django-traits
Define traits for Django models that works seamlessly both in-Python and using the ORM, with coordinated tests.
Installation
$ python3 -m pip install django-traits
Example
class Rich(Trait["Person"]):
q = models.Q(income__gt=1000)
def check_instance(self, instance: Person) -> bool:
return instance.income > 1000
class Person(models.Model):
is_rich = Rich()
income = models.PositiveIntegerField()
# Filter for rich people, this uses the ORM predicate as defined in q.
rich_people = Person.is_rich.all()
# Check if a person is rich, this uses the in-Python predicate as defined in check_instance().
person = Person.objects.first()
if person.is_rich:
print("Money is not a problem")
else:
print("This person is not rich")
The automated test factory makes it simple to write tests that guarantees that the in-Python predicate stays in sync with its ORM counterpart. The following example generates parameterized tests that checks boundary values.
import pytest
from traits.tests import create_trait_test
parametrize_people = pytest.mark.parametrize(
"instance",
PersonFactory(),
PersonFactory(income=1000),
PersonFactory(income=1001),
)
class TestPerson:
test_is_rich = parametrize_people(create_trait_test(Person.is_rich))
The above example will generate three tests that checks that each given instance of
Person
only appears in an ORM query result if the trait evaluates to True
for that
instance, and that the result set is empty if it evaluates to False
. So if the
implementations were to drift apart, for instance if the limit was increased to 2000
in check_instance()
but not in q
, the tests would fail and enforce that the two
implementations are in sync.
You can also use Hypothesis to automatically generate test values.
from traits.tests import create_trait_test
from hypothesis import given
from hypothesis.strategies import builds
from hypothesis.strategies import integers
people = builds(
PersonFactory.build,
income=integers(-9223372036854775808, 9223372036854775807),
)
class TestPerson:
test_is_rich = given(people)(create_trait_test(Person.is_rich))