Using factory_boy with ORMs

factory_boy provides custom Factory subclasses for various ORMs, adding dedicated features.

Django

The first versions of factory_boy were designed specifically for Django, but the library has now evolved to be framework-independent.

Most features should thus feel quite familiar to Django users.

The `DjangoModelFactory` subclass

All factories for a Django Model should use the DjangoModelFactory base class.

class factory.django.DjangoModelFactory(factory.Factory)[source]

Dedicated class for Django Model factories.

This class provides the following features:

The model attribute also supports the 'app.Model' syntax
create() uses Model.objects.create()
When using RelatedFactory or PostGeneration attributes, the base object will be saved once all post-generation hooks have run.

Note

With Django versions 1.8.0 to 1.8.3, it was no longer possible to call .build() on a factory if this factory used a SubFactory pointing to another model: Django refused to set a ForeignKey to an unsaved Model instance.

See https://code.djangoproject.com/ticket/10811 and https://code.djangoproject.com/ticket/25160 for details.

class factory.django.DjangoOptions(factory.base.FactoryOptions)[source]

The class Meta on a DjangoModelFactory supports extra parameters:

database: New in version 2.5.0.

All queries to the related model will be routed to the given database. It defaults to 'default'.

django_get_or_create

New in version 2.4.0.

Fields whose name are passed in this list will be used to perform a Model.objects.get_or_create() instead of the usual Model.objects.create():

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = 'myapp.User'  # Equivalent to ``model = myapp.models.User``
        django_get_or_create = ('username',)

    username = 'john'

>>> User.objects.all()
[]
>>> UserFactory()                   # Creates a new user
<User: john>
>>> User.objects.all()
[<User: john>]

>>> UserFactory()                   # Fetches the existing user
<User: john>
>>> User.objects.all()              # No new user!
[<User: john>]

>>> UserFactory(username='jack')    # Creates another user
<User: jack>
>>> User.objects.all()
[<User: john>, <User: jack>]

Extra fields

class factory.django.FileField[source]

Custom declarations for django.db.models.FileField

__init__(self, from_path='', from_file='', data=b'', filename='example.dat')[source]

Parameters

from_path (str) – Use data from the file located at from_path, and keep its filename
from_file (file) – Use the contents of the provided file object; use its filename if available, unless filename is also provided.
from_func (func) – Use function that returns a file object
data (bytes) – Use the provided bytes as file contents
filename (str) – The filename for the FileField

Note

If the value None was passed for the FileField field, this will disable field generation:

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

    the_file = factory.django.FileField(filename='the_file.dat')

>>> MyFactory(the_file__data=b'uhuh').the_file.read()
b'uhuh'
>>> MyFactory(the_file=None).the_file
None

class factory.django.ImageField[source]

Custom declarations for django.db.models.ImageField

__init__(self, from_path='', from_file='', filename='example.jpg', width=100, height=100, color='green', format='JPEG')

Parameters

from_path (str) – Use data from the file located at from_path, and keep its filename
from_file (file) – Use the contents of the provided file object; use its filename if available
from_func (func) – Use function that returns a file object
filename (str) – The filename for the ImageField
width (int) – The width of the generated image (default: 100)
height (int) – The height of the generated image (default: 100)
color (str) – The color of the generated image (default: 'green')
format (str) – The image format (as supported by PIL) (default: 'JPEG')

Note

If the value None was passed for the FileField field, this will disable field generation:

Note

Just as Django’s django.db.models.ImageField requires the Python Imaging Library, this ImageField requires it too.

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

    the_image = factory.django.ImageField(color='blue')

>>> MyFactory(the_image__width=42).the_image.width
42
>>> MyFactory(the_image=None).the_image
None

Disabling signals

Signals are often used to plug some custom code into external components code; for instance to create Profile objects on-the-fly when a new User object is saved.

This may interfere with finely tuned factories, which would create both using RelatedFactory.

To work around this problem, use the mute_signals() decorator/context manager:

factory.django.mute_signals(signal1, ...)[source]: Disable the list of selected signals when calling the factory, and reactivate them upon leaving.

# foo/factories.py

import factory
import factory.django

from . import models
from . import signals

@factory.django.mute_signals(signals.pre_save, signals.post_save)
class FooFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = models.Foo

    # ...

def make_chain():
    with factory.django.mute_signals(signals.pre_save, signals.post_save):
        # pre_save/post_save won't be called here.
        return SomeFactory(), SomeOtherFactory()

Mogo

factory_boy supports Mogo-style models, through the MogoFactory class.

Mogo is a wrapper around the pymongo library for MongoDB.

class factory.mogo.MogoFactory(factory.Factory)[source]

Dedicated class for Mogo models.

This class provides the following features:

build() calls a model’s new() method
create() builds an instance through new() then saves it.

MongoEngine

factory_boy supports MongoEngine-style models, through the MongoEngineFactory class.

mongoengine is a wrapper around the pymongo library for MongoDB.

class factory.mongoengine.MongoEngineFactory(factory.Factory)[source]

Dedicated class for MongoEngine models.

This class provides the following features:

build() calls a model’s __init__ method
create() builds an instance through __init__ then saves it.

Note

If the associated class <factory.FactoryOptions.model is a mongoengine.EmbeddedDocument, the create() function won’t “save” it, since this wouldn’t make sense.

This feature makes it possible to use SubFactory to create embedded document.

A minimalist example:

import mongoengine

class Address(mongoengine.EmbeddedDocument):
    street = mongoengine.StringField()

class Person(mongoengine.Document):
    name = mongoengine.StringField()
    address = mongoengine.EmbeddedDocumentField(Address)

import factory

class AddressFactory(factory.mongoengine.MongoEngineFactory):
    class Meta:
        model = Address

    street = factory.Sequence(lambda n: 'street%d' % n)

class PersonFactory(factory.mongoengine.MongoEngineFactory):
    class Meta:
        model = Person

    name = factory.Sequence(lambda n: 'name%d' % n)
    address = factory.SubFactory(AddressFactory)

SQLAlchemy

Factoy_boy also supports SQLAlchemy models through the SQLAlchemyModelFactory class.

To work, this class needs an SQLAlchemy session object affected to the Meta.sqlalchemy_session attribute.

class factory.alchemy.SQLAlchemyModelFactory(factory.Factory)[source]

Dedicated class for SQLAlchemy models.

This class provides the following features:

create() uses sqlalchemy.orm.session.Session.add()

class factory.alchemy.SQLAlchemyOptions(factory.base.FactoryOptions)[source]

In addition to the usual parameters available in class Meta, a SQLAlchemyModelFactory also supports the following settings:

sqlalchemy_session: SQLAlchemy session to use to communicate with the database when creating an object through this SQLAlchemyModelFactory.

sqlalchemy_session_persistence

Control the action taken by sqlalchemy session at the end of a create call.

Valid values are:

None: do nothing
'flush': perform a session flush()
'commit': perform a session commit()

The default value is None.

If force_flush is set to True, it overrides this option.

force_flush: Force a session flush() at the end of _create().

Note

This option is deprecated. Use sqlalchemy_session_persistence instead.

A (very) simple example:

from sqlalchemy import Column, Integer, Unicode, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker

engine = create_engine('sqlite://')
session = scoped_session(sessionmaker(bind=engine))
Base = declarative_base()


class User(Base):
    """ A SQLAlchemy simple model class who represents a user """
    __tablename__ = 'UserTable'

    id = Column(Integer(), primary_key=True)
    name = Column(Unicode(20))

Base.metadata.create_all(engine)

import factory

class UserFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = User
        sqlalchemy_session = session   # the SQLAlchemy session object

    id = factory.Sequence(lambda n: n)
    name = factory.Sequence(lambda n: u'User %d' % n)

>>> session.query(User).all()
[]
>>> UserFactory()
<User: User 1>
>>> session.query(User).all()
[<User: User 1>]

Managing sessions

Since SQLAlchemy is a general purpose library, there is no “global” session management system.

The most common pattern when working with unit tests and factory_boy is to use SQLAlchemy’s sqlalchemy.orm.scoping.scoped_session:

The test runner configures some project-wide scoped_session
Each SQLAlchemyModelFactory subclass uses this scoped_session as its sqlalchemy_session
The tearDown() method of tests calls Session.remove to reset the session.

Note

See the excellent SQLAlchemy guide on scoped_session for details of scoped_session’s usage.

The basic idea is that declarative parts of the code (including factories) need a simple way to access the “current session”, but that session will only be created and configured at a later point.

The scoped_session handles this, by virtue of only creating the session when a query is sent to the database.

Here is an example layout:

A global (test-only?) file holds the scoped_session:

# myprojet/test/common.py

from sqlalchemy import orm
Session = orm.scoped_session(orm.sessionmaker())

All factory access it:

# myproject/factories.py

import factory
import factory.alchemy

from . import models
from .test import common

class UserFactory(factory.alchemy.SQLAlchemyModelFactory):
    class Meta:
        model = models.User

        # Use the not-so-global scoped_session
        # Warning: DO NOT USE common.Session()!
        sqlalchemy_session = common.Session

    name = factory.Sequence(lambda n: "User %d" % n)

The test runner configures the scoped_session when it starts:

# myproject/test/runtests.py

import sqlalchemy

from . import common

def runtests():
    engine = sqlalchemy.create_engine('sqlite://')

    # It's a scoped_session, and now is the time to configure it.
    common.Session.configure(bind=engine)

    run_the_tests

test cases use this scoped_session, and clear it after each test (for isolation):

# myproject/test/test_stuff.py

import unittest

from . import common

class MyTest(unittest.TestCase):

    def setUp(self):
        # Prepare a new, clean session
        self.session = common.Session()

    def test_something(self):
        u = factories.UserFactory()
        self.assertEqual([u], self.session.query(User).all())

    def tearDown(self):
        # Rollback the session => no changes to the database
        self.session.rollback()
        # Remove it, so that the next test gets a new Session()
        common.Session.remove()

Using factory_boy with ORMs

Django

The DjangoModelFactory subclass

Extra fields

Disabling signals

Mogo

MongoEngine

SQLAlchemy

Managing sessions

The `DjangoModelFactory` subclass