#23741: [System Check for migrations] Check presence of all foreign keys
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Reporter: notsqrt | Owner: nobody
Type: Uncategorized | Status: new
Component: Core (System checks) | Version: 1.7
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hi !
Just had some troubles when upgrading to django 1.7, which led to some
discussions on https://groups.google.com/forum/#!topic/django-
users/x_7Fluj2ty8
The bottom line is : make sure that any app that depends on apps with
migrations also uses migrartions.
This is indeed stated in the docs :
https://docs.djangoproject.com/en/1.7/topics/migrations/#unmigrated-
dependencies
But the consequences are, I think, not sufficiently flagged.
One of the symptoms is that '''foreign key constraints won't be
created'''.
This ticket suggests two things:
* highlighting more clearly the consequences of not using migrations
(probably simply by putting that section in a "danger" block)
* adding a system check that all foreign keys are effectively enforced.
For the second point, it goes like:
{{{#!python
@checks.register()
def check_db_constraints(*args, **kwargs):
from django.apps import apps
from django.db import connection
from django.db.models.fields.related import RelatedField
errors = []
for model in apps.get_models():
if not model._meta.managed:
continue
relations =
connection.introspection.get_relations(connection.cursor(),
model._meta.db_table)
for field_id, field_info in
enumerate(model._meta.get_fields_with_model()):
field_model = field_info[0]
if isinstance(field_model, RelatedField):
if field_id not in relations:
errors.append(
checks.Error(
"Field %s of model %s has no detected database
relation." % (field_model, model.__name__),
hint="Check that the app has migrations if it
depends on apps that use them.",
)
)
return errors
}}}
It probably needs some refinements for multiple db connections and
detection of backends that do not support constraints.
--
Ticket URL: <https://code.djangoproject.com/ticket/23741>
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