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feat: add endpoint to delete or archive a CompetencyCriterion (#674) - #879
Adds a DELETE endpoint that removes a CompetencyCriterion (the association between a gradeable object and a competency in a criteria tree). When no learner mastery status references the criterion, the row is hard-deleted; when one does, the row is archived in place (archived=True), so learner progress already recorded against it stays intact and auditable. The response is 200 {"id": ..., "archived": false|true} in both cases, and a repeat DELETE on an archived row returns the same body again.
Untagging. On a hard delete, the criterion's own ObjectTag row is deleted directly through the ORM, and only when no other CompetencyCriterion still references it (the same tagged object can be used in two different groups). No other ObjectTag on the object is touched. The archive path never touches the ObjectTag.
Group cascade. Removing a criterion can leave its leaf CompetencyCriteriaGroup, and ancestors above it, with no children. The delete walks the ancestor chain and hard-deletes each emptied group, or archives it when a StudentCompetencyCriteriaGroupStatus row references it, so no empty group persists (ADR-0002 Decision 2). The delete-vs-archive choice, for the criterion and for each cascaded group, is a server-side decision driven entirely by learner-status presence.
Concurrency. Every writer of a competency's criteria now follows one rule: take that competency's Tag row lock first, read mutable state only after it, take no other group or criterion row lock, and save criteria in ascending primary-key order. The delete takes that lock around the re-read, the learner-status check, and the cascade. This PR also moves the two existing writers that predate it onto the same rule, because the old shapes could deadlock against the delete (the delete held the criterion row and waited for the leaf group, while a bulk update held the group rows and waited for the criterion, an unhandled OperationalError 1213 on MySQL):
bulk_update_competency_criteria drops its two select_for_update() calls (group lineage and criteria) in favor of the Tag lock, runs its archived and membership checks after the lock, and saves in primary-key order, the same order in which the grading write locks criterion rows.
update_competency_criteria_group takes the Tag lock and re-reads the group under it, so racing a delete now yields a clean 404 or archived-conflict error instead of a DatabaseError or a silent write onto an archived group.
A grade write that races a hard delete fails one side with an IntegrityError, never silently: if the status insert commits first, the delete fails its foreign-key check and a second click archives the criterion; if the delete commits first, the grade's insert fails inside the learner's transaction. The delete docstring records this, the three races the Tag lock prevents, and the READ COMMITTED assumption.
Tests. A new MySQL-only test file, test_criterion_concurrency.py, exercises the locks over two database connections: the Tag lock held across the request, a create waiting and surviving, two sibling deletes leaving no empty leaf, delete racing bulk update (the old deadlock, now a clean error), delete racing the group PATCH, and grade-write-vs-delete in both orderings. The file skips on SQLite, where select_for_update is a no-op, and runs in CI's MySQL job. Lock-point tests that run on SQLite pin each writer's lock: that the delete, bulk update and group update read current state only after taking it, and that create_competency_criterion takes it at all. The pk-ordered save loop is pinned by a SQLite call-order test; no MySQL test observes the lock order itself.
This change affects the Course Author / Platform Administrator roles (correcting or retiring a mastery rule). It is a backend API addition; the Studio UI that calls it (#710) is separate.
Amends ADR-0002 (Decision 7: the roll-up tables are never relied on alone to protect a record) and ADR-0004 (Decision 6: the no-lock rule covers learner-status writers only), each with a dated changelog entry.
The mastery rollup still counts archived children when combining a group's children, so an AND group with an archived leaf cannot be demonstrated by a learner who starts after the archive. Grade recording already skips archived criteria on main; [BE] Exclude archived criteria and groups when rolling up a learner's competency status #815 owns excluding archived rows from the rollup. This PR is the first code that archives these rows.
ADR-0002 Decision 7's wording now says the roll-up tables are never relied on alone to protect a record, since the delete cascade checks StudentCompetencyCriteriaGroupStatus directly before a group hard-delete. ADR-0004 Decision 6's no-lock rule is narrowed to learner-status writers, since the authoring writers serialize on the Tag row. Both amendments carry changelog entries; the empty-group enforcement and the archived criterion's live ObjectTag stay within the existing ADR text (the ObjectTag is ultimately handled by [BE] Stop an assignment showing as tagged when the last competency rule measuring it is archived #817).
No new model fields or migrations. Not in scope here (left to #675, the group-level counterpart): deleting or archiving a CompetencyCriteriaGroup directly, and the Studio in-use warning/confirmation flow ADR-0003 Decision 4 requires before calling this endpoint.
Added an authenticated endpoint to remove competency criteria. Criteria without learner progress are deleted; criteria with progress are archived instead.
Empty groups may also be removed or archived as part of criterion removal.
Criterion responses now include whether a criterion is archived.
Bug Fixes
Missing competency tags now return 404 in affected update requests. Conflicts during deletion return a retryable 409 response.
Documentation
Clarified how learner-status records and locking affect criterion protection and concurrent updates.
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Thanks for covering the fallback path with tests. I'm having trouble working out which real concurrency situations these tests stand for. Could you add a short explanation, either in the PR description or in the docstrings of delete_competency_criterion and these tests? It would help to cover:
Which races can actually happen here. For example: a grade write adds a status row on the criterion, or on an ancestor group, between the status check and the delete. For each race, which concurrent operation causes it?
Which of those races the criterion row lock at api.py:520 already prevents. If the lock blocks a concurrent status insert on the criterion, can test_status_on_the_criterion_missed_by_the_first_check_archives_it still happen in practice, or is that path only defensive?
How each test maps to one of those races. The tests force a stale check with side_effect=[False, True], so it's hard to tell from the tests alone which real interleaving each one stands for.
A sentence or two per race would be plenty. Thanks!
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The docstring of delete_or_archive_competency_criterion now lists them. There are two: a concurrent create for the same competency, which now waits on the Tag row lock, and a learner-status insert on the criterion or on one of its ancestor groups, which waits on that row's lock. Both are prevented by the locks, so the side-effect tests that simulated a stale check are removed.
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It was the ancestor-group status check inside _cascade_from_group on the first of two attempts. The retry is gone, so there is only one check, made while the ancestor groups are locked. The test is removed.
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The retry existed to recover from an ancestor gaining a status between the cascade's check and its delete. Locking the ancestor groups closes that window, so the retry is removed, and any integrity error now propagates on the first attempt.
Here's a pretty in-depth AI review. The points it makes sound right to me.
Review of PR #879: delete or archive a CompetencyCriterion
Review Details
Prerequisites, deferred items, what passed, and the action list
Prerequisites (skip if you know the codebase)
The models. A CompetencyCriteriaGroup is a node in a per-competency tree: a root group per tag, a course-level group per course under the root, and leaf groups under that. Its parent foreign key points upward (child_groups is the reverse name). A CompetencyCriterion hangs off a leaf group (group, reverse name criteria) and points at an ObjectTag (object_tag), the tagging-system row that says "this subsection carries this competency tag". Both the group and the criterion have an archived boolean (added by #716). Two learner-status models exist: StudentCompetencyCriterionStatus references a criterion, and StudentCompetencyCriteriaGroupStatus references a group. Both use on_delete=PROTECT, so the database refuses to delete a row they point at. By contrast CompetencyCriteriaGroup.parent, CompetencyCriterion.group, and CompetencyCriterion.object_tag are all CASCADE, which Django emulates in Python by re-querying the children at delete time. Ticket #674 calls the criterion-status model StudentCompetencyCriteriaStatus; the class on main is StudentCompetencyCriterionStatus.
What the change adds.delete_competency_criterion(criterion_id) in the applet's api.py opens a transaction, locks the criterion row with select_for_update(), and either archives it (if a status row references it) or deletes it. On the delete branch it also removes the ObjectTag through the tagging API's tag_object() read-merge-write, but only when no other criterion still references that ObjectTag. It then walks up the group tree (_cascade_from_group), deleting or archiving each ancestor left with no live child. If the database refuses the delete (ProtectedError or IntegrityError), the function re-checks the criterion's status, archives it if one exists, and otherwise retries the whole attempt once. A new CompetencyCriterionDeleteView at DELETE /api/cbe/v1/competencies/<tag_id>/criteria/<criterion_id>/ resolves the row, checks oel_tagging.can_tag_object inline, calls the function, and returns 200 {"id", "archived"}. The shared CompetencyCriterionSerializer gains a read-only archived field.
Names the tickets coined. "Cascade" or "the walk" is the ancestor loop just described. An "archive event" versus a "delete event" is the mode the walk runs in: after an archive it only archives; after a delete it deletes a group that is fully empty and archives one whose only remaining children are archived. "Delete protection" is ADR-0002 Decision 7: a row referenced by learner status is archived instead of deleted.
The ADRs cited (in docs/openedx_learning/decisions/): ADR-0002 (competency criteria model, including Decision 2, the rule that no empty group persists, and Decision 7, delete protection), ADR-0003 (competency criteria versioning), ADR-0004 (competency mastery concurrency, which covers the grade write).
Database terms (unsourced, general knowledge). select_for_update() takes a row lock until the transaction ends. ATOMIC_REQUESTS is the Django setting that wraps each request in one transaction. READ COMMITTED and REPEATABLE READ are transaction isolation levels: the first lets a query see rows other transactions committed meanwhile, the second reads a fixed snapshot. django-simple-history writes a history row on every save(), and _history_user names the user on that row.
The tickets around this one.#674 is this ticket. #665 built the create endpoint and the associate_competency_criterion function this PR mirrors. #716 added the archived fields. #675 (open) will delete or archive a whole group directly and expects to reuse this PR's cascade helper. #709 and #710 (open, frontend) will call this endpoint; #710 names the URL shape DELETE .../competencies/<tag_id>/criteria/<criterion_id>/ and expects a removed subsection to be "selectable again" afterwards. #874 landed on main after this branch was cut: it adds a bulk-update endpoint that takes user, checks permission inside the API function, locks groups before criteria, and refuses with a 409 any edit to criteria under an archived group or archived ancestor.
How the endpoint reaches Studio. edx-platform's cms/urls.py includes openedx_learning.urls under api/, which includes this applet's rest_api/v1/urls.py under cbe/. The permission rule lives in edx-platform's content_tagging/rules.py and derives the course from whatever key string it is given, so a usage key works.
How the review tested the tests. For each acceptance criterion the review broke the code path on purpose (for example, forced the status check to return False, or made the cascade return immediately), ran the two new test files, and checked that at least one test failed for that reason. A break that left all 68 tests green means the behavior is untested.
Things the review looked at and is leaving to other tickets
Deleting or archiving a CompetencyCriteriaGroup directly: [BE] Build endpoint for removing a Competency Criteria Group #675 owns it, and it can call _cascade_from_group(target.parent, event) as written; it will inherit whatever lock and save changes this PR makes.
At the head commit, the two touched test files pass (68 tests), pylint on the six touched files is clean, mypy on the four source files is clean, lint-imports keeps all three contracts, and makemigrations --check reports no changes, both at head and on the merged tree. Every acceptance criterion except the two test gaps below has a test that fails when its behavior is broken. The permission object is built from stored data rather than from the URL so a caller cannot reach another course's criterion through a tag they can view, the route is mounted in Studio through the existing include, and the URL shape matches what #710 will call. The review could not run anything that depends on row locks, because the test database is SQLite.
Decide and record how archived groups come back, and whether the duplicate check should ignore archived criteria now; state the limitation in the PR description.
Move the permission check into delete_competency_criterion with a user argument and set _history_user, or record the deviation from [BE] Delete Competency Criterion #674.
Lock the Tag row before the criterion, as the create path does; consider locking ancestor groups and dropping the retry.
Untag only when the criterion's ObjectTag is among the rows get_object_tags() returned.
Map CompetencyCriterion.DoesNotExist to NotFound in the view.
Make the test changes described in the test findings and in the depth-2 improvement.
Fix the two docstrings, and update the PR description (deviations section, cherry-pick paragraph, model name, how to create a status row).
Record the two ADR tensions (group-status check, live ObjectTag on archive), settle the grading-write and PostgreSQL questions, and decide the remaining items under "Decisions to make or write down".
Do the remaining improvements and small things.
Must fix before merge
The branch no longer merges cleanly with main, and once merged it makes an existing test fail.
Details
The branch conflicts with main and breaks a bulk-update test. Merging the head onto current main conflicts in the applet's api.py import block, urls.py, views.py (three places), and test_views.py (two places), all additive side-by-side insertions from this PR and from #874. After resolving them by keeping both sides, test_bulk_update_with_rule_values_echoes_every_criterion_as_stored fails: it compares the response keys to a fixed set, and the shared serializer now also emits archived. Rebase onto main, add archived to that test's expected key set, and say in the PR description that the bulk-update response now carries archived too. The migration check and the import linter pass on the merged tree.
Once this change archives a group, nothing in the system can bring it back, and other features get stuck on it.
Details
Nothing can ever un-archive a group, and the create path and bulk update both get stuck on archived groups. This PR is the first code that archives groups. Once the walk archives a course-level group (or the root group that every course shares for that tag), three existing pieces of code turn that into a dead end. The create path's _create_leaf_group reuses archived root and course-level groups through get_or_create, by design, and the unique constraint on (tag, course, parent) has no condition, so no live replacement course-level group can exist. The duplicate check _reject_duplicate_criterion counts archived criteria, so re-associating the same subsection with the same competency without a group_id is rejected as a duplicate, which contradicts #710's "selectable again" criterion. And #874's bulk_update_competency_criteria on main refuses with a 409 any edit under an archived group or ancestor. Put together: an author removes a criterion that has learner progress, then adds a different subsection to the same competency in the same course; the new criterion lands under the archived course-level group and can never be edited through the bulk-update endpoint. #675's open questions mention this reactivation problem and defer it to a follow-up ticket that does not exist. Before #709/#710 ship, decide and write down (an amendment to ADR-0002 Decision 2 or a follow-up ticket) that a container archived only because it emptied is reactivated when the create path adds a live child under it, and that the duplicate check ignores archived criteria. State the limitation in the PR description now.
The permission check happens only in the web endpoint and not in the delete function, which departs from the ticket and from how newer code on main does it.
Details
The permission check lives only in the view, and the function takes no user. Ticket #674 asked for delete_competency_criterion(criterion_id, user) with the can_tag_object check inside the function. The PR puts the check in CompetencyCriterionDeleteView.delete and the function takes only criterion_id. That matched associate_competency_criterion at the time, but #874 on main now takes user, checks permission inside bulk_update_competency_criteria, and sets _history_user on the rows it saves so the audit rows name who did it. After the rebase, the module's only destructive exported function would follow the older convention: any in-process caller can delete criteria unchecked, and the archive's history rows carry no user outside the CMS middleware. Take user, check inside the function, set _history_user on the rows the archive saves, and record the deviation from #674 either way. Also settle which key the permission object carries: the create view passes the subsection's usage key, #874 passes the course key; edx-platform's rule accepts both.
The delete does not take the same lock the create takes, so on some databases a create happening at the same moment can be silently deleted.
Details
The delete path skips the Tag-row lock the create path relies on, so a concurrent create can be silently deleted.associate_competency_criterion holds Tag.objects.select_for_update() across its duplicate check, its group get_or_create, and its tag_object() call. The delete path locks only the criterion row. Deleting a group or an ObjectTag cascades to whatever children exist at that moment. The failure depends on the database's isolation level, and the review could not run it (the test database is SQLite, which ignores row locks). On PostgreSQL, or MySQL under READ COMMITTED, a leaf group or criterion that another request committed between the walk's emptiness check and group.delete() is collected and deleted while that other request already returned 201. On MySQL's default REPEATABLE READ (edx-platform sets no isolation level) the collector's snapshot misses the new row, the database foreign key refuses the delete, and the retry runs and stops correctly, so the loss becomes a retry. A second association that reuses the ObjectTag being untagged is exposed the same way. Read the criterion's group.tag_id without a lock, lock the Tag row, then lock the criterion, matching the create path.
Untagging works out which tags to keep from a query that hides disabled-taxonomy tags but deletes through one that does not, so with the competency taxonomy disabled it can delete other competencies' tags on the same subsection, or fail with a protected-row error; only callers that bypass the web endpoint reach this.
Details
Untagging reads through a filtered query but writes through an unfiltered one. The delete branch builds the list of tag values to keep from get_object_tags(), which hides tags of disabled taxonomies and deleted tags, and hands it to tag_object(), which deletes every ObjectTag it finds that is not in the list, with no such filter. With the competency taxonomy disabled, the keep list is empty and every ObjectTag of that taxonomy on the object is deleted, cascading to the other competencies' criteria on that subsection; if one of those has a learner status the call raises ProtectedError instead. The review reproduced both outcomes by calling the function directly. The REST path is refused earlier (the permission rule requires an enabled taxonomy), so only in-process callers reach this. Untag only when the criterion's object_tag.id is among the rows get_object_tags() returned, and raise otherwise.
Sending the same delete request twice at nearly the same time can produce a server error instead of a not-found response.
Details
A concurrent repeat DELETE returns 500 instead of 404. The view resolves the criterion with get_object_or_404, then the function re-reads it with select_for_update() and raises CompetencyCriterion.DoesNotExist if it has gone. The view maps only Http404 and PermissionDenied; the create view maps DoesNotExist to NotFound. A double click on the remove control in #710 sends two requests; the second waits on the row lock and then raises. Catch CompetencyCriterion.DoesNotExist around the API call and raise NotFound.
Two tests meant to check where the ancestor cleanup stops do not fail when that rule breaks.
Details
The cascade's stop rule is tested only as "the row still exists". The two tests for "the walk stops at an ancestor with a surviving sibling" (test_single_child_leaf_group_cascade_deletes_while_a_sibling_keeps_the_root_alive and test_cascade_stops_at_an_ancestor_with_a_surviving_sibling_group) assert that the root still exists but not that it is still live. When the review forced the walk to treat every level as having no live child, the root with a live sibling was archived and all 68 tests passed. Add root.refresh_from_db() and assert root.archived is False in both, and the same for the sibling groups.
One behavior the ticket describes has no test that fails when it breaks.
Details
No test covers a hard delete whose group keeps only archived siblings. The ticket says that when a hard delete leaves a group with nothing but archived children, the group is archived and the walk continues upward as an archive. The code does this correctly (the review probed it), but when the review removed that branch, all 68 tests still passed. Add a service test with one archived criterion (with a status) and one live criterion in the same group, delete the live one, and assert the group and its parent end up archived.
The permission-denied test would still pass if the check ran too late, and one half of the permission rule has no test.
Details
The 403 test proves only the status code, and half of the permission is untested.test_delete_no_permission_is_403 denies the object-id half of the rule and asserts the 403. When the review moved the permission check to after the delete call, the test still passed, because the row was already gone by the time the 403 was raised and the test never looks. Assert afterwards that the criterion and its ObjectTag still exist. Separately, nothing exercises the taxonomy-view half of can_tag_object (the "lacks view access to the taxonomy" clause of the acceptance criterion); add a case where the taxonomy permission is denied and the object id is allowed.
The documented reason for the endpoint's URL shape is wrong, and the ticket is never told the URL differs from what it specified.
Details
The view docstring gives a false reason for the URL shape and the PR hides the change from the ticket. Ticket #674 specified criteria-groups/<group_id>/criteria/<criterion_id>/ with a group mismatch returning 404. The PR uses competencies/<tag_id>/criteria/<criterion_id>/ and the docstring says "a group-scoped delete is a separate ticket's concern (direct group deletion/archival)". #675, the group-deletion ticket, is itself tag-scoped, so that sentence is wrong. The tag-scoped shape is the better choice: #710 names exactly this URL and carries no group id. Say that in the docstring instead, list the deviation under a "Deviations from #674" heading in the PR description, and update #674.
The pull request description is out of date and uses a wrong class name.
Details
The PR description is stale. It says #613 "has not landed on main yet" and that the branch cherry-picks its migrations plus a renumbering commit. The PR has three commits, no migrations, and #613 landed on main before the branch point. It also names the criterion-status model StudentCompetencyCriteriaStatus (the class is StudentCompetencyCriterionStatus), and manual testing step 2 gives no way to create a status row. Delete the cherry-pick paragraph, fix the model name, say how to create a status (Django shell, admin, or record_graded_object_statuses), and add the deviations list (URL shape, permission placement, archived on the bulk-update response).
One docstring claims a rule that only the create endpoint enforces, not the data model.
Details
_cascade_from_group's docstring states an invariant no constraint enforces. It says "group.criteria only has rows at the true-leaf level". Only the create endpoint's resolve_supplied_leaf_group enforces that; ADR-0002 Decision 2 allows mixed groups, and the PR's own tests create criteria directly under root groups. The argument that actually carries correctness, that checking both relations at every level is harmless, is the second sentence. Drop the leaf claim and keep that sentence.
Decisions to make or write down
The implementation checks something an architecture decision says is not checked for this purpose, and which rule wins is unrecorded.
Details
Checking group status directly departs from ADR-0002 Decision 7. The ADR calls StudentCompetencyCriteriaGroupStatus a roll-up table "not independently checked for this purpose", because the roll-up can lag behind leaf progress. #674's acceptance criterion (AC12) requires the check, and the walk does it in _group_has_status. The foreign key is PROTECT anyway, so the check only turns a would-be database error into an archive. Record which rule wins, in one line on the PR, and ask a human to clarify the ADR.
After an archive the competency tag stays visible on the subsection, which differs from what an architecture decision describes.
Details
Leaving the ObjectTag live on the archive path is not what ADR-0003 Decision 3 describes. The ADR says that after a status exists, disassociation is archive-only and ordinary reads exclude archived rows; ObjectTag has no archived column, so the subsection keeps showing the competency tag in the tagging UI. #674 accepts this for the MVP. Record it as an ADR-0003 amendment or a follow-up ticket.
A hard delete that lands at the wrong moment can make a learner's grade save fail.
Details
A hard delete can now fail a learner's grade write.record_graded_object_statuses reads the live criteria for a graded object, then inserts status rows. A criterion that no learner has a status on yet, hard-deleted between that read and that insert, makes the insert fail its foreign key inside the grade's transaction. The window is small, but the failure lands in grading. Ask the owner of ADR-0004 whether the leaf-status write should skip a criterion that has disappeared.
Answering not-found before checking permission lets an unauthorized caller learn which criterion ids exist.
Details
404 before 403 lets an unauthorized caller enumerate criterion ids under a tag. The view looks the row up before checking permission, so a caller without rights learns which (tag, criterion) pairs exist by walking sequential ids. The create view discloses only whether a tag exists. Decide whether to check permission against the tag's taxonomy before the lookup.
One test covers a situation that no supported input can produce.
Details
One test pins a path no supported input reaches.test_unrelated_integrity_error_propagates_without_archiving injects an IntegrityError from tag_object and asserts the call count is 2. Keep it only if "retry exactly once" is a deliberate contract, and say in its docstring that the error is injected because no supported input produces it.
Improvements worth doing
The cleanup loop rewrites rows that did not change and saves more columns than it needs to.
Details
The walk re-saves levels that do not change, and uses full saves. A repeat DELETE on an archived criterion re-saves the criterion and every ancestor, writing one history row per level with nothing changed in it. CompetencyCriterion.save() re-runs full_clean(), so an archive can be refused by an override payload that was valid when it was written. A full save() also overwrites columns another request edited meanwhile. Stop the walk at a level that is already archived, and use save(update_fields=["archived"]) as #874 does.
The delete leans on a retry where locking the rows up front would be more reliable and would avoid a possible deadlock.
Details
Lock the rows the checks read instead of retrying. The retry cannot loop or archive twice, and both archive call sites are inside a transaction. But locking the Tag row, then the ancestor groups, then the criterion keeps the status checks from going stale, which is the only reason the fallback block exists, and it matches #874's groups-before-criteria lock order. The current order (criterion first, then group writes) can deadlock against a concurrent bulk update, which would surface as an uncaught OperationalError and a 500. If the retry stays, except IntegrityError alone is enough: ProtectedError is a subclass of it in Django 5.2.
A result type returned by a public function is not exported.
Details
Export CriterionDeletionResult. It is returned by an exported function but is not in __all__ and has no UNSTABLE marker. The precedent, GradedObjectScore, lives in data.py and is exported.
One scenario is covered only by a mocked test and not by a real one.
Details
Add the depth-2 variant of the "group with its own status" case. The real test puts the status on the leaf group; the ancestor case is covered only by a mocked test. One extra parametrize row with the status on the root is enough; the review probed it and it works.
Two tests simulate a race by scripting call counts, so they would break for the wrong reason.
Details
Simulate the race instead of scripting helper call counts. Two tests patch a private helper with side_effect=[False, True]. If a later change adds one more status check per attempt, those tests raise StopIteration instead of failing on behavior. Use a side-effect function that inserts the real status row on its first call and then delegates to the real helper.
Small things
A commit subject line is longer than the repository guidance asks for (73 characters against "under 72"), though CI's commitlint passed.
Details
Commit 47b564a's subject is 73 characters; the repo's own guidance asks for under 72. CI's commitlint passed.
The same retry explanation is written out three times in the code.
Details
The retry rule is explained three times: in the delete_competency_criterion docstring, in the comment inside the except, and in the trailing comment. Keep the docstring paragraph and one short why-comment.
A helper's name and the main docstring's emphasis do not describe the code as well as they could.
Details
_remove_competency_criterion reads like a second public verb; _attempt_delete_competency_criterion says what it is. The public docstring spends most of its length on the retry rather than on the contract.
A lock comment suggests more protection than the lock gives.
Details
The lock comment in _remove_competency_criterion reads as if the lock settles the race; it only covers status inserts against this one criterion, which is why the retry exists.
Several tests have redundant assertions, overlapping cases, or loosely worded names and docstrings.
Details
Tests: two exists() assertions right after refresh_from_db() cannot fail; test_unknown_criterion_id_404s and test_repeat_delete_after_hard_delete_404s go through the same lookup; hard-delete versus archive could be one parametrized test per file; several docstrings restate the test name; test_repeat_call_on_an_already_archived_criterion_is_idempotent describes how rather than what; test_create_response_reports_archived_false could be one assertion in an existing create test; "leaf-agnostic" in the criterion fixture docstring is jargon.
The URL name differs slightly from the one the ticket gives.
Details
The URL name is criterion-delete; #674 says competency-criterion-delete. The shorter name matches criterion-create; note it on the ticket.
@jesperhodge Thanks, this was a thorough review, and the main points were right. I rebased onto main (which brought in #874) and reworked the delete path. Summary of what changed, by your action list:
Rebase and feat: add bulk update competency criteria endpoint #874. Rebased onto current main; the conflicts were additive. The shared serializer's archived field now also appears in the bulk-update response, so CRITERION_FIELDS in the bulk-update view test includes it. The PR description says so.
Permission inside the function. The function is now delete_or_archive_competency_criterion(criterion_id, user), following feat: add bulk update competency criteria endpoint #874: it checks oel_tagging.can_tag_object itself before taking any lock, and the archive writes set _history_user. The permission object carries the criterion's ObjectTag.object_id (the subsection's usage key), the same object the create view checks; edx-platform's rule accepts both that and a course key.
Locks instead of the retry. One transaction now locks the competency Tag row, then the criterion's ancestor groups in pk order, then the criterion, the same Tag-first order create uses and the same groups-before-criteria order as feat: add bulk update competency criteria endpoint #874. The ancestor chain is read after the Tag lock. With those locks held, a concurrent create waits on the Tag lock, and a learner-status insert on the criterion or any ancestor waits on that row's lock, so the status checks cannot go stale. The ProtectedError/IntegrityError fallback and the retry are gone; any integrity error propagates. I also added order_by("pk") to feat: add bulk update competency criteria endpoint #874's group lock in bulk_update_competency_criteria, so both writers take group locks in the same order.
Untagging. The hard-delete branch now removes the ObjectTag only if it is among the rows get_object_tags() returned, and otherwise raises a ValidationError keyed object_id before writing anything. Since the permission check now runs inside the function, a disabled taxonomy is refused there first, so this guard is defense in depth.
404 for a concurrent repeat DELETE. The view maps CompetencyCriterion.DoesNotExist to NotFound (and Django ValidationError to a 400, like the create view).
Tests. The two "stops at a surviving sibling" tests now assert the root and siblings stay archived=False. New tests cover: a hard delete next to an archived criterion (the group and its parent end up archived); learner progress on the root (depth 2, parametrized); the 403 view test also asserts the criterion and ObjectTag survive; a 403 for the taxonomy half of can_tag_object; an API-level refusal for a user without permission; the history user on the archived rows; a repeat delete writes no history rows; the disabled-taxonomy untag guard. The tests that scripted side_effect=[False, True] and the injected IntegrityError test are removed, because the paths they covered no longer exist.
Docstrings and PR description. The view docstring now says the URL is tag-scoped because [FE] Manage & Apply Competencies: delete a Competency Criteria Association #710 calls exactly this shape and carries no group id. _cascade_from_group no longer claims that only true leaves hold criteria. The PR description is rewritten (deviations, model name, how to create a status row; the stale cherry-pick paragraph is gone).
ADR questions. I posted those separately below, since they need a human decision rather than code.
Improvements and small things. Archive writes use save(update_fields=["archived"]) and stop at a level that is already archived, so a repeat DELETE writes no history. CriterionDeletionResult moved to data.py and is exported. The helpers are renamed _criterion_has_learner_progress / _group_has_learner_progress. The retry explanation that appeared three times is gone with the retry. The fixture docstring no longer says "leaf-agnostic", and the redundant exists() assertions after refresh_from_db() are removed.
Two things I kept as they are, with the reason:
404 before 403. The view still looks the row up before checking permission, as [BE] Delete Competency Criterion #674's acceptance criteria require (403 without rights, 404 for an unknown id). Criterion ids are sequential and low-value, and the tag's existence is already disclosed by the create endpoint.
full_clean() on archive.CompetencyCriterion.save() calls full_clean() itself, so update_fields=["archived"] does not skip it, and an archive can still be refused by an override payload that has since become invalid. Changing that means changing the model's save(), which I left out of this PR.
Lock behavior cannot be exercised by the test suite, because the tests run on SQLite, where select_for_update() does nothing; the lock order is checked by review only. The 73-character subject on one commit stays as is; commitlint passes it.
Hi @ufedaseyeuconsultant , select_for_update() establishes db locks. Those can have far reaching consequences in edx-platform and break things, and Dave warned us to be cautious with these. So we should try to avoid them unless they are absolutely necessary.
According to Claude, these locks are unnecessary and can be removed:
L779-781: remove the lineage lookup and the ancestor-group select_for_update().
L783: drop select_for_update(), but keep the re-read.
L790-796: drop select_for_update() on the ObjectTag and the lock comment at L790-792. Keep the still_referenced check.
And you'd need to clean up the code around that to account for removing these a bit.
The one lock we might be leaving is the tag lock with the select_for_update() on line 778 -
. The lock is already established by tag creation and prevents a real race condition. But please add a comment to @ormsbee about this select_for_update() double checking with him that it is fine.
A criterion is archived because a learner has a status on it.
That learner's user row is deleted. Status rows CASCADE on user deletion (learner_status.py:126-128).
A repeat DELETE now takes the hard-delete branch, deletes the criterion, and the walk stops at the archived leaf group.
I wrote a probe test for this. Afterwards, the leaf and root groups both remain in the database: archived, with no group status, and the leaf with no criteria or child groups at all. That breaks #674's "no empty group is ever left persisted" (ADR-0002 Decision 2). The reviewed commit had no early return and would have deleted both groups.
The early return came from the review's own suggestion to stop at archived levels. The fix is to short-circuit an archived group only on an archive event, where nothing changes anyway. On a delete event, an archived group that is now completely empty and has no group status should still be deleted, and the walk should continue upward. Otherwise it should stop without saving. A test for this case would pin it down. Reachability is low, but it is a correctness gap.
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Hi Seva, thanks for the good fixes.
I found two more things - see the two comments I left in the PR next to this.
Most importantly we should make sure we don't use select_for_update() where it's not strictly necessary.
The lineage lookup and the ancestor-group select_for_update() are gone, along with the _lineage_group_ids() helper that only they used.
The criterion is still re-read inside the transaction, after the Tag lock, without select_for_update(). A criterion deleted by a concurrent call is still reported as DoesNotExist, which the view maps to 404.
The ObjectTag is no longer locked. After the criterion is deleted, its ObjectTag is deleted only when no other criterion references it.
I also reverted the .order_by("pk") this PR had added to the group lock in bulk_update_competency_criteria. It only existed to keep a common lock order with the ancestor locks, so with those gone it is no longer needed, and that code now matches main.
The only lock left is the Tag select_for_update(). A create for the same competency takes that lock first, so a concurrent create waits until the delete commits. The docstring now says this.
Without the group and criterion locks, a learner status written at the same moment as a hard delete is not waited for. In that case, the database foreign key from the status row to the criterion makes one of the two writes fail with an integrity error, so the outcome is an error response rather than silent data loss.
Reply to the archived-group cascade comment
Fixed. _cascade_from_group now treats an archived group differently depending on the event:
On an archive event, it stops at an archived group, as before.
On a delete event, it deletes an archived group that the delete left with no criteria, no child groups and no group-level status, and then continues the walk upward. In every other case it stops there without saving, so no redundant history row is written.
New tests in test_criterion_removal.py:
test_delete_after_the_learner_is_gone_deletes_the_emptied_archived_groups covers your scenario. A criterion is archived because a learner has a status on it, then the learner is deleted, then the criterion is deleted again. The criterion, its leaf group and its root group are all gone afterward. This test fails on the previous code.
test_delete_leaves_an_archived_group_that_still_holds_an_archived_criterion: the archived leaf keeps another archived criterion, so the leaf and its parent stay archived, with no new history row.
test_delete_leaves_an_emptied_archived_group_that_has_its_own_status: an archived leaf emptied by the delete stays, because a learner group-level status still references it.
Concurrency verdict. The Tag-lock design is sound for MVP. The three races the delete docstring names are real, and the lock closes each one. The writers that never take the lock (the grade write, the rollup, tagging-layer deletes, and the Tag, Taxonomy and CourseRun cascades Jesper covered) can only fail loudly, never lose data silently. Moving bulk update and the group PATCH onto the same lock belongs in this PR, since the new delete is what created the opposite lock order with the old bulk update.
Fix before merge
test_views.py:2024-2230: no unauthenticated DELETE test. The bulk update, tree and group update endpoints each have a 401 test (:1103, :1328, :1990), and this view declares its own IsAuthenticated gate, so dropping it would pass every current test.
test_views.py:2119 and :2139 hand-build the unauthorized usage key. The file's usage_key(course_run, UNAUTHORIZED_MARKER) helper (:663) and the parametrized form at :1939 are the established pattern. One parametrized test covers both.
Decision to write down
api.py:444: create_competency_criterion() now takes the Tag lock itself, on top of the one its only caller associate_competency_criterion() already holds (api.py:594). I read this as defense for a future direct caller, since the delete now depends on every creator holding the lock. Is that the reason? If so, one sentence saying so is enough; if not, drop the call and test_create_competency_criterion_takes_the_tag_lock_itself (test_api.py:2013).
Nits
views.py:305-311: the view maps only DoesNotExist and ValidationError, so when a learner's grade write wins the race the delete's IntegrityError propagates as a 500, although a retry of the DELETE would archive the criterion correctly. Catch IntegrityError there and return a 409 with a message that says to retry, and update the delete docstring (api.py:1066-1071) to say so. The docstring also misses a third variant: a grade that commits between the status check at api.py:1085 and the collector's SELECT inside criterion.delete() at 1091 raises ProtectedError, a subclass of IntegrityError, so the same catch covers it.
test_criterion_removal.py:365 asserts the leaf and root are archived but not result.archived or the criterion; :444 asserts the result and history counts but not that the two archived groups still exist (the sibling at :497 does); :527 builds a live criterion under an archived leaf, which only the pre-#717 create path can produce, so make it the AC4 variant with archived=True on the criterion.
Comments and docstrings: the delete view's method docstring (views.py:292-301) can shrink to the file's one-line pattern plus "Archived rows still resolve, so a repeat DELETE on one returns 200"; the bulk update (api.py:711-713) and group PATCH (api.py:902-903) docstring paragraphs restate the inline comments beside the locks and can go; the delete docstring's three-races paragraph is the "why a lock, not a constraint" justification AGENTS.md asks for and reads better as an inline comment at the lock on api.py:1082, leaving the docstring to say who waits and what a lost grade race does; in _cascade_from_group() (api.py:964) "collapsing/archiving" should read "deleting or archiving", the "harmless" paragraph can go, and since the function walks upward and may archive, a name like _cascade_remove_from_group would say what it does.
PR body, Deviations: "#815 (rollup) and #816 (grade recording) own excluding archived rows from evaluation" is out of date. record_graded_object_statuses() already filters archived=False on main (api.py:819), so only the rollup still counts archived children.
Checks run locally at 3bb7e6d: clean merge onto current main, no migration changes, import linter green, 618 SQLite tests passing with the 10 MySQL-only tests skipped (no Docker here), pylint and mypy clean on the touched files.
@jesperhodge
All eight addressed: the deadlock claims are now scoped to the CBE authoring writers with the cascade deletes named as the exception, the lock-order and 'only one explicit lock' wordings are fixed, the grade-race test docstrings mention the 1213 variant, AC6 got the shared-ObjectTag parametrization, and the stray serializer_class is gone.
@mgwozdz-unicon
Done across the board: three ADR amendments reverted and Decision 7 uses your wording; 401 and parametrized 403 tests added; the create-path lock keeps one sentence explaining it guards a future direct caller; the delete view now maps IntegrityError (ProtectedError included) to a 409 asking to retry, with a real ProtectedError test; the three assertion gaps are closed; the prose trims and the _cascade_remove_from_group rename are in; the PR body's #816 line is corrected. The CBE-owned lock row follow-up ticket is drafted and will be filed as low priority.
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Sorry for the slow answer on the two questions from last week.
Fine with keeping the Tag lock for now plus a follow-up issue, or should we switch?
Please keep the Tag lock for create and delete in this PR, and please link the follow-up issue here before merging. I agree with @mgwozdz-unicon that the follow-up is low priority.
on hard delete we remove the criterion's ObjectTag row directly via the ORM, and we can't tell whether the author also tagged that content by hand. OK with you?
Yes, given that competency tags are only applied through the criteria endpoints for MVP.
From this review pass:
I have questions inline about whether bulk update and the group PATCH still need the lock on Tag. I won't hold the merge on it.
A question inline about what archiving the course-level group means for authors once #717 lands. No code change asked for.
A test nit, optional.
Please update the PR description: "Supporting information" and the last "Other information" bullet still list four ADR amendments, and the diff now only touches ADR-0002 Decision 7 and ADR-0004 Decision 6.
Thank you.
Claude assistance
Claude drafted this review and ran the following for me on bef27f6: the CBE suite on SQLite (621 passed, 10 skipped), `test_criterion_concurrency.py` against MySQL 8 three times (10 passed each time), and a trial merge with current `main` (clean; 631 passed on MySQL). The two probes described inline were also run by Claude; they were throwaway test files and aren't in the branch.
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Question: does bulk update need the Tag lock at all? Likewise for the group PATCH on line 932.
The deadlock against the delete came from the two select_for_update()s that this PR removes below, and I think removing them was the whole fix. Claude changed this line and line 932 to plain Tag.objects.get(...) and re-ran the delete-vs-bulk-update and delete-vs-PATCH races from test_criterion_concurrency.py on MySQL 8, in both the hard-delete and archive variants. None of the four deadlocked: each writer still waits for the delete, because it's blocked on the row it's about to UPDATE. What changes is what the loser gets afterwards:
After a hard delete, save(update_fields=...) raises DatabaseError: Save with update_fields did not affect any rows. instead of DoesNotExist.
After an archive, the edit lands on the row that was just archived.
Neither loses anything, and the first is one except DatabaseError away from the 404 you have now.
That being said, if there's a case where the unlocked version does real damage that I'm not seeing, please let me know.
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Actually, looking back at this this morning, never mind this suggestion. It's not necessary for the deadlock, but there's probably a higher chance of writing some garbage in a race, and it's not worth the trouble to rework at this point.
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Question: is the authoring side ready for how far this reaches? Claude ran this sequence on this branch: create a criterion, add a learner status row for it, DELETE it, then create a criterion for a different subsection under the same competency and course. The first three steps leave the leaf, the course-level group, and the root all archived. The second create succeeds into a new leaf under the archived course-level group, and a bulk update of that new criterion is refused with "Criteria under an archived group cannot be edited: group 2."
The description has that as waiting on #717, but #717 turns the second create into a rejection. So removing the last in-use criterion for a competency in a course means that competency can't be measured in that course again. I know ADR-0002 Decision 7 makes archiving permanent for MVP, so I'm not asking for a change here. I'd just like #710's confirmation step to say so, and #717 to merge before the UI can reach this endpoint.
The delete confirmations are added in #786 (PR AShatsila/frontend-app-authoring#15), and currently it just says that the removal can't be undone and that learners keep their mastery status, but it doesn't mention that removing the last in-use criterion for a competency in a course means that competency can't be associated with content in that course again. Tammie and I can update the ticket and PR to add messaging to that effect.
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Nit (optional): the SQLite tests built on this fixture pin that Tag.objects.select_for_update is the call being made, so they'll all need rewriting when the follow-up moves the lock off the Tag row. The MySQL tests assert outcomes and will survive that, so I'd lean on those and not add more of these.
@ormsbee follow-up issue for moving the per-competency lock off the Tag row: #935, filed as low priority per the thread. The description is also updated per your point 4
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Walkthrough
The change adds a public API and REST endpoint to delete or archive competency criteria. It coordinates criterion authoring and removal with competency-tag locks, removes or archives empty groups, and adds tests for removal, endpoint responses, and concurrent operations.
Criterion creation, bulk updates, and group updates coordinate through the competency-tag lock. Bulk updates save criteria in ascending ID order while preserving request order in their results. Decision records clarify which learner-status records protect data and which writers the lock rule covers.
Deletion, archival, and group cleanup src/openedx_learning/applets/cbe/api.py, src/openedx_learning/applets/cbe/data.py, tests/openedx_learning/applets/cbe/test_criterion_removal.py, tests/openedx_learning/applets/cbe/test_criterion_concurrency.py
The public API deletes criteria without learner status and archives criteria with learner status. It removes unreferenced tags and deletes or archives empty groups based on their contents and learner-status references. Tests cover cleanup, history attribution, and concurrent operations.
A tag-scoped DELETE endpoint returns the criterion ID and archived state. The serializer includes a read-only archived field. The view maps missing records to 404, validation errors to 400, and integrity conflicts to a retryable 409.
sequenceDiagram
participant Client
participant CompetencyCriterionDeleteView
participant delete_or_archive_competency_criterion
participant Database
Client->>CompetencyCriterionDeleteView: DELETE with tag ID and criterion ID
CompetencyCriterionDeleteView->>delete_or_archive_competency_criterion: Delete or archive criterion
delete_or_archive_competency_criterion->>Database: Lock tag and check learner status
Database-->>delete_or_archive_competency_criterion: Criterion and status records
delete_or_archive_competency_criterion-->>CompetencyCriterionDeleteView: Criterion ID and archived state
CompetencyCriterionDeleteView-->>Client: HTTP 200 with result
After a course-level group is archived by a criterion deletion, a later association can succeed but create a criterion that never appears in live discovery and cannot be edited. Reject archived ancestors on the create path before merging.
Security architecture risk: Low · up to 2a123
The new delete endpoint applies the same object-tagging permission the existing create and update paths use, and checks it before changing anything. Learner progress is never deleted: a criterion or group that learners have progress on is archived instead. Concurrent authoring is serialized on one per-competency lock. If a learner's grade lands during a delete, the delete is rolled back with a retryable conflict, so no data is lost silently. The remaining risk is small: an authenticated caller who lacks permission gets "not found" for an unknown criterion and "forbidden" for an existing one, which reveals which criterion IDs exist, and permission comes from an existing rule that this PR does not change.
Retained concerns
No architecture-level concerns identified.
Security review details
Security Blast Radius
observed — An authorized caller can affect only the target criterion, its own ObjectTag (when nothing else references it), and ancestor groups that are empty or hold only archived children. Learner status rows are never deleted, and any group with group-level status is archived rather than deleted.
Security Findings and Attack Paths
observed — The view resolves the criterion by ID and URL tag before the permission check. An authenticated user without permission therefore gets 404 for a nonexistent ID and 403 for an existing one, which reveals whether a criterion ID exists. It discloses nothing else and allows no writes.
Trust Boundaries and Controls
inferred — The permission subject (taxonomy and object_id) is read before the lock, while the mutation acts on a re-read made under the lock. Per the code comment a group's tag never changes, and I found no writer that reassigns a criterion's group or object_tag, so the authorized subject should equal the mutated subject. This was not exhaustively proven.
Resilience and Maintainability Implications
observed — All writers of a competency's criteria now take a single lock first, the competency Tag row. That ordering prevents the deadlocks and silent cascade deletions that the code comments describe for concurrent create and delete.
Hardening Proposals
proposed — Consider returning the same status for "not found" and "not permitted", or checking a tag-level permission before resolving the criterion, so the endpoint no longer reveals which criterion IDs exist.
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The title "feat: add endpoint to delete or archive a CompetencyCriterion (#674)" names the main change. The PR adds a DELETE endpoint that hard-deletes a competency criterion without learner-status re…
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Issue #674 is the only directly linked issue. Its coding requirements are met by the reviewed change set, as shown by the summaries of the diff and tests. (1) Endpoint: CompetencyCriterionDeleteView…
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The changes fall within #674 or are justified by it. (a) The delete function, view, URL, CriterionDeletionResult, and the archived serializer field implement the issue directly. (b) Locking change…
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The title "feat: add endpoint to delete or archive a CompetencyCriterion (#674)" names the main change. The PR adds a DELETE endpoint that hard-deletes a competency criterion without learner-status records, or archives it when such records exist. The title is specific and matches the linked issue #674. It does not cover the lock changes, ADR edits, or bulk-update ordering, which is acceptable.
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Issue #674 is the only directly linked issue. Its coding requirements are met by the reviewed change set, as shown by the summaries of the diff and tests. (1) Endpoint: CompetencyCriterionDeleteView is routed at DELETE /api/cbe/v1/competencies/<tag_id>/criteria/<criterion_id>/, which is tag-scoped. The PR states this is a deliberate deviation from the group-scoped URL in the issue, and it matches the caller in #710. (2) 404: missing criteria and tag/criterion mismatches return 404, and tests cover them. (3) 403: delete_or_archive_competency_criterion checks oel_tagging.can_tag_object before locking, and tests cover denial. (4) Hard delete: with no StudentCompetencyCriterionStatus, the row is deleted. Its ObjectTag is deleted only when no other CompetencyCriterion references it, and tests cover shared and unrelated tags. (5) Archive: with learner status, archived=True is set and the ObjectTag is left in place. (6) Repeat delete: archived rows return the same 200 body. If the learner status is gone, the row is hard-deleted, and a later request returns 404. (7) Group cascade: emptied ancestor groups are hard-deleted, or archived when StudentCompetencyCriteriaGroupStatus references them. Tests cover stopping at active content and at archived groups. (8) Response: 200 {id, archived} is returned through the read-only archived serializer field. Remaining uncertainty: the summaries do not show the archived-children-only branch in full code, so this rests on the test names and summaries, not on direct inspection of api.py.
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Explanation
The changes fall within #674 or are justified by it. (a) The delete function, view, URL, CriterionDeletionResult, and the archived serializer field implement the issue directly. (b) Locking changes in bulk_update_competency_criteria, update_competency_criteria_group, and create_competency_criterion serialize authoring with the delete. The PR states that the old lock shapes could deadlock with the delete cascade, so these changes support the delete's correctness. (c) The Tag.DoesNotExist to 404 mapping and the IntegrityError to 409 mapping are error handling for the delete race. (d) The ADR-0002 and ADR-0004 amendments document the delete and locking behavior that this PR introduces. The ADR text is documentation, not code, and the PR records its changelog entries. (e) The tests support the listed requirements. Out-of-scope items named in the issue, such as direct group deletion, Studio warnings, and criterion listing, are not in the summaries. The PR also leaves #717, #815, #817, and #935 as separate follow-up work, and it does not implement them here.
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Review comments at @src/openedx_learning/applets/cbe/api.py:
- Line 505: In associate_competency_criterion(), after locking the group’s Tag,
re-read its ancestry and reject the association if any course-level group is
archived, before calling tag_object(). Preserve the MVP behavior that archived
course-level groups block new associations; do not reactivate them.
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…x#674)
DELETE /api/cbe/v1/competencies/<tag_id>/criteria/<criterion_id>/
hard-deletes a criterion that no learner mastery status references,
and archives it in place otherwise, so recorded learner progress stays
intact and auditable. The response is 200 {"id", "archived"} in both
cases, and a repeat DELETE on an archived row returns the same body.
On a hard delete, the criterion's own ObjectTag row is removed, and
only while no other criterion references it; no other tag on the
object is touched. The archive path never touches the ObjectTag.
Groups left with no children by the delete are cascaded: each emptied
ancestor is hard-deleted, or archived when a learner group-status row
references it or when only archived children remain, in the same
transaction, so no empty group persists (ADR-0002 Decision 2).
Every writer of a competency's criteria follows one concurrency rule:
take the competency's Tag row lock first, read mutable state only
after it, take no other explicit lock, and save criteria in ascending
primary-key order. Bulk update drops its group and criteria
select_for_update() calls in favor of that lock, closing a deadlock
against the delete (MySQL error 1213), and the group PATCH re-reads
the group under the lock, so losing a race to the delete yields a 404
or an archived-conflict error instead of a DatabaseError. A grade
write that races a hard delete fails one side with an IntegrityError,
never silently; the delete view maps it to a retryable 409.
A MySQL-only two-connection test file exercises the lock across the
request, a waiting create, sibling deletes, the delete against bulk
update and the group PATCH, and the grade race in both orderings.
SQLite lock-point tests pin that each writer reads after taking the
lock. ADR-0002 Decision 7 and ADR-0004 Decision 6 are amended with
changelog entries. The follow-up for moving the lock off the shared
Tag row is openedx#935.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Mary Gwozdz <mgwozdz@unicon.net>
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Description
Adds a
DELETEendpoint that removes aCompetencyCriterion(the association between a gradeable object and a competency in a criteria tree). When no learner mastery status references the criterion, the row is hard-deleted; when one does, the row is archived in place (archived=True), so learner progress already recorded against it stays intact and auditable. The response is200 {"id": ..., "archived": false|true}in both cases, and a repeatDELETEon an archived row returns the same body again.Untagging. On a hard delete, the criterion's own
ObjectTagrow is deleted directly through the ORM, and only when no otherCompetencyCriterionstill references it (the same tagged object can be used in two different groups). No otherObjectTagon the object is touched. The archive path never touches theObjectTag.Group cascade. Removing a criterion can leave its leaf
CompetencyCriteriaGroup, and ancestors above it, with no children. The delete walks the ancestor chain and hard-deletes each emptied group, or archives it when aStudentCompetencyCriteriaGroupStatusrow references it, so no empty group persists (ADR-0002 Decision 2). The delete-vs-archive choice, for the criterion and for each cascaded group, is a server-side decision driven entirely by learner-status presence.Concurrency. Every writer of a competency's criteria now follows one rule: take that competency's
Tagrow lock first, read mutable state only after it, take no other group or criterion row lock, and save criteria in ascending primary-key order. The delete takes that lock around the re-read, the learner-status check, and the cascade. This PR also moves the two existing writers that predate it onto the same rule, because the old shapes could deadlock against the delete (the delete held the criterion row and waited for the leaf group, while a bulk update held the group rows and waited for the criterion, an unhandledOperationalError1213 on MySQL):bulk_update_competency_criteriadrops its twoselect_for_update()calls (group lineage and criteria) in favor of the Tag lock, runs its archived and membership checks after the lock, and saves in primary-key order, the same order in which the grading write locks criterion rows.update_competency_criteria_grouptakes the Tag lock and re-reads the group under it, so racing a delete now yields a clean 404 or archived-conflict error instead of aDatabaseErroror a silent write onto an archived group.A grade write that races a hard delete fails one side with an
IntegrityError, never silently: if the status insert commits first, the delete fails its foreign-key check and a second click archives the criterion; if the delete commits first, the grade's insert fails inside the learner's transaction. The delete docstring records this, the three races the Tag lock prevents, and the READ COMMITTED assumption.Tests. A new MySQL-only test file,
test_criterion_concurrency.py, exercises the locks over two database connections: the Tag lock held across the request, a create waiting and surviving, two sibling deletes leaving no empty leaf, delete racing bulk update (the old deadlock, now a clean error), delete racing the group PATCH, and grade-write-vs-delete in both orderings. The file skips on SQLite, whereselect_for_updateis a no-op, and runs in CI's MySQL job. Lock-point tests that run on SQLite pin each writer's lock: that the delete, bulk update and group update read current state only after taking it, and thatcreate_competency_criteriontakes it at all. The pk-ordered save loop is pinned by a SQLite call-order test; no MySQL test observes the lock order itself.This change affects the Course Author / Platform Administrator roles (correcting or retiring a mastery rule). It is a backend API addition; the Studio UI that calls it (#710) is separate.
Supporting information
main, which already carries the learner-status models (StudentCompetencyCriterionStatus,StudentCompetencyCriteriaGroupStatus) and the create endpoint ([BE] Create CompetencyCriteria #665) with thearchivedfields ([BE] Add archived field to Competency Criteria & Group models #716) this endpoint relies on.Testing instructions
POST /api/cbe/v1/competencies/<tag_id>/criteria/to create a criterion (see [BE] Create CompetencyCriteria #665).DELETE /api/cbe/v1/competencies/<tag_id>/criteria/<criterion_id>/:200 {"id": ..., "archived": false}, row gone, emptied groups gone.200 {"id": ..., "archived": true}, row present and archived.DELETEon the archived row → the same200body again.DELETEafter a hard delete, a mismatchedtag_id, or an unknowncriterion_id→404.oel_tagging.can_tag_objectfor the criterion's tagged object (the usage key stored in itsObjectTag.object_id) →403.python manage.py shell:Deadline
None.
Other information
Deviations from the ticket and the ADRs, each deliberate:
tag_id, not by group id, because the Studio caller ([FE] Manage & Apply Competencies: delete a Competency Criteria Association #710) has the tag and criterion ids but no group id. The URL name iscriterion-delete.archivednow appears in the create and bulk-update responses, as a read-only field.main; [BE] Exclude archived criteria and groups when rolling up a learner's competency status #815 owns excluding archived rows from the rollup. This PR is the first code that archives these rows.StudentCompetencyCriteriaGroupStatusdirectly before a group hard-delete. ADR-0004 Decision 6's no-lock rule is narrowed to learner-status writers, since the authoring writers serialize on theTagrow. Both amendments carry changelog entries; the empty-group enforcement and the archived criterion's liveObjectTagstay within the existing ADR text (theObjectTagis ultimately handled by [BE] Stop an assignment showing as tagged when the last competency rule measuring it is archived #817).No new model fields or migrations. Not in scope here (left to #675, the group-level counterpart): deleting or archiving a
CompetencyCriteriaGroupdirectly, and the Studio in-use warning/confirmation flow ADR-0003 Decision 4 requires before calling this endpoint.🤖 Generated with Claude Code
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