Quick changes to clean up api using serializer save

apps/submissions/api.py

@@ -137,13 +137,16 @@ def create_submission(student_item_dict, answer, submitted_at=None,
         model_kwargs["submitted_at"] = submitted_at
 
     try:
+        # Serializer validation requires the student item primary key, rather
+        # than the student item model itself. Create a copy of the submission
+        # kwargs and replace the student item model with it's primary key.
         validation_data = model_kwargs.copy()
         validation_data["student_item"] = student_item_model.pk
         submission_serializer = SubmissionSerializer(data=validation_data)
-        submission_serializer.is_valid()
-        if submission_serializer.errors:
+        if not submission_serializer.is_valid():
             raise SubmissionRequestError(submission_serializer.errors)
-        submission = Submission.objects.create(**model_kwargs)
+        submission_serializer.save()
+        return submission_serializer.data
     except DatabaseError:
         error_message = u"An error occurred while creating submission {} for student item: {}".format(
             model_kwargs,
@@ -152,8 +155,6 @@ def create_submission(student_item_dict, answer, submitted_at=None,
         logger.exception(error_message)
         raise SubmissionInternalError(error_message)
 
-    return SubmissionSerializer(submission).data
-
 
 def get_submissions(student_item_dict, limit=None):
     """Retrieves the submissions for the specified student item,
@@ -264,17 +265,14 @@ def _get_or_create_student_item(student_item_dict):
     """
     try:
         try:
-            student_item_model = StudentItem.objects.get(**student_item_dict)
+            return StudentItem.objects.get(**student_item_dict)
         except StudentItem.DoesNotExist:
-            student_item_serializer = StudentItemSerializer(
-                data=student_item_dict)
-            student_item_serializer.is_valid()
-            if student_item_serializer.errors:
+            student_item_serializer = StudentItemSerializer(data=student_item_dict)
+            if not student_item_serializer.is_valid():
                 raise SubmissionRequestError(student_item_serializer.errors)
-            student_item_model = StudentItem.objects.create(**student_item_dict)
+            return student_item_serializer.save()
     except DatabaseError:
         error_message = u"An error occurred creating student item: {}".format(
             student_item_dict)
         logger.exception(error_message)
         raise SubmissionInternalError(error_message)
-    return student_item_model

apps/submissions/tests/test_api.py

@@ -7,7 +7,8 @@ from nose.tools import raises
 from mock import patch
 
 from submissions.api import create_submission, get_submissions, SubmissionRequestError, SubmissionInternalError
-from submissions.models import Submission, StudentItem
+from submissions.models import Submission
+from submissions.serializers import StudentItemSerializer
 
 STUDENT_ITEM = dict(
     student_id="Tim",
@@ -73,10 +74,10 @@ class TestApi(TestCase):
         mock_filter.side_effect = DatabaseError("Bad things happened")
         create_submission(STUDENT_ITEM, ANSWER_ONE)
 
-    @patch.object(StudentItem.objects, 'create')
+    @patch.object(StudentItemSerializer, 'save')
     @raises(SubmissionInternalError)
-    def test_create_student_item_validation(self, mock_create):
-        mock_create.side_effect = DatabaseError("Bad things happened")
+    def test_create_student_item_validation(self, mock_save):
+        mock_save.side_effect = DatabaseError("Bad things happened")
         create_submission(STUDENT_ITEM, ANSWER_ONE)
 
     def test_unicode_enforcement(self):