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Introduction
============
The purpose of factory_boy is to provide a default way of getting a new instance,
while still being able to override some fields on a per-call basis.
.. note:: This section will drive you through an overview of factory_boy's feature.
New users are advised to spend a few minutes browsing through this list
of useful helpers.
Users looking for quick helpers may take a look at :doc:`recipes`,
while those needing detailed documentation will be interested in the :doc:`reference` section.
Basic usage
-----------
Factories declare a set of attributes used to instantiate an object, whose class is defined in the ``class Meta``'s ``model`` attribute:
- Subclass ``factory.Factory`` (or a more suitable subclass)
- Add a ``class Meta:`` block
- Set its ``model`` attribute to the target class
- Add defaults for keyword args to pass to the associated class' ``__init__`` method
.. code-block:: python
import factory
from . import base
class UserFactory(factory.Factory):
class Meta:
model = base.User
firstname = "John"
lastname = "Doe"
You may now get ``base.User`` instances trivially:
.. code-block:: pycon
>>> john = UserFactory()
<User: John Doe>
It is also possible to override the defined attributes by passing keyword arguments to the factory:
.. code-block:: pycon
>>> jack = UserFactory(firstname="Jack")
<User: Jack Doe>
A given class may be associated to many :class:`~factory.Factory` subclasses:
.. code-block:: python
class EnglishUserFactory(factory.Factory):
class Meta:
model = base.User
firstname = "John"
lastname = "Doe"
lang = 'en'
class FrenchUserFactory(factory.Factory):
class Meta:
model = base.User
firstname = "Jean"
lastname = "Dupont"
lang = 'fr'
.. code-block:: pycon
>>> EnglishUserFactory()
<User: John Doe (en)>
>>> FrenchUserFactory()
<User: Jean Dupont (fr)>
Sequences
---------
When a field has a unique key, each object generated by the factory should have a different value for that field.
This is achieved with the :class:`~factory.Sequence` declaration:
.. code-block:: python
class UserFactory(factory.Factory):
class Meta:
model = models.User
username = factory.Sequence(lambda n: 'user%d' % n)
.. code-block:: pycon
>>> UserFactory()
<User: user1>
>>> UserFactory()
<User: user2>
.. note:: For more complex situations, you may also use the :meth:`~factory.@sequence` decorator (note that ``self`` is not added as first parameter):
.. code-block:: python
class UserFactory(factory.Factory):
class Meta:
model = models.User
@factory.sequence
def username(n):
return 'user%d' % n
LazyAttribute
-------------
Some fields may be deduced from others, for instance the email based on the username.
The :class:`~factory.LazyAttribute` handles such cases: it should receive a function
taking the object being built and returning the value for the field:
.. code-block:: python
class UserFactory(factory.Factory):
class Meta:
model = models.User
username = factory.Sequence(lambda n: 'user%d' % n)
email = factory.LazyAttribute(lambda obj: '%s@example.com' % obj.username)
.. code-block:: pycon
>>> UserFactory()
<User: user1 (user1@example.com)>
>>> # The LazyAttribute handles overridden fields
>>> UserFactory(username='john')
<User: john (john@example.com)>
>>> # They can be directly overridden as well
>>> UserFactory(email='doe@example.com')
<User: user3 (doe@example.com)>
.. note:: As for :class:`~factory.Sequence`, a :meth:`~factory.@lazy_attribute` decorator is available:
.. code-block:: python
class UserFactory(factory.Factory):
class Meta:
model = models.User
username = factory.Sequence(lambda n: 'user%d' % n)
@factory.lazy_attribute
def email(self):
return '%s@example.com' % self.username
Inheritance
-----------
Once a "base" factory has been defined for a given class,
alternate versions can be easily defined through subclassing.
The subclassed :class:`~factory.Factory` will inherit all declarations from its parent,
and update them with its own declarations:
.. code-block:: python
class UserFactory(factory.Factory):
class Meta:
model = base.User
firstname = "John"
lastname = "Doe"
group = 'users'
class AdminFactory(UserFactory):
admin = True
group = 'admins'
.. code-block:: pycon
>>> user = UserFactory()
>>> user
<User: John Doe>
>>> user.group
'users'
>>> admin = AdminFactory()
>>> admin
<User: John Doe <User: John Doe (admin)>
>>> admin.group # The AdminFactory field has overridden the base field
'admins'
Any argument of all factories in the chain can easily be overridden:
.. code-block:: pycon
>>> super_admin = AdminFactory(group='superadmins', lastname="Lennon")
>>> super_admin
<User: John Lennon (admin)>
>>> super_admin.group # Overridden at call time
'superadmins'
Non-kwarg arguments
-------------------
Some classes take a few, non-kwarg arguments first.
This is handled by the :data:`~factory.FactoryOptions.arg_parameters` attribute:
.. code-block:: python
class MyFactory(factory.Factory):
class Meta:
model = MyClass
arg_parameters = ('x', 'y')
x = 1
y = 2
z = 3
.. code-block:: pycon
>>> MyFactory(y=4)
<MyClass(1, 4, z=3)>
Strategies
----------
All factories support two built-in strategies:
* ``build`` provides a local object
* ``create`` instantiates a local object, and saves it to the database.
.. note:: For 1.X versions, the ``create`` will actually call ``AssociatedClass.objects.create``,
as for a Django model.
Starting from 2.0, :meth:`factory.Factory.create` simply calls ``AssociatedClass(**kwargs)``.
You should use :class:`~factory.django.DjangoModelFactory` for Django models.
When a :class:`~factory.Factory` includes related fields (:class:`~factory.SubFactory`, :class:`~factory.RelatedFactory`),
the parent's strategy will be pushed onto related factories.
Calling a :class:`~factory.Factory` subclass will provide an object through the default strategy:
.. code-block:: python
class MyFactory(factory.Factory):
class Meta:
model = MyClass
.. code-block:: pycon
>>> MyFactory.create()
<MyFactory: X (saved)>
>>> MyFactory.build()
<MyFactory: X (unsaved)>
>>> MyFactory() # equivalent to MyFactory.create()
<MyClass: X (saved)>
The default strategy can be changed by setting the ``class Meta`` :attr:`~factory.FactoryOptions.strategy` attribute.
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