Merge pull request #7219 from edx/mjames/SOL-289

Addresses problem with 'up' and 'down' errors within SOL-289

common/lib/xmodule/xmodule/modulestore/search.py

@@ -1,5 +1,10 @@
+''' useful functions for finding content and its position '''
+from logging import getLogger
+
 from .exceptions import (ItemNotFoundError, NoPathToItem)
 
+LOGGER = getLogger(__name__)
+
 
 def path_to_location(modulestore, usage_key):
     '''
@@ -105,3 +110,30 @@ def path_to_location(modulestore, usage_key):
             position = "_".join(position_list)
 
         return (course_id, chapter, section, position)
+
+
+def navigation_index(position):
+    """
+    Get the navigation index from the position argument (where the position argument was recieved from a call to
+    path_to_location)
+
+    Argument:
+    position - result of position returned from call to path_to_location. This is an underscore (_) separated string of
+    vertical 1-indexed positions. If the course is built in Studio then you'll never see verticals as children of
+    verticals, and so extremely often one will only see the first vertical as an integer position. This specific action
+    is to allow navigation / breadcrumbs to locate the topmost item because this is the location actually required by
+    the LMS code
+
+    Returns:
+    1-based integer of the position of the desired item within the vertical
+    """
+    if position is None:
+        return None
+
+    try:
+        navigation_position = int(position.split('_', 1)[0])
+    except (ValueError, TypeError):
+        LOGGER.exception(u'Bad position %r passed to navigation_index, will assume first position', position)
+        navigation_position = 1
+
+    return navigation_position

common/lib/xmodule/xmodule/modulestore/tests/test_mixed_modulestore.py

@@ -38,7 +38,7 @@ from xmodule.modulestore import ModuleStoreEnum
 from xmodule.modulestore.draft_and_published import UnsupportedRevisionError, DIRECT_ONLY_CATEGORIES
 from xmodule.modulestore.exceptions import ItemNotFoundError, DuplicateCourseError, ReferentialIntegrityError, NoPathToItem
 from xmodule.modulestore.mixed import MixedModuleStore
-from xmodule.modulestore.search import path_to_location
+from xmodule.modulestore.search import path_to_location, navigation_index
 from xmodule.modulestore.tests.factories import check_mongo_calls, check_exact_number_of_calls, \
     mongo_uses_error_check
 from xmodule.modulestore.tests.utils import create_modulestore_instance, LocationMixin
@@ -1153,6 +1153,18 @@ class TestMixedModuleStore(CourseComparisonTest):
             with self.assertRaises(ItemNotFoundError):
                 path_to_location(self.store, location)
 
+    def test_navigation_index(self):
+        """
+        Make sure that navigation_index correctly parses the various position values that we might get from calls to
+        path_to_location
+        """
+        self.assertEqual(1, navigation_index("1"))
+        self.assertEqual(10, navigation_index("10"))
+        self.assertEqual(None, navigation_index(None))
+        self.assertEqual(1, navigation_index("1_2"))
+        self.assertEqual(5, navigation_index("5_2"))
+        self.assertEqual(7, navigation_index("7_3_5_6_"))
+
     @ddt.data('draft', 'split')
     def test_revert_to_published_root_draft(self, default_ms):
         """