Avoid N+1 queries when fetching events from the API41958-events-performance

3 files changed, 27 insertions, 4 deletions

diff --git a/changelogs/unreleased/41958-events-performance.yml b/changelogs/unreleased/41958-events-performance.yml
new file mode 100644
index 00000000000..bcd52910e62
--- /dev/null
+++ b/changelogs/unreleased/41958-events-performance.yml
@@ -0,0 +1,5 @@
+---
+title: Avoid N+1 queries when fetching events from the API
+merge_request:
+author:
+type: performance
diff --git a/lib/api/events.rb b/lib/api/events.rb
index b0713ff1d54..0787930f363 100644
--- a/lib/api/events.rb
+++ b/lib/api/events.rb
@@ -16,7 +16,7 @@ module API
       end
 
       def present_events(events)
-        events = events.reorder(created_at: params[:sort])
+        events = events.preload(:author, :target, :noteable).reorder(created_at: params[:sort])
 
         present paginate(events), with: Entities::Event
       end
@@ -35,7 +35,7 @@ module API
       get do
         authenticate!
 
-        events = EventsFinder.new(params.merge(source: current_user, current_user: current_user)).execute.preload(:author, :target)
+        events = EventsFinder.new(params.merge(source: current_user, current_user: current_user)).execute
 
         present_events(events)
       end
@@ -58,7 +58,7 @@ module API
         user = find_user(params[:id])
         not_found!('User') unless user
 
-        events = EventsFinder.new(params.merge(source: user, current_user: current_user)).execute.preload(:author, :target)
+        events = EventsFinder.new(params.merge(source: user, current_user: current_user)).execute
 
         present_events(events)
       end
@@ -77,7 +77,7 @@ module API
         use :sort_params
       end
       get ":id/events" do
-        events = EventsFinder.new(params.merge(source: user_project, current_user: current_user)).execute.preload(:author, :target)
+        events = EventsFinder.new(params.merge(source: user_project, current_user: current_user)).execute
 
         present_events(events)
       end
diff --git a/spec/requests/api/events_spec.rb b/spec/requests/api/events_spec.rb
index 962c845f36d..6696fb69273 100644
--- a/spec/requests/api/events_spec.rb
+++ b/spec/requests/api/events_spec.rb
@@ -160,6 +160,24 @@ describe API::Events do
         expect(json_response.size).to eq(1)
       end
 
+      it 'does not perform N+1 queries' do
+        endpoint = api("/projects/#{private_project.id}/events?action=closed", user)
+
+        issue = create(:issue, project: private_project)
+        note = create(:note, project: private_project, noteable: issue)
+        create(:event, project:private_project, target: note, action: Event::CLOSED)
+
+        control_count = ActiveRecord::QueryRecorder.new { get endpoint }.count
+
+        issues = create_list(:issue, 5, project: private_project)
+        issues.each do |issue|
+          note = create(:note, project: private_project, noteable: issue)
+          create(:event, project:private_project, target: note, action: Event::CLOSED)
+        end
+
+        expect { get endpoint }.not_to exceed_query_limit(control_count)
+      end
+
       it 'returns 404 if project does not exist' do
         get api("/projects/1234/events", user)