student-results-migration: Migrate data stored in the `student_results` field

Format change broke backward-compatibility with the previous data format.
Changed `completed` to `status` in `self.student_results` to accomodate
partial responses.

mentoring/mentoring.py

@@ -39,7 +39,6 @@ from xblock.fragment import Fragment
 from .light_children import XBlockWithLightChildren
 from .title import TitleBlock
 from .header import SharedHeaderBlock
-from .html import HTMLBlock
 from .message import MentoringMessageBlock
 from .step import StepParentMixin
 from .utils import loader
@@ -142,6 +141,9 @@ class MentoringBlock(XBlockWithLightChildren, StepParentMixin):
         return Score(score, int(round(score * 100)), correct, incorrect, partially_correct)
 
     def student_view(self, context):
+        # Migrate stored data if necessary
+        self.migrate_fields()
+
         fragment, named_children = self.get_children_fragment(
             context, view_name='mentoring_view',
             not_instance_of=self.FLOATING_BLOCKS,
@@ -172,6 +174,18 @@ class MentoringBlock(XBlockWithLightChildren, StepParentMixin):
 
         return fragment
 
+    def migrate_fields(self):
+        """
+        Migrate data stored in the fields, when a format change breaks backward-compatibility with
+        previous data formats
+        """
+        # Partial answers replaced the `completed` with `status` in `self.student_results`
+        if self.student_results and 'completed' in self.student_results[0][1]:
+            # Rename the field and use the new value format (text instead of boolean)
+            for result in self.student_results:
+                result[1]['status'] = 'correct' if result[1]['completed'] else 'incorrect'
+                del result[1]['completed']
+
     @property
     def additional_publish_event_data(self):
         return {

tests/unit/test_step.py

+import copy
 import unittest
+from mock import MagicMock, Mock
 
-from lxml import etree
+from xblock.field_data import DictFieldData
 
 from mentoring import MentoringBlock
-import mentoring
 from mentoring.step import StepMixin, StepParentMixin
 
 
@@ -78,3 +79,37 @@ class TestStepMixin(unittest.TestCase):
 
         self.assertFalse(step1.lonely_step)
         self.assertFalse(step2.lonely_step)
+
+
+class TestFieldMigration(unittest.TestCase):
+    """
+    Test mentoring fields data migration
+    """
+
+    def test_partial_completion_status_migration(self):
+        """
+        Changed `completed` to `status` in `self.student_results` to accomodate partial responses
+        """
+        # Instantiate a mentoring block with the old format
+        student_results = [
+            [ u'goal',
+                {   u'completed': True,
+                    u'score': 1,
+                    u'student_input': u'test',
+                    u'weight': 1}],
+            [ u'mcq_1_1',
+                {   u'completed': False,
+                    u'score': 0,
+                    u'submission': u'maybenot',
+                    u'weight': 1}],
+        ]
+        mentoring = MentoringBlock(MagicMock(), DictFieldData({'student_results': student_results}), Mock())
+        self.assertEqual(copy.deepcopy(student_results), mentoring.student_results)
+
+        migrated_student_results = copy.deepcopy(student_results)
+        migrated_student_results[0][1]['status'] = 'correct'
+        migrated_student_results[1][1]['status'] = 'incorrect'
+        del migrated_student_results[0][1]['completed']
+        del migrated_student_results[1][1]['completed']
+        mentoring.migrate_fields()
+        self.assertEqual(migrated_student_results, mentoring.student_results)