How to use lazy_attribute with Faker in Factory Boy

user_150647 0
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Context: I have a model with two dates, I want to use factory.Faker for both of them but the second date should always be greater that the first one.

I tried this:

Model excerpt:

class Event(models.Model):
     execution_start_date = models.DateTimeField()
     execution_end_date = models.DateTimeField()

Factory:

class EventFactory(factory.DjangoModelFactory):
    class Meta:
        model = Event
        strategy = factory.BUILD_STRATEGY

    execution_start_date = factory.Faker('date_time_this_year', tzinfo=pytz.utc)
    @factory.lazy_attribute
    def execution_end_date(self):
        return factory.Faker('date_time_between_dates',
                             datetime_start=self.execution_start_date,
                             datetime_end=now(),
                             tzinfo=pytz.utc)

But when I try to use the factory from the python shell I got this:

In [3]: e = EventFactory()

In [4]: e.execution_end_date
Out[4]: <factory.faker.Faker at 0x1103f51d0>

The only way I managed to make it work was with like this:

@factory.lazy_attribute
def execution_end_date(self):
    # return factory.Faker('date_time_between_dates',
    #                      datetime_start=self.execution_start_date,
    #                      datetime_end=now(),
    #                      tzinfo=pytz.utc)
    faker = factory.Faker._get_faker()
    return faker.date_time_between_dates(datetime_start=self.execution_start_date,
                                         datetime_end=now(),
                                         tzinfo=pytz.utc)

But I honestly think there is a better way to do it.

My dependencies are:

  • Django (1.8.18)
  • factory-boy (2.8.1)
  • Faker (0.7.17)
factory-boy faker django-models django python
2 Answers

At first I was trying to do the same thing, but according to Factory Boy's documentation for the Faker wrapper, the parameters can be any valid declaration. That means that you're allowed to specify each of the faker's parameter as a SelfAttribute, LazyAttribute, etc. I don't know when this feature was first introduced, but version 3.1.0 (Oct 2020) docs mentions it for the first time.

I believe that the question's example can be rewritten as:

class EventFactory(factory.DjangoModelFactory):
    class Meta:
        model = Event
        strategy = factory.BUILD_STRATEGY

    execution_start_date = factory.Faker('date_time_this_year', tzinfo=pytz.utc)
    execution_end_date = factory.Faker('date_time_between_dates',
                             datetime_start=factory.SelfAttribute('..execution_start_date'),
                             datetime_end='now',
                             tzinfo=pytz.utc)

So basically it's turned around and the faker's parameters are evaluated instead of the LazyAttribute's return value. In my example datetime_start now refers to whatever execution_start_date resolves to and datetime_end takes a literal string 'now', that the Faker library will replace with the current datetime.

user_32981750
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