flaeppe/django-traits

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.

class TestPerson:
    test_is_rich = test_trait(
        (
            (PersonFactory(), False),
            (PersonFactory(income=1000), False),
            (PersonFactory(income=1001), True),
        )
    )

The above example will generate tests that exercises the in-Python predicate on instances of Person, as well as tests that tries to filter using the ORM predicate. That means that 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.