These checks are causing SQL query numbers to scale linearly with the
number of subsections being created/updated, and the errors they
check for have not been seen in prod.
TNL-6225
Some old mongo courses do not have this field, and the team has opted
to allow null values rather than inserting a default. This change
affects both course and subsection grades.
TNL-6408
The column is populated with the current timestamp when a passing grade
is persisted for the first time. "Passing grade" is defined as having a
non-blank value for letter_grade.
TNL-5888
Small changes to the grades djangoapp
-sets up mock_get_score context handler
-fixes an issue with not invalidating lazy scores property
-code quality fixes
-query count optimization in PersistentSubscetionGrade.create
-adds atomic blocks to avoid IntegrityErrors corrupting an entire request
Hooks the pre-existing grades code into our new PersistentSubsectionGrade data
model. Includes test updates, and some minor changes to the data model that
were discovered in testing.
