Opened 13 days ago
Last modified 13 days ago
#35381 new Bug
Regression on json null value constraints in django 4.2
Reported by: | Olivier Tabone | Owned by: | nobody |
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Component: | Database layer (models, ORM) | Version: | 5.0 |
Severity: | Normal | Keywords: | |
Cc: | David Sanders, Simon Charette, Mariusz Felisiak | Triage Stage: | Accepted |
Has patch: | no | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
Regression is still present in 5.0 and main branch
given a model defined as follow
from django.db import models class JSONFieldModel(models.Model): data = models.JSONField(null=True, blank=True, default=None) class Meta: required_db_features = {"supports_json_field"} constraints = [ models.CheckConstraint( check=~models.Q(data=models.Value(None, models.JSONField())), name="json_data_cant_be_json_null", ), ]
the following test works in django 4.1.13, fails in later version
from django.test import TestCase, skipUnlessDBFeature from .models import JSONFieldModel class CheckConstraintTests(TestCase): @skipUnlessDBFeature("supports_json_field") def test_full_clean_on_null_value(self): instance = JSONFieldModel.objects.create(data=None) # data = SQL Null value instance.full_clean()
tests/runtests.py json_null_tests ====================================================================== ERROR: test_full_clean_on_null_value (json_null_tests.tests.CheckConstraintTests.test_full_clean_on_null_value) ---------------------------------------------------------------------- Traceback (most recent call last): File "/Users/olivier/dev/django.dev/olibook/django/django/test/testcases.py", line 1428, in skip_wrapper return test_func(*args, **kwargs) ^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/olivier/dev/django.dev/olibook/django/tests/json_null_tests/tests.py", line 13, in test_full_clean_on_null_value instance.full_clean() File "/Users/olivier/dev/django.dev/olibook/django/django/db/models/base.py", line 1504, in full_clean raise ValidationError(errors) django.core.exceptions.ValidationError: {'__all__': ['Constraint “json_data_cant_be_json_null” is violated.']} ----------------------------------------------------------------------
Attached a patch that will create run json_null_tests folder in django's tests
directories. Test can be run with
tests/runtests.py json_null_tests
NOTE : in django 5.1 the CheckConstraint.check
parameter as been renamed to CheckConstraint.condition
.
I ran a git bisect on this test case:
8fcb9f1f106cf60d953d88aeaa412cc625c60029 is bad
e14d08cd894e9d91cb5d9f44ba7532c1a223f458 is good
git bisect run tests/runtests.py json_null_tests
5c23d9f0c32f166c81ecb6f3f01d5077a6084318 is identified as first bad commit
the issue appears with both sqlite and postgres backends
A few words on what we I'm trying to achieve (some context on the regression):
The json_data_cant_be_json_null
aims to prevent having JsonModel.data = None
(SQL Null) and JSONModel.data = Value(None, JSONField())
(JSON null) values in the database. These leads to unwanted behaviors when filtering on the null value, and I settled on representing the absence of value with SQL Null and not JSON null.
The app was running in django 4.1 and I'm upgrading it to later django version. That's how the issue appeared.
Attachments (1)
Change History (3)
by , 13 days ago
Attachment: | json_null_tests.patch added |
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comment:1 by , 13 days ago
Cc: | added |
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Triage Stage: | Unreviewed → Accepted |
Type: | Uncategorized → Bug |
I think this is related to #34754, and I originally thought that this was another consequence of what Simon said there: I think the fundamental problem here is that:
but then I ran the proposed test with
--debug-sql
(and postgres) and noticed that the check code is casting the value in the database to::JSONB
independently of whether the value isNone
or not:So I kept digging and bisected the "bad" commit to 5c23d9f0c32f166c81ecb6f3f01d5077a6084318, and something like this makes the test pass:
django/db/models/fields/json.py
hasattr(value, "as_sql"):it makes the test
model_fields.test_jsonfield.TestSaveLoad.test_json_null_different_from_sql_null
fails for the check on the query:So further investigation is needed to come up with an acceptable solution.