Clear cached children when binding an XModuleDescriptor/XBlock to a particular user

common/lib/xmodule/xmodule/tests/__init__.py

@@ -110,7 +110,7 @@ def get_test_system(course_id=SlashSeparatedCourseKey('org', 'course', 'run')):
         # So, bind to the same one as the current descriptor.
         module_system.descriptor_runtime = descriptor._runtime  # pylint: disable=protected-access
 
-        descriptor.bind_for_student(module_system, descriptor._field_data)
+        descriptor.bind_for_student(module_system, descriptor._field_data, user.id)
 
         return descriptor
 

common/lib/xmodule/xmodule/tests/test_library_content.py

@@ -58,7 +58,7 @@ class LibraryContentTest(MixedSplitTestCase):
             sub_module_system = get_test_system(course_id=self.course.location.course_key)
             sub_module_system.get_module = get_module
             sub_module_system.descriptor_runtime = descriptor._runtime  # pylint: disable=protected-access
-            descriptor.bind_for_student(sub_module_system, descriptor._field_data)  # pylint: disable=protected-access
+            descriptor.bind_for_student(sub_module_system, descriptor._field_data, self.user_id)  # pylint: disable=protected-access
             return descriptor
 
         module_system.get_module = get_module

common/lib/xmodule/xmodule/tests/test_split_test_module.py

@@ -81,6 +81,7 @@ class SplitTestModuleTest(XModuleXmlImportTest, PartitionTestCase):
         self.module_system.descriptor_runtime = self.course._runtime  # pylint: disable=protected-access
         self.course.runtime.export_fs = MemoryFS()
 
+        user = Mock(username='ma', email='ma@edx.org', is_staff=False, is_active=True)
         self.partitions_service = StaticPartitionService(
             [
                 self.user_partition,
@@ -90,14 +91,18 @@ class SplitTestModuleTest(XModuleXmlImportTest, PartitionTestCase):
                     MockUserPartitionScheme()
                 )
             ],
-            user=Mock(username='ma', email='ma@edx.org', is_staff=False, is_active=True),
+            user=user,
             course_id=self.course.id,
             track_function=Mock(name='track_function'),
         )
         self.module_system._services['partitions'] = self.partitions_service  # pylint: disable=protected-access
 
         self.split_test_module = self.course_sequence.get_children()[0]
-        self.split_test_module.bind_for_student(self.module_system, self.split_test_module._field_data)  # pylint: disable=protected-access
+        self.split_test_module.bind_for_student(
+            self.module_system,
+            self.split_test_module._field_data,  # pylint: disable=protected-access
+            user.id
+        )
 
 
 @ddt.ddt

common/lib/xmodule/xmodule/x_module.py

@@ -17,8 +17,11 @@ from webob import Response
 from webob.multidict import MultiDict
 
 from xblock.core import XBlock, XBlockAside
-from xblock.fields import Scope, Integer, Float, List, XBlockMixin, String, Dict, ScopeIds, Reference, \
-    ReferenceList, ReferenceValueDict
+from xblock.fields import (
+    Scope, Integer, Float, List, XBlockMixin,
+    String, Dict, ScopeIds, Reference, ReferenceList,
+    ReferenceValueDict, UserScope
+)
 from xblock.fragment import Fragment
 from xblock.runtime import Runtime, IdReader, IdGenerator
 from xmodule.fields import RelativeTime
@@ -281,6 +284,8 @@ class XModuleMixin(XBlockMixin):
 
     def __init__(self, *args, **kwargs):
         self.xmodule_runtime = None
+        self._child_instances = None
+
         super(XModuleMixin, self).__init__(*args, **kwargs)
 
     @property
@@ -410,7 +415,7 @@ class XModuleMixin(XBlockMixin):
         if not self.has_children:
             return []
 
-        if getattr(self, '_child_instances', None) is None:
+        if self._child_instances is None:
             self._child_instances = []  # pylint: disable=attribute-defined-outside-init
             for child_loc in self.children:
                 # Skip if it doesn't satisfy the filter function
@@ -525,15 +530,39 @@ class XModuleMixin(XBlockMixin):
         """
         return None
 
-    def bind_for_student(self, xmodule_runtime, field_data):
+    def bind_for_student(self, xmodule_runtime, field_data, user_id):
         """
         Set up this XBlock to act as an XModule instead of an XModuleDescriptor.
 
         Arguments:
             xmodule_runtime (:class:`ModuleSystem'): the runtime to use when accessing student facing methods
             field_data (:class:`FieldData`): The :class:`FieldData` to use for all subsequent data access
+            user_id: The user_id to set in scope_ids
         """
         # pylint: disable=attribute-defined-outside-init
+
+        # Skip rebinding if we're already bound a user, and it's this user.
+        if self.scope_ids.user_id is not None and user_id == self.scope_ids.user_id:
+            return
+
+        # If we are switching users mid-request, save the data from the old user.
+        self.save()
+
+        # Update scope_ids to point to the new user.
+        self.scope_ids = self.scope_ids._replace(user_id=user_id)
+
+        # Clear out any cached instantiated children.
+        self._child_instances = None
+
+        # Clear out any cached field data scoped to the old user.
+        for field in self.fields.values():
+            if field.scope in (Scope.parent, Scope.children):
+                continue
+
+            if field.scope.user == UserScope.ONE:
+                field._del_cached_value(self)
+
+        # Set the new xmodule_runtime and field_data (which are user-specific)
         self.xmodule_runtime = xmodule_runtime
         self._field_data = field_data