d0d0b64956..8b0e7d2484 100644
--- a/app/serializers/api/public/v1/serializable_course.rb
+++ b/app/serializers/api/public/v1/serializable_course.rb
@@ -11,7 +11,7 @@ class SerializableCourse < JSONAPI::Serializable::Resource
         class << self
           def enrichment_attribute(name, enrichment_name = name)
             attribute name do
-              @object.latest_published_enrichment&.public_send(enrichment_name)
+              @object.enrichments.max_by(&:created_at)&.public_send(enrichment_name)
             end
           end
         end