#23718: TEST_MIRROR setting doesn't work as expected (and has no tests)
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Reporter: Ilya Baryshev | Owner: Simon
| Charette
Type: Bug | Status: assigned
Component: Testing framework | Version: 1.7
Severity: Normal | Resolution:
Keywords: replica testing | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by pachewise):
Hi Team,
We also noticed an issue here which happens when you have a default +
read_replica config, and you have a router that only selects a
read_replica when considering particular models. If you have those
conditions, _and_ a data migration that uses both Job and User, you will
have issues because the "default" connection config will be pointing to
your `test_myschema`, whereas the `read_replica` config will still be
pointing to `myschema`.
e.g.,
{{{
models.py:
Job:
user_id := FK(User)
DBRouter:
db_for_write := 'read_replica' if model == Job else 'default'
settings:
DATABASES = {
'default': { ... },
'read_replica': {
# <configs>...
'TEST': {'MIRROR': 'default'}
}
}
0001_migration.py:
# ...
for job in Job.objects.all(): # using apps.get_model()
job.user.id # will error out with __fake__.DoesNotExist
}}}
In the case above, if your "live" read_replica schema has any job data, it
will try to run that last line, but there won't be any Users in the
`test_schema` to match to.
Not sure if ''we're'' doing something wrong, but just letting you know
that there are cases where a custom DBrouter could route to a config that
''should'' be a test mirror, but isn't.
Using python 3.6, Django 1.11.20, MySQL 5.7
--
Ticket URL: <https://code.djangoproject.com/ticket/23718#comment:23>
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