How to use a Faker value as part of another field with FactoryBoy

Question

I'm using FactoryBoy and Faker to generate some models for unit tests. Generating data for fields is easy enough, but how to I generate a string that incorporates a value produced from a Faker provider?

import factory
import MyModel

class MyFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = MyModel
        # my_ip will be a temporary variable that is not returned by the factory.
        exclude = (my_ip,)

    my_ip = factory.Faker("ipv4_private")
    my_string = f"String with IP address [{my_ip}]"

Using MyFactory then creates objects with my_string set to something like:

String with IP address [<factory.faker.Faker object at 0x7fc656aa6358>]

How can I get my_string to contain something like:

String with the IP address [192.168.23.112]

How do I resolve this to a value, rather than just getting the object? I've tried wrapping in str() with no luck. Do I need to use LazyAttribute or LazyFunction or something from FactoryBoy?

Carmina

Answer 1

With some trial and error I figured out this did require using LazyAttribute so the my_string attribute is calculated after the rest of the object is generated.

However, I then discovered this is essentially a duplicate of: In Factory Boy, how to join strings created with Faker?

If anyone is wondering, the way to do this is:

my_string = factory.LazyAttribute(lambda o: f"String with IP address [{o.my_ip}]")

Carmina

Answer 2

Use the Params feature of factory_boy to make the my_ip value available to LazyAttribute without factory_boy trying to set it on the model.

import factory
import MyModel

class MyFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = MyModel

    class Params:
        my_ip = factory.Faker("ipv4_private")

    my_string = factory.LazyAttribute(lambda o: f"String with IP address [{o.my_ip}]")

Drumfish