Perf: Better response times from api/public/v1/courses

app/controllers/api/public/v1/courses_controller.rb

@@ -7,24 +7,36 @@ class CoursesController < API::Public::V1::ApplicationController
         def index
           render jsonapi: paginate(courses),
                  include: include_param,
-                 meta: { count: courses.count('course.id') },
+                 meta: { count: cached_course_count },
                  class: API::Public::V1::SerializerService.call
         rescue ActiveRecord::StatementInvalid
           render json: { status: 400, message: 'Invalid changed_since value, the format should be an ISO8601 UTC timestamp, for example: `2019-01-01T12:01:00Z`' }.to_json, status: :bad_request
         end
 
         private
 
+        def cached_course_count
+          year = permitted_params[:recruitment_cycle_year] || RecruitmentCycle.current.year
+
+          Rails.cache.fetch("api_course_count_#{year}", expires_in: 5.minutes) do
+            courses.count('course.id')
+          end
+        end
+
         def courses
           @courses ||= APICourseSearchService.call(
-            filter: params[:filter],
-            sort: params[:sort],
+            filter: permitted_params[:filter],
+            sort: permitted_params[:sort],
             course_scope: recruitment_cycle.courses
           )
         end
 
         def include_param
-          params.fetch(:include, '')
+          permitted_params.fetch(:include, '')
+        end
+
+        def permitted_params
+          params.permit('page', 'sort', 'per_page', 'courses', 'recruitment_cycle_year', 'include', 'filter' => %w[updated_since funding_type])
         end
       end
     end

app/models/course.rb

@@ -585,6 +585,8 @@ def gcse_grade_required
   end
 
   def last_published_at
+    return enrichments.select(&:last_published_timestamp_utc).max_by(&:last_published_timestamp_utc)&.last_published_timestamp_utc if enrichments.loaded?
+
     enrichments.maximum(:last_published_timestamp_utc)
   end
 

app/models/required_qualifications_summary.rb

@@ -8,7 +8,11 @@ def initialize(course)
   end
 
   def extract
-    legacy_qualifications_attribute = course.latest_published_enrichment&.required_qualifications
+    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

app/serializers/api/public/v1/serializable_course.rb

@@ -134,7 +134,7 @@ def enrichment_attribute(name, enrichment_name = name)
         end
 
         attribute :subject_codes do
-          @object.subjects.pluck(:subject_code).compact
+          @object.subjects.map(&:subject_code).compact
         end
 
         attribute :required_qualifications do

spec/controllers/api/public/v1/courses_controller_spec.rb

@@ -262,7 +262,7 @@
 
           it 'delegates to the CourseSearchService' do
             expect(CourseSearchService).to have_received(:call).with(
-              hash_including(filter: ActionController::Parameters.new(funding_type: 'salary'))
+              hash_including(filter: ActionController::Parameters.new(funding_type: 'salary').permit!)
             )
           end
         end

spec/models/course_spec.rb

@@ -3157,6 +3157,38 @@
     end
   end
 
+  describe '#last_published_at' do
+    context 'with an unpublished course' do
+      let(:course) { create(:course, study_mode: :part_time, enrichments: [create(:course_enrichment)]) }
+
+      it 'returns nil' do
+        expect(course.last_published_at).to be_nil
+      end
+    end
+
+    context 'with a twice published course' do
+      let(:course) do
+        create(:course, study_mode: :part_time, enrichments:
+          [
+            create(:course_enrichment, :published, last_published_timestamp_utc: '1/1/2024'),
+            create(:course_enrichment, :published, last_published_timestamp_utc: '1/1/2023')
+          ])
+      end
+
+      it 'selects the enrichment with the latest date' do
+        expect(course.last_published_at).to eq('1/1/2024')
+      end
+
+      context 'when the enrichments are not loaded' do
+        it 'selects the enrichment with the latest date' do
+          course.reload
+          expect(course.enrichments.loaded?).to be_falsey
+          expect(course.last_published_at).to eq('1/1/2024')
+        end
+      end
+    end
+  end
+
   describe 'funding_type and program_type' do
     context 'setting the funding to apprenticeship' do
       it 'sets the funding to apprenticeship and program_type to pg_teaching_apprenticeship' do

spec/models/required_qualifications_summary_spec.rb

@@ -14,6 +14,18 @@
       end
     end
 
+    context 'when the course enrichments are not loaded' do
+      let(:enrichment) { build(:course_enrichment, :published, required_qualifications: 'GCSE Computer Science') }
+      let(:course) { create(:course, enrichments: [enrichment]) }
+
+      it 'returns the expected value' do
+        course.reload
+        expect(course.enrichments.loaded?).to be_falsey
+        summary = described_class.new(course).extract
+        expect(summary).to eq 'GCSE Computer Science'
+      end
+    end
+
     context 'when required_qualifications enrichment attribute is blank' do
       it 'assembles a whole summary based on course attributes' do
         course = create(:course, :primary)