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Fix the order randomization behaviour of Randomized Content Block

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The Randomized Content Block XBlock only randomizes the selection of
the children blocks and has unpredictable randomization of
the order of the selected child blocks due to the usage of sets, which
are unordered, for storing the selected blocks. This becomes apparent
when all the available child blocks in a library are chosen for a
Randomized Content Block, to randomize just the order of the child
blocks and not just the selection of the blocks. The order of the
selected blocks ends up being similar for multiple learners.

This change modifies the XBlock to store the selected child blocks in
a list, instead of a set, after randomly shuffling them.
This commit is contained in:
Guruprasad Lakshmi Narayanan
2018-07-23 13:37:04 +05:30
parent 9189daeb58
commit 5a2b607ea6
6 changed files with 160 additions and 38 deletions
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43
common/lib/xmodule/xmodule/library_content_module.py
View File

@@ -158,37 +158,40 @@ class LibraryContentModule(LibraryContentFields, XModule, StudioEditableModule):
"""
rand = random.Random()
selected = set(tuple(k) for k in selected) # set of (block_type, block_id) tuples assigned to this student
selected_keys = set(tuple(k) for k in selected) # set of (block_type, block_id) tuples assigned to this student
# Determine which of our children we will show:
valid_block_keys = set([(c.block_type, c.block_id) for c in children])
# Remove any selected blocks that are no longer valid:
invalid_block_keys = (selected - valid_block_keys)
invalid_block_keys = (selected_keys - valid_block_keys)
if invalid_block_keys:
selected -= invalid_block_keys
selected_keys -= invalid_block_keys
# If max_count has been decreased, we may have to drop some previously selected blocks:
overlimit_block_keys = set()
if len(selected) > max_count:
num_to_remove = len(selected) - max_count
overlimit_block_keys = set(rand.sample(selected, num_to_remove))
selected -= overlimit_block_keys
if len(selected_keys) > max_count:
num_to_remove = len(selected_keys) - max_count
overlimit_block_keys = set(rand.sample(selected_keys, num_to_remove))
selected_keys -= overlimit_block_keys
# Do we have enough blocks now?
num_to_add = max_count - len(selected)
num_to_add = max_count - len(selected_keys)
added_block_keys = None
if num_to_add > 0:
# We need to select [more] blocks to display to this user:
pool = valid_block_keys - selected
pool = valid_block_keys - selected_keys
if mode == "random":
num_to_add = min(len(pool), num_to_add)
added_block_keys = set(rand.sample(pool, num_to_add))
# We now have the correct n random children to show for this user.
else:
raise NotImplementedError("Unsupported mode.")
selected |= added_block_keys
selected_keys |= added_block_keys
if any([invalid_block_keys, overlimit_block_keys, added_block_keys]):
selected = selected_keys
return {
'selected': selected,
@@ -268,19 +271,15 @@ class LibraryContentModule(LibraryContentFields, XModule, StudioEditableModule):
def selected_children(self):
"""
Returns a set() of block_ids indicating which of the possible children
Returns a list() of block_ids indicating which of the possible children
have been selected to display to the current user.
This reads and updates the "selected" field, which has user_state scope.
Note: self.selected and the return value contain block_ids. To get
Note: the return value (self.selected) contains block_ids. To get
actual BlockUsageLocators, it is necessary to use self.children,
because the block_ids alone do not specify the block type.
"""
if hasattr(self, "_selected_set"):
# Already done:
return self._selected_set # pylint: disable=access-member-before-definition
block_keys = self.make_selection(self.selected, self.children, self.max_count, "random") # pylint: disable=no-member
# Publish events for analytics purposes:
@@ -292,13 +291,13 @@ class LibraryContentModule(LibraryContentFields, XModule, StudioEditableModule):
self._publish_event,
)
# Save our selections to the user state, to ensure consistency:
selected = block_keys['selected']
self.selected = list(selected) # TODO: this doesn't save from the LMS "Progress" page.
# Cache the results
self._selected_set = selected # pylint: disable=attribute-defined-outside-init
if any(block_keys[changed] for changed in ('invalid', 'overlimit', 'added')):
# Save our selections to the user state, to ensure consistency:
selected = list(block_keys['selected'])
random.shuffle(selected)
self.selected = selected # TODO: this doesn't save from the LMS "Progress" page.
return selected
return self.selected
def _get_selected_child_blocks(self):
"""

19
common/lib/xmodule/xmodule/tests/test_library_content.py
View File

@@ -272,9 +272,8 @@ class LibraryContentModuleTestMixin(object):
Helper method that changes the max_count of self.lc_block, refreshes
children, and asserts that the number of selected children equals the count provided.
"""
# Clear the cache (only needed because we skip saving/re-loading the block) pylint: disable=protected-access
if hasattr(self.lc_block._xmodule, '_selected_set'):
del self.lc_block._xmodule._selected_set
# Construct the XModule for the descriptor, if not present already.
self.lc_block._xmodule # pylint: disable=pointless-statement,protected-access
self.lc_block.max_count = count
selected = self.lc_block.get_child_descriptors()
self.assertEqual(len(selected), count)
@@ -287,7 +286,7 @@ class TestLibraryContentModuleNoSearchIndex(LibraryContentModuleTestMixin, Libra
Tests for library container when no search index is available.
Tests fallback low-level CAPA problem introspection
"""
pass
pass # pylint: disable=unnecessary-pass
search_index_mock = Mock(spec=SearchEngine) # pylint: disable=invalid-name
@@ -365,8 +364,8 @@ class TestLibraryContentAnalytics(LibraryContentTest):
Check that a LibraryContentModule analytics event was published by self.lc_block.
"""
self.assertTrue(self.publisher.called)
self.assertTrue(len(self.publisher.call_args[0]), 3)
_, event_name, event_data = self.publisher.call_args[0]
self.assertTrue(len(self.publisher.call_args[0]), 3) # pylint: disable=unsubscriptable-object
_, event_name, event_data = self.publisher.call_args[0] # pylint: disable=unsubscriptable-object
self.assertEqual(event_name, "edx.librarycontentblock.content.{}".format(event_type))
self.assertEqual(event_data["location"], six.text_type(self.lc_block.location))
return event_data
@@ -397,8 +396,6 @@ class TestLibraryContentAnalytics(LibraryContentTest):
# Now increase max_count so that one more child will be added:
self.lc_block.max_count = 2
# Clear the cache (only needed because we skip saving/re-loading the block) pylint: disable=protected-access
del self.lc_block._xmodule._selected_set
children = self.lc_block.get_child_descriptors()
self.assertEqual(len(children), 2)
child, new_child = children if children[0].location == child.location else reversed(children)
@@ -478,8 +475,6 @@ class TestLibraryContentAnalytics(LibraryContentTest):
self.lc_block.get_child_descriptors() # This line is needed in the test environment or the change has no effect
self.publisher.reset_mock() # Clear the "assigned" event that was just published.
self.lc_block.max_count = 0
# Clear the cache (only needed because we skip saving/re-loading the block) pylint: disable=protected-access
del self.lc_block._xmodule._selected_set
# Check that the event says that one block was removed, leaving no blocks left:
children = self.lc_block.get_child_descriptors()
@@ -497,8 +492,6 @@ class TestLibraryContentAnalytics(LibraryContentTest):
# Start by assigning two blocks to the student:
self.lc_block.get_child_descriptors() # This line is needed in the test environment or the change has no effect
self.lc_block.max_count = 2
# Clear the cache (only needed because we skip saving/re-loading the block) pylint: disable=protected-access
del self.lc_block._xmodule._selected_set
initial_blocks_assigned = self.lc_block.get_child_descriptors()
self.assertEqual(len(initial_blocks_assigned), 2)
self.publisher.reset_mock() # Clear the "assigned" event that was just published.
@@ -512,8 +505,6 @@ class TestLibraryContentAnalytics(LibraryContentTest):
self.library.children = [keep_block_lib_usage_key]
self.store.update_item(self.library, self.user_id)
self.lc_block.refresh_children()
# Clear the cache (only needed because we skip saving/re-loading the block) pylint: disable=protected-access
del self.lc_block._xmodule._selected_set
# Check that the event says that one block was removed, leaving one block left:
children = self.lc_block.get_child_descriptors()