Performance: Only update specific calendars on destroy and not loop over all.

app/models/calendar.rb

@@ -373,18 +373,14 @@ returns
     end
 
     # check if sla's are refer to an existing calendar
-    default_calendar = Calendar.find_by(default: true)
-    Sla.find_each do |sla|
-      if !sla.calendar_id
-        sla.calendar_id = default_calendar.id
-        sla.save!
-        next
-      end
-      if !Calendar.exists?(id: sla.calendar_id)
+    if destroyed?
+      default_calendar = Calendar.find_by(default: true)
+      Sla.where(calendar_id: id).find_each do |sla|
         sla.calendar_id = default_calendar.id
         sla.save!
       end
     end
+
     true
   end
 

spec/models/calendar_spec.rb

@@ -43,6 +43,19 @@ RSpec.describe Calendar, type: :model do
           expect { described_class.first.destroy }
             .to change { calendar.reload.default }.to(true)
         end
+
+        context 'when sla has destroyed calendar set' do
+          let(:sla) { create(:sla, calendar: described_class.first) }
+
+          before do
+            sla
+          end
+
+          it 'sets the new default calendar to the sla' do
+            expect { described_class.first.destroy }
+              .to change { sla.reload.calendar }.to(calendar)
+          end
+        end
       end
     end