Merge pull request #686 from coursemology-collab/lowjoel/handle-non-u…

…nique-auto-gradings

Ensure that non-unique auto grading records are properly handled.

app/models/course/assessment/answer.rb

@@ -79,8 +79,10 @@ def validate_consistent_grade
   #
   # @return [Course::Assessment::Answer::AutoGrading]
   def ensure_auto_grading!
-    create_auto_grading! unless auto_grading
-  rescue ActiveRecord::RecordNotUnique
+    auto_grading || create_auto_grading!
+  rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotUnique => e
+    raise e if e.is_a?(ActiveRecord::RecordInvalid) && e.record.errors[:answer_id].empty?
+    association(:auto_grading).reload
     auto_grading
   end
 

spec/models/course/assessment/answer_spec.rb

@@ -176,5 +176,28 @@
         end
       end
     end
+
+    describe '#ensure_auto_grading!' do
+      context 'when an existing auto grading already exists' do
+        let(:existing_record) do
+          # Duplicate the subject so the subject does not know about the grading.
+          create(:course_assessment_answer_auto_grading, answer: subject.class.find(subject.id))
+        end
+
+        it 'returns the existing grading' do
+          # Simulate a concurrent creation of an existing record.
+          expect(subject.auto_grading).to be_nil
+          existing_record
+
+          expect(subject.send(:ensure_auto_grading!)).to eq(existing_record)
+        end
+      end
+
+      context 'when no existing auto grading exists' do
+        it 'creates a new grading' do
+          expect(subject.send(:ensure_auto_grading!)).to be_persisted
+        end
+      end
+    end
   end
 end