Fix the LMSCourse backfill from grouping migration #6612
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The existing LMSCourse has two assumptions, with one unique index for each: - The same course (same authority_provided_id) can belong to multiple applications instances but we'll keep only one row in LMSCourse for it (unique h_authority_provided_id) - authority_provided_id is generated from guid, lti_context_id, then, those two columns should also be unique together. There's however a case when this is not true: - Applications instance with a null GUID launches and creates a course (None, CONTEXT_ID). This generates a hashed authority_provided_id. - The same application instance (ie, same row in ApplicationInstance) starts sending a GUID. We calculate a new (GUID, CONTEXT_ID) hash creating a new course, with a different authority_provided_id. When we join with ApplicationInstance for the backfill we only have the most recent GUID and we end up creating (GUID, CONTEXT_ID) duplicates. The solution is to exclude this type of duplicate, which is safe because this only happens on: - GUID changes from null to not null. We don't allow other value changes for GUID. - We only deduplicate courses when we have a newer version of the course, the older one can no longer be launched, the ApplicationInstance now has a GUID and it will sent along with every launch.
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marcospri
commented
Aug 29, 2024
| @@ -13,21 +13,26 @@ def upgrade() -> None: | |||
| sa.text( | |||
| """ | |||
| WITH backfill as ( | |||
| -- Deduplicate "grouping" courses on authority_provided_id | |||
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This block is used verbatim, it just become a subquery.
marcospri
commented
Aug 29, 2024
| -- Pick the most recent "grouping" there are duplicates | ||
| ORDER BY authority_provided_id, "grouping".updated desc | ||
| -- Deduplicate on guid, lms_id | ||
| SELECT DISTINCT on (tool_consumer_instance_guid, lms_id) * |
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New, distinct on, (tool_consumer_instance_guid, lms_id)
seanh
approved these changes
Aug 29, 2024
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For:
The existing LMSCourse has two assumptions, with one unique index for each:
The same course (same authority_provided_id) can belong to multiple applications instances but we'll keep only one row in LMSCourse for it (unique h_authority_provided_id)
authority_provided_id is generated from guid, lti_context_id, then, those two columns should also be unique together.
There's however a case when this is not true:
Applications instance with a null GUID launches and creates a course (None, CONTEXT_ID). This generates a hashed authority_provided_id.
The same application instance (ie, same row in ApplicationInstance) starts sending a GUID. We calculate a new (GUID, CONTEXT_ID) hash creating a new course, with a different authority_provided_id.
When we join with ApplicationInstance for the backfill we only have the most recent GUID and we end up creating (GUID, CONTEXT_ID) duplicates.
The solution is to exclude this type of duplicate, which is safe because this only happens on:
GUID changes from null to not null. We don't allow other value changes for GUID.
We only deduplicate courses when we have a newer version of the course, the older one can no longer be launched, the ApplicationInstance now has a GUID and it will sent along with every launch.
Testing
The select side of the migration can be tested.
Note the two different rows for the same course with two different authority_provided_ids
The new query removes the duplicate, only taking most recent course.