Support for async?

[remarkov]

The problem

Coming from Django where we used Factory Boy really a lot to a new, async stack to fully support GraphQL with subscriptions which are really cool (uvicorn + Starlette + Ariadne) we also switched to async ORM (not really an ORM) named GINO. It is based on SQLAlchemy Core and works pretty robust. However, I am struggling to adapt Factory Boy to use GINO models.

Proposed solution

At first glance I thought that I need to implement _create() method in my factory model but the problem is that the create() method for GINO model is a coroutine and can't be called from a synchronous code. I tried to experiment with asyncio._get_running_loop() but I am really new to async stuff and my attempt failed.

Extra notes

I am using pytest with pytest-asyncio plugin to run tests with async code which works pretty well including working with DB. For that I have this in my conftest.py:

@pytest.fixture(scope="session")
def event_loop():
    """
    This is to make the asyncio event loop shared for the whole test session, otherwise
    it will be recreated for each test which will prevent using the test_db fixture.
    """
    loop = asyncio.get_event_loop()
    yield loop
    loop.close()

@pytest.fixture(autouse=True, scope="session")
async def test_db(request):
    """
    Here is some DB preparation code like (re)creating DB itself, making sure we have all 
    necessary rights etc.
    """
    await db.gino.create_all()  # this is to bind the GINO engine to DB

    yield  # passing context back to the tests

    await db.pop_bind().close()  # unbinding engine and performing other teardown later

I really miss Factory Boy and hope there is an easy solution to start my factories again. I also created an issue for GINO here https://github.com/fantix/gino/issues/608 but decided to open one here too as I think Factory Boy developed a much wider community and I have better chances that someone has the same problem as I do. Thanks all!

[remarkov]

Sometimes you just need to lay down your thoughts to get the proper idea. Also, the fresh mind helps (I was doing my experiments at 4am yesterday:)

I am not sure this is correct way to proceed and whether there are some unforeseen consequences that will shot me in the knee later but here's what I did:

import uuid

import factory

from database import models

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

    nickname = factory.Sequence(lambda n: f"Test User {n}")
    uuid = factory.LazyAttribute(lambda _: str(uuid.uuid4()))

    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        async def create_coro(*args, **kwargs):
            return await model_class.create(*args, **kwargs)

        return create_coro(*args, **kwargs)

Then in my test I do

new_user = await UserFactory()

and get my new shiny user object created properly in DB! So far I am very happy with the result.

If more wise and experienced developers won't see any issues with this approach I think it may worse adding something like this to the recipes section as async stack is getting more and more popular. I am leaving this issue open for now as I hope there will be some comments and/or advice. If not, it is absolutely fine to close it.

[PSzczepanski1996]

Hey, do you know how I can maybe define awaitable Mock in your code? I need to define abstract without ORM factory like that:

class ObjectFactory(factory.Factory):

    class Meta:
        abstract = True
        model = Mock

    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        async def create_coro(*args, **kwargs):
            return await model_class(*args, **kwargs)

        return create_coro(*args, **kwargs)

But mock is not awaitable. I'm trying to figure that out.

[graingert]

https://mock.readthedocs.io/en/latest/changelog.html#b1 has AsyncMock

[nadege]

Thanks, that really helped me. I extended your version to support more features.

class AsyncFactory(factory.Factory):
    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        async def maker_coroutine():
            for key, value in kwargs.items():
        # when using SubFactory, you'll have a Task in the corresponding kwarg
        # await tasks to pass model instances instead
                if inspect.isawaitable(value):
                    kwargs[key] = await value
        # replace as needed by your way of creating model instances
            return await model_class.create_async(*args, **kwargs)

    # A Task can be awaited multiple times, unlike a coroutine.
    # useful when a factory and a subfactory must share a same object
        return asyncio.create_task(maker_coroutine())

    @classmethod
    async def create_batch(cls, size, **kwargs):
        return [await cls.create(**kwargs) for _ in range(size)]

class UserFactory(AsyncFactory):
    ...

class Category(AsyncFactory):
   ...
   creator = factory.SubFactory(UserFactory)

class ArticleFactory(AsyncFactory):
   ...
   author = factory.SubFactory(UserFactory)
   category = factory.SubFactory(CategoryFactory, creator=factory.SelfAttribute(..author))

In the following example:

article = await ArticleFactory.create()
assert article.author == article.category.creator

The _create function of UserFactory is called to create the Article Author, this returns a Task. Then the _create_ function of Category is called, with the User creation Task in its kwarg, which is awaited. The category model creation can use the User instance. Finally the _create function of Article is called, also with the User creation Task. It is awaited again. The user instance is used in the article creation.

[mdczaplicki]

Here comes my solution to this.
It allows to provide a custom coroutine for saving the object in the database. It also allows to update the object before returning, so that you can still have an id generated on the server side.

Partially inspired by @nadege :smile:

class AsyncFactoryOptions(factory.base.FactoryOptions):
    def _build_default_options(self):
        def is_coroutine(meta, value):
            if not inspect.iscoroutinefunction(value):
                raise TypeError(f"{repr(value)} is not a coroutine, but {type(value)}")

        return super()._build_default_options() + [
            factory.base.OptionDefault("save_coroutine", None, inherit=True, checker=is_coroutine)
        ]

class AsyncFactory(factory.Factory):
    _options_class = AsyncFactoryOptions

    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        """
        This method saves the object using asynchronous save function.
        If the coroutine returns a value, it's expected to be the same type as it's parameter.
        This logic is made so that eg. id can be generated on the database side.
        """
        return asyncio.get_event_loop().run_until_complete(cls._create_async(model_class, *args, **kwargs))

    @classmethod
    async def _create_async(cls, model_class, *args, **kwargs):
        for key, value in kwargs.items():
            # when using SubFactory, you'll have a Task in the corresponding kwarg
            # await tasks to pass model instances instead
            if inspect.isawaitable(value):
                kwargs[key] = await value

        obj = model_class(*args, **kwargs)
        updated_obj = await cls._meta.save_coroutine(obj)
        if updated_obj is None:
            return obj
        if not isinstance(updated_obj, model_class):
            raise TypeError(
                f"Object returned from the save_coroutine has different type than factory's model. "
                f"Expected: {model_class}, Got: {type(updated_obj)}"
            )
        return updated_obj

Usage:

class MountainFactory(AsyncFactory):
    class Meta:
        model = Mountain
        save_coroutine = save_mountain

[KharchenkoDmitriy]

I also tried to use factory boy with an async ORM and tried to use RelatedFactory. At that point just returning a task in not enough, so I've tried to replace a StepBuilder in _generate method

I got this:

import inspect
import factory
from factory.builder import StepBuilder, BuildStep, parse_declarations

class AsyncFactory(factory.Factory):
    @classmethod
    async def _generate(cls, strategy, params):
        if cls._meta.abstract:
            raise factory.errors.FactoryError(
                "Cannot generate instances of abstract factory %(f)s; "
                "Ensure %(f)s.Meta.model is set and %(f)s.Meta.abstract "
                "is either not set or False." % dict(f=cls.__name__))

        step = AsyncStepBuilder(cls._meta, params, strategy)
        return await step.build()

    @classmethod
    async def _create(cls, model_class, *args, **kwargs):
        for key, value in kwargs.items():
            if inspect.isawaitable(value):
                kwargs[key] = await value
        return await model_class.create(*args, **kwargs)

    @classmethod
    async def create_batch(cls, size, **kwargs):
        return [await cls.create(**kwargs) for _ in range(size)]

class AsyncStepBuilder(StepBuilder):
    # Redefine build function that await for instance creation and awaitable postgenerations
    async def build(self, parent_step=None, force_sequence=None):
        """Build a factory instance."""
        # TODO: Handle "batch build" natively
        pre, post = parse_declarations(
            self.extras,
            base_pre=self.factory_meta.pre_declarations,
            base_post=self.factory_meta.post_declarations,
        )

        if force_sequence is not None:
            sequence = force_sequence
        elif self.force_init_sequence is not None:
            sequence = self.force_init_sequence
        else:
            sequence = self.factory_meta.next_sequence()

        step = BuildStep(
            builder=self,
            sequence=sequence,
            parent_step=parent_step,
        )
        step.resolve(pre)

        args, kwargs = self.factory_meta.prepare_arguments(step.attributes)

        instance = await self.factory_meta.instantiate(
            step=step,
            args=args,
            kwargs=kwargs,
        )

        postgen_results = {}
        for declaration_name in post.sorted():
            declaration = post[declaration_name]
            declaration_result = declaration.declaration.evaluate_post(
                instance=instance,
                step=step,
                overrides=declaration.context,
            )
            if inspect.isawaitable(declaration_result):
                    declaration_result = await declaration_result
            postgen_results[declaration_name] = declaration_result

        self.factory_meta.use_postgeneration_results(
            instance=instance,
            step=step,
            results=postgen_results,
        )
        return instance

I'm trying to avoid using asyncio.create_task as I want to control the order in which models instantiated. So I've directly awaited factory_meta.instantiate method and after awaited all awaitable post-generations

[B3QL]

Another version that works with async SQLAlchemy:

import factory
from factory.alchemy import SESSION_PERSISTENCE_COMMIT, SESSION_PERSISTENCE_FLUSH
from factory.builder import StepBuilder, BuildStep, parse_declarations

class AsyncFactory(factory.alchemy.SQLAlchemyModelFactory):
    @classmethod
    async def _generate(cls, strategy, params):
        if cls._meta.abstract:
            raise factory.errors.FactoryError(
                "Cannot generate instances of abstract factory %(f)s; "
                "Ensure %(f)s.Meta.model is set and %(f)s.Meta.abstract "
                "is either not set or False." % dict(f=cls.__name__))

        step = AsyncStepBuilder(cls._meta, params, strategy)
        return await step.build()

    @classmethod
    async def _create(cls, model_class, *args, **kwargs):
        for key, value in kwargs.items():
            if inspect.isawaitable(value):
                kwargs[key] = await value
        return await super()._create(model_class, *args, **kwargs)

    @classmethod
    async def create_batch(cls, size, **kwargs):
        return [await cls.create(**kwargs) for _ in range(size)]

    @classmethod
    async def _save(cls, model_class, session, args, kwargs):
        session_persistence = cls._meta.sqlalchemy_session_persistence
        obj = model_class(*args, **kwargs)
        session.add(obj)
        if session_persistence == SESSION_PERSISTENCE_FLUSH:
            await session.flush()
        elif session_persistence == SESSION_PERSISTENCE_COMMIT:
            await session.commit()
        return obj

class AsyncStepBuilder(StepBuilder):
    # Redefine build function that await for instance creation and awaitable postgenerations
    async def build(self, parent_step=None, force_sequence=None):
        """Build a factory instance."""
        # TODO: Handle "batch build" natively
        pre, post = parse_declarations(
            self.extras,
            base_pre=self.factory_meta.pre_declarations,
            base_post=self.factory_meta.post_declarations,
        )

        if force_sequence is not None:
            sequence = force_sequence
        elif self.force_init_sequence is not None:
            sequence = self.force_init_sequence
        else:
            sequence = self.factory_meta.next_sequence()

        step = BuildStep(
            builder=self,
            sequence=sequence,
            parent_step=parent_step,
        )
        step.resolve(pre)

        args, kwargs = self.factory_meta.prepare_arguments(step.attributes)

        instance = await self.factory_meta.instantiate(
            step=step,
            args=args,
            kwargs=kwargs,
        )

        postgen_results = {}
        for declaration_name in post.sorted():
            declaration = post[declaration_name]
            declaration_result = declaration.declaration.evaluate_post(
                instance=instance,
                step=step,
                overrides=declaration.context,
            )
            if inspect.isawaitable(declaration_result):
                    declaration_result = await declaration_result
            postgen_results[declaration_name] = declaration_result

        self.factory_meta.use_postgeneration_results(
            instance=instance,
            step=step,
            results=postgen_results,
        )
        return instance

[Andrew-Chen-Wang]

Coming from a Django background and with the async Django ORM added, def willing to add a PR for async capability + Django async capability. The examples above create a new class, which is preferable in most libraries, but I think in this case: creating an "a" prefix method would work best in case someone wants to use both sync and async methods but reuse the declarations.

[Andrew-Chen-Wang]

If anyone needs a Django version. Note this utilizes Django 4.2's new addition of "asave", but it'll take account for it if you are on a lower version.

https://gist.github.com/Andrew-Chen-Wang/59d784496c63ee65714b926d6945b4c6

Factory implementation:

import inspect

import factory
from asgiref.sync import sync_to_async
from django.db import IntegrityError
from factory import errors
from factory.builder import BuildStep, StepBuilder, parse_declarations

def use_postgeneration_results(self, step, instance, results):
    return self.factory._after_postgeneration(
        instance,
        create=step.builder.strategy == factory.enums.CREATE_STRATEGY,
        results=results,
    )

factory.base.FactoryOptions.use_postgeneration_results = use_postgeneration_results

class AsyncFactory(factory.django.DjangoModelFactory):
    @classmethod
    async def _generate(cls, strategy, params):
        if cls._meta.abstract:
            raise factory.errors.FactoryError(
                "Cannot generate instances of abstract factory %(f)s; "
                "Ensure %(f)s.Meta.model is set and %(f)s.Meta.abstract "
                "is either not set or False." % dict(f=cls.__name__)
            )

        step = AsyncStepBuilder(cls._meta, params, strategy)
        return await step.build()

    class Meta:
        abstract = True  # Optional, but explicit.

    @classmethod
    async def _get_or_create(cls, model_class, *args, **kwargs):
        """Create an instance of the model through objects.get_or_create."""
        manager = cls._get_manager(model_class)

        assert "defaults" not in cls._meta.django_get_or_create, (
            "'defaults' is a reserved keyword for get_or_create "
            "(in %s._meta.django_get_or_create=%r)"
            % (cls, cls._meta.django_get_or_create)
        )

        key_fields = {}
        for field in cls._meta.django_get_or_create:
            if field not in kwargs:
                raise errors.FactoryError(
                    "django_get_or_create - "
                    "Unable to find initialization value for '%s' in factory %s"
                    % (field, cls.__name__)
                )
            key_fields[field] = kwargs.pop(field)
        key_fields["defaults"] = kwargs

        try:
            instance, _created = await manager.aget_or_create(*args, **key_fields)
        except IntegrityError as e:
            get_or_create_params = {
                lookup: value
                for lookup, value in cls._original_params.items()
                if lookup in cls._meta.django_get_or_create
            }
            if get_or_create_params:
                try:
                    instance = await manager.aget(**get_or_create_params)
                except manager.model.DoesNotExist:
                    # Original params are not a valid lookup and triggered a create(),
                    # that resulted in an IntegrityError. Follow Django’s behavior.
                    raise e
            else:
                raise e

        return instance

    @classmethod
    async def _create(cls, model_class, *args, **kwargs):
        """Create an instance of the model, and save it to the database."""
        if cls._meta.django_get_or_create:
            return await cls._get_or_create(model_class, *args, **kwargs)

        manager = cls._get_manager(model_class)
        return await manager.acreate(*args, **kwargs)

    @classmethod
    async def create_batch(cls, size, **kwargs):
        """Create a batch of instances of the model, and save them to the database."""
        return [await cls.create(**kwargs) for _ in range(size)]

    @classmethod
    async def _after_postgeneration(cls, instance, create, results=None):
        """Save again the instance if creating and at least one hook ran."""
        if create and results:
            # Some post-generation hooks ran, and may have modified us.
            if hasattr(instance, "asave"):
                await instance.asave()
            else:
                await sync_to_async(instance.save)()

class AsyncBuildStep(BuildStep):
    async def resolve(self, declarations):
        self.stub = factory.builder.Resolver(
            declarations=declarations,
            step=self,
            sequence=self.sequence,
        )

        for field_name in declarations:
            attr = getattr(self.stub, field_name)
            if inspect.isawaitable(attr):
                attr = await attr
            self.attributes[field_name] = attr

class AsyncStepBuilder(StepBuilder):
    # Redefine build function that await for instance creation and awaitable postgenerations
    async def build(self, parent_step=None, force_sequence=None):
        """Build a factory instance."""
        # TODO: Handle "batch build" natively
        pre, post = parse_declarations(
            self.extras,
            base_pre=self.factory_meta.pre_declarations,
            base_post=self.factory_meta.post_declarations,
        )

        if force_sequence is not None:
            sequence = force_sequence
        elif self.force_init_sequence is not None:
            sequence = self.force_init_sequence
        else:
            sequence = self.factory_meta.next_sequence()

        step = AsyncBuildStep(
            builder=self,
            sequence=sequence,
            parent_step=parent_step,
        )
        await step.resolve(pre)

        args, kwargs = self.factory_meta.prepare_arguments(step.attributes)

        instance = self.factory_meta.instantiate(
            step=step,
            args=args,
            kwargs=kwargs,
        )
        if inspect.isawaitable(instance):
            instance = await instance

        postgen_results = {}
        for declaration_name in post.sorted():
            declaration = post[declaration_name]
            declaration_result = declaration.declaration.evaluate_post(
                instance=instance,
                step=step,
                overrides=declaration.context,
            )
            if inspect.isawaitable(declaration_result):
                declaration_result = await declaration_result
            postgen_results[declaration_name] = declaration_result

        postgen = self.factory_meta.use_postgeneration_results(
            instance=instance,
            step=step,
            results=postgen_results,
        )
        if inspect.isawaitable(postgen):
            await postgen
        return instance

[rarestg]

@B3QL How do you recommend using your AsyncFactory implementation? I feel like I'm doing something wrong here.

I've defined a Person as such:

class PersonFactory(AsyncFactory):
    class Meta:
        model = Person

    id = factory.Faker("uuid4")
    first_name = factory.Faker("first_name")
    last_name = factory.Faker("last_name")
    dob = factory.Faker("date_of_birth", minimum_age=18, maximum_age=90)
    gender = factory.Faker("random_element", elements=("Male", "Female"))

I'm using pytest, my models are defined with SQLAlchemy 2, and my DB connections are async. Here's the fixture I'm using to get my DB sessions during tests:

@pytest.fixture
async def dbsession(
    _engine: AsyncEngine,
) -> AsyncGenerator[AsyncSession, None]:
    connection = await _engine.connect()
    trans = await connection.begin()

    session_maker = async_sessionmaker(
        connection,
        expire_on_commit=False,
    )
    session = session_maker()

    try:
        yield session
    finally:
        await session.close()
        await trans.rollback()
        await connection.close()

Now, if I try to use PersonFactory like the typical Faker use case:

@pytest.mark.anyio
async def test_videomeeting_creation(
    fastapi_app: FastAPI,
    client: AsyncClient,
    dbsession: AsyncSession,
) -> None:
    person_factory = PersonFactory()
    person = await person_factory.create()
    ...

I hit this error, since sqlalchemy_session isn't defined under Meta:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../async_factories.py:20: in _generate
    return await step.build()
../async_factories.py:72: in build
    instance = await self.factory_meta.instantiate(
../async_factories.py:27: in _create
    return await super()._create(model_class, *args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

cls = <class 'vienna.tests.factories.PatientFactory'>
model_class = <class 'vienna.db.models.patient_model.Person'>, args = ()
kwargs = {'dob': datetime.date(1994, 4, 26), 'first_name': 'Christine', 'gender': 'Female', 'id': '7ad191ee-9e3e-484b-af25-d267b5ab2870', ...}
session_factory = None, session = None

    @classmethod
    def _create(cls, model_class, *args, **kwargs):
        """Create an instance of the model, and save it to the database."""
        session_factory = cls._meta.sqlalchemy_session_factory
        if session_factory:
            cls._meta.sqlalchemy_session = session_factory()

        session = cls._meta.sqlalchemy_session

        if session is None:
>           raise RuntimeError("No session provided.")
E           RuntimeError: No session provided.

My temporary solution is a class construction function that allows me to pass my session from inside my tests:

def get_person_factory(dbsession: AsyncSession):
    class PersonFactory(AsyncFactory):
        class Meta:
            model = Person
            sqlalchemy_session = dbsession

        id = factory.Faker("uuid4")
        first_name = factory.Faker("first_name")
        last_name = factory.Faker("last_name")
        dob = factory.Faker("date_of_birth", minimum_age=18, maximum_age=90)
        gender = factory.Faker("random_element", elements=("Male", "Female"))

    return PersonFactory

But I can't help but feel this is not how you intended it to be used...

[SyntaxRules-avant]

I found this python package that implements some of the suggestions in this thread: https://github.com/kuzxnia/async_factory_boy/

[foobarfighter]

Is official async support planned for this project?

[danihodovic]

Async + Django testing (pytest) is a mess. We moved away from it altogether.

[wombat-artem]

Are you going to add async support for the SQLAlchemy? https://github.com/kuzxnia/async_factory_boy this one is pretty raw

[0xRaduan]

For anyone who comes here looking for django, I used @Andrew-Chen-Wang code here + added support for subfactory and it works perfectly:

class AsyncSubFactory(factory.SubFactory):
    async def evaluate(self, instance, step, extra):
        subfactory = self.get_factory()
        force_sequence = step.sequence if self.FORCE_SEQUENCE else None
        return await step.recurse(subfactory, extra, force_sequence=force_sequence)