#21134: Documentation for transaction.atomic needs more explicit warning about
catching DatabaseErrors
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Reporter: RichardOfWard | Owner: aaugustin
Type: | Status: new
Cleanup/optimization | Version:
Component: Documentation | 1.6-beta-1
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by aaugustin):
This pull request prevents running queries in `atomic` blocks that are
going to end with a rollback.
Since `atomic` is a new API, this change looks like it's backwards
compatible. Unfortunately, it isn't, because some features already take
advantage of `atomic` internally.
Specifically `django.test.TestCase` wraps each test in an `atomic` block.
As a consequence, tests that ran queries after database errors will
require modifications, even if the query is a rollback to a previous
savepoint. That said:
- If it's a test for transactional behavior, it should be in a
`TransactionTestCase`. Quite obviously high-level and low-level APIs
cannot be mixed arbitrarily.
- If the savepoint is used to recover from a database error, it's much
easier to recover with an `atomic` block. This is how I fixed the few
tests that were broken by this change in Django's test suite.
If we decide to go with this approach, I'll add this to the transactions
docs or the release notes.
--
Ticket URL: <https://code.djangoproject.com/ticket/21134#comment:6>
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