Common recipes

Note

Most recipes below take on Django model examples, but can also be used on their own.

Dependent objects (ForeignKey)

When one attribute is actually a complex field (e.g a ForeignKey to another Model), use the SubFactory declaration:

# models.py
class User(models.Model):
    first_name = models.CharField()
    group = models.ForeignKey(Group)


# factories.py
import factory
from . import models

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.User

    first_name = factory.Sequence(lambda n: "Agent %03d" % n)
    group = factory.SubFactory(GroupFactory)

Reverse dependencies (reverse ForeignKey)

When a related object should be created upon object creation (e.g a reverse ForeignKey from another Model), use a RelatedFactory declaration:

# models.py
class User(models.Model):
    pass

class UserLog(models.Model):
    user = models.ForeignKey(User)
    action = models.CharField()


# factories.py
class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.User

    log = factory.RelatedFactory(UserLogFactory, 'user', action=models.UserLog.ACTION_CREATE)

When a UserFactory is instantiated, factory_boy will call UserLogFactory(user=that_user, action=...) just before returning the created User.

Example: Django’s Profile

Django (<1.5) provided a mechanism to attach a Profile to a User instance, using a OneToOneField from the Profile to the User.

A typical way to create those profiles was to hook a post-save signal to the User model.

factory_boy allows to define attributes of such profiles dynamically when creating a User:

class ProfileFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = my_models.Profile

    title = 'Dr'
    # We pass in profile=None to prevent UserFactory from creating another profile
    # (this disables the RelatedFactory)
    user = factory.SubFactory('app.factories.UserFactory', profile=None)

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = auth_models.User

    username = factory.Sequence(lambda n: "user_%d" % n)

    # We pass in 'user' to link the generated Profile to our just-generated User
    # This will call ProfileFactory(user=our_new_user), thus skipping the SubFactory.
    profile = factory.RelatedFactory(ProfileFactory, 'user')

    @classmethod
    def _generate(cls, create, attrs):
        """Override the default _generate() to disable the post-save signal."""

        # Note: If the signal was defined with a dispatch_uid, include that in both calls.
        post_save.disconnect(handler_create_user_profile, auth_models.User)
        user = super(UserFactory, cls)._generate(create, attrs)
        post_save.connect(handler_create_user_profile, auth_models.User)
        return user
>>> u = UserFactory(profile__title=u"Lord")
>>> u.get_profile().title
u"Lord"

Such behaviour can be extended to other situations where a signal interferes with factory_boy related factories.

Note

When any RelatedFactory or post_generation attribute is defined on the DjangoModelFactory subclass, a second save() is performed after the call to _create().

Code working with signals should thus override the _generate() method.

Simple ManyToMany

Building the adequate link between two models depends heavily on the use case; factory_boy doesn’t provide a “all in one tools” as for SubFactory or RelatedFactory, users will have to craft their own depending on the model.

The base building block for this feature is the post_generation hook:

# models.py
class Group(models.Model):
    name = models.CharField()

class User(models.Model):
    name = models.CharField()
    groups = models.ManyToMany(Group)


# factories.py
class GroupFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Group

    name = factory.Sequence(lambda n: "Group #%s" % n)

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.User

    name = "John Doe"

    @factory.post_generation
    def groups(self, create, extracted, **kwargs):
        if not create:
            # Simple build, do nothing.
            return

        if extracted:
            # A list of groups were passed in, use them
            for group in extracted:
                self.groups.add(group)

When calling UserFactory() or UserFactory.build(), no group binding will be created.

But when UserFactory.create(groups=(group1, group2, group3)) is called, the groups declaration will add passed in groups to the set of groups for the user.

ManyToMany with a ‘through’

If only one link is required, this can be simply performed with a RelatedFactory. If more links are needed, simply add more RelatedFactory declarations:

# models.py
class User(models.Model):
    name = models.CharField()

class Group(models.Model):
    name = models.CharField()
    members = models.ManyToMany(User, through='GroupLevel')

class GroupLevel(models.Model):
    user = models.ForeignKey(User)
    group = models.ForeignKey(Group)
    rank = models.IntegerField()


# factories.py
class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.User

    name = "John Doe"

class GroupFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Group

    name = "Admins"

class GroupLevelFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.GroupLevel

    user = factory.SubFactory(UserFactory)
    group = factory.SubFactory(GroupFactory)
    rank = 1

class UserWithGroupFactory(UserFactory):
    membership = factory.RelatedFactory(GroupLevelFactory, 'user')

class UserWith2GroupsFactory(UserFactory):
    membership1 = factory.RelatedFactory(GroupLevelFactory, 'user', group__name='Group1')
    membership2 = factory.RelatedFactory(GroupLevelFactory, 'user', group__name='Group2')

Whenever the UserWithGroupFactory is called, it will, as a post-generation hook, call the GroupLevelFactory, passing the generated user as a user field:

  1. UserWithGroupFactory() generates a User instance, obj
  2. It calls GroupLevelFactory(user=obj)
  3. It returns obj

When using the UserWith2GroupsFactory, that behavior becomes:

  1. UserWith2GroupsFactory() generates a User instance, obj
  2. It calls GroupLevelFactory(user=obj, group__name='Group1')
  3. It calls GroupLevelFactory(user=obj, group__name='Group2')
  4. It returns obj

Copying fields to a SubFactory

When a field of a related class should match one of the container:

# models.py
class Country(models.Model):
    name = models.CharField()
    lang = models.CharField()

class User(models.Model):
    name = models.CharField()
    lang = models.CharField()
    country = models.ForeignKey(Country)

class Company(models.Model):
    name = models.CharField()
    owner = models.ForeignKey(User)
    country = models.ForeignKey(Country)

Here, we want:

  • The User to have the lang of its country (factory.SelfAttribute('country.lang'))
  • The Company owner to live in the country of the company (factory.SelfAttribute('..country'))
# factories.py
class CountryFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Country

    name = factory.Iterator(["France", "Italy", "Spain"])
    lang = factory.Iterator(['fr', 'it', 'es'])

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.User

    name = "John"
    lang = factory.SelfAttribute('country.lang')
    country = factory.SubFactory(CountryFactory)

class CompanyFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Company

    name = "ACME, Inc."
    country = factory.SubFactory(CountryFactory)
    owner = factory.SubFactory(UserFactory, country=factory.SelfAttribute('..country'))

Custom manager methods

Sometimes you need a factory to call a specific manager method other then the default Model.objects.create() method:

class UserFactory(factory.DjangoModelFactory):
    class Meta:
        model = UserenaSignup

    username = "l7d8s"
    email = "my_name@example.com"
    password = "my_password"

    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        """Override the default ``_create`` with our custom call."""
        manager = cls._get_manager(model_class)
        # The default would use ``manager.create(*args, **kwargs)``
        return manager.create_user(*args, **kwargs)

Forcing the sequence counter

A common pattern with factory_boy is to use a factory.Sequence declaration to provide varying values to attributes declared as unique.

However, it is sometimes useful to force a given value to the counter, for instance to ensure that tests are properly reproductible.

factory_boy provides a few hooks for this:

Forcing the value on a per-call basis

In order to force the counter for a specific Factory instantiation, just pass the value in the __sequence=42 parameter:

class AccountFactory(factory.Factory):
    class Meta:
        model = Account
    uid = factory.Sequence(lambda n: n)
    name = "Test"
>>> obj1 = AccountFactory(name="John Doe", __sequence=10)
>>> obj1.uid  # Taken from the __sequence counter
10
>>> obj2 = AccountFactory(name="Jane Doe")
>>> obj2.uid  # The base sequence counter hasn't changed
1
Resetting the counter globally

If all calls for a factory must start from a deterministic number, use factory.Factory.reset_sequence(); this will reset the counter to its initial value (as defined by factory.Factory._setup_next_sequence()).

>>> AccountFactory().uid
1
>>> AccountFactory().uid
2
>>> AccountFactory.reset_sequence()
>>> AccountFactory().uid  # Reset to the initial value
1
>>> AccountFactory().uid
2

It is also possible to reset the counter to a specific value:

>>> AccountFactory.reset_sequence(10)
>>> AccountFactory().uid
10
>>> AccountFactory().uid
11

This recipe is most useful in a TestCase‘s setUp() method.

Forcing the initial value for all projects

The sequence counter of a Factory can also be set automatically upon the first call through the _setup_next_sequence() method; this helps when the objects’s attributes mustn’t conflict with pre-existing data.

A typical example is to ensure that running a Python script twice will create non-conflicting objects, by setting up the counter to “max used value plus one”:

class AccountFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Account

    @classmethod
    def _setup_next_sequence(cls):
        try:
            return models.Accounts.objects.latest('uid').uid + 1
        except models.Account.DoesNotExist:
            return 1
>>> Account.objects.create(uid=42, name="Blah")
>>> AccountFactory.create()  # Sets up the account number based on the latest uid
<Account uid=43, name=Test>