I needed this change because I found a bug:
1. Create a block with children in a content library
2. Delete that content library
3. Create a new identical block with children in a new content library.
4. If the OLX is identical to the original block, this new block will not load in the LMS.
The reason for the bug is that the .children field contains usage keys (which encode the library, for example), but the values were being stored in BlockstoreFieldData which caches really aggressively and caches based on the hash of the OLX. Since the OLX is identical, it assumes the .children values should be identical as well.
The fix was to move children to a children-specific field data store, and only store the part of the child data that is encoded by the OLX (the <xblock-include> data) in BlockstoreFieldData. This is a better match for the way the caching works and cleaned up a hacky part of the runtime (at least it's slightly less hacky now).
This commit introduces the changes needed for XBlocks in Blockstore to save
their user state into CSM. Before this commit, all student state for Blockstore
blocks was ephemeral (in-process dict store).
Notes:
* The main risk factor of this PR is that it adds non-course keys to the
course_id field in CSM. If any code (like analytics?) reads course keys
directly out of CSM and doesn't have graceful handling for key types it
doesn't recognize, it could cause an issue. With the included changes to
opaque-keys, calling CourseKey.from_string(...) on these values will raise
InvalidKeyError since they're not CourseKeys. (But calling
LearningContextKey.from_string(...) will work for both course and library
keys.)
* This commit introduces a slight regression for the Studio view of XBlocks in
Blockstore content libraries: their state is now lost from request to request.
I have a follow up PR to give them a proper studio-appropriate state store,
but I want to review it separately so it doesn't hold up this PR and we can
test this PR on its own.
https://github.com/edx/edx-platform/pull/20645
This introduces:
* A new XBlock runtime that can read and write XBlocks that are persisted using
Blockstore instead of Modulestore. The new runtime is currently isolated so
that it can be tested without risk to the current courseware/runtime.
* Content Libraries v2, which store XBlocks in Blockstore not modulestore
* An API Client for Blockstore
* "Learning Context" plugin API. A learning context is a more abstract concept
than a course; it's a collection of XBlocks that serves some learning purpose.
