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Auto-activate for polyfactory, ModelFactory, DataclassFactory, MsgspecFactory, AttrsFactory, Use, register_fixture, pytest plugin, __random_seed__, or coverage(). Not for production seeding.
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| name | polyfactory |
| description | Auto-activate for polyfactory, ModelFactory, DataclassFactory, MsgspecFactory, AttrsFactory, Use, register_fixture, pytest plugin, __random_seed__, or coverage(). Not for production seeding. |
Polyfactory is a typed mock-data factory library: declare ModelFactory[T] (or DataclassFactory, MsgspecFactory, AttrsFactory, TypedDictFactory) and .build() returns a populated instance of T. The matching factory base inspects the model's annotations and supported constraints so tests do not need hand-written happy-path fixtures.
In Litestar projects, polyfactory's pytest plugin is the canonical way to feed TestClient.post(...) / AsyncTestClient.put(...) payloads. The companion skill litestar:litestar-testing covers the request side.
T | None, never Optional[T].ModelFactory (Pydantic), DataclassFactory, MsgspecFactory, AttrsFactory, TypedDictFactory. A mismatched base raises ConfigurationException.register_fixture over hand-rolled @pytest.fixture wrappers. Call it in a pytest-discovered test module or conftest.py so the injected fixture is collected.| Model kind | Factory base | Import |
|---|---|---|
pydantic.BaseModel | ModelFactory | from polyfactory.factories.pydantic_factory import ModelFactory |
@dataclass | DataclassFactory | from polyfactory.factories import DataclassFactory |
msgspec.Struct | MsgspecFactory | from polyfactory.factories.msgspec_factory import MsgspecFactory |
@attrs.define / attr.s | AttrsFactory | from polyfactory.factories.attrs_factory import AttrsFactory |
TypedDict | TypedDictFactory | from polyfactory.factories.typed_dict_factory import TypedDictFactory |
| Beanie / Odmantic / SQLA | dedicated bases | see factories.md |
from dataclasses import dataclass
from polyfactory.factories import DataclassFactory
@dataclass
class Order:
id: int
customer_email: str
total_cents: int
status: str
class OrderFactory(DataclassFactory[Order]):
pass
# Use it
one = OrderFactory.build()
many = OrderFactory.batch(10)
The single concrete generic argument lets Polyfactory infer __model__. build() returns one instance, batch(n) returns list[T], and coverage() yields the smallest set of instances that covers the model's supported variants.
from polyfactory import Use
from polyfactory.factories import DataclassFactory
class OrderFactory(DataclassFactory[Order]):
# Plain literal — every build returns this exact value
status = "pending"
# Callable — re-evaluated per build
customer_email = Use(lambda: "test@example.com")
# Random choice — re-evaluated per build
total_cents = Use(DataclassFactory.__random__.randint, 100, 10_000)
Use(callable, *args, **kwargs) is re-invoked on every build(), so each generated instance gets a fresh value.
Use PostGenerated when a field depends on values generated for the same instance:
from typing import Any
from polyfactory import PostGenerated
def order_reference(name: str, values: dict[str, Any], prefix: str) -> str:
return f"{prefix}-{values['id']}"
class OrderFactory(DataclassFactory[Order]):
reference = PostGenerated(order_reference, "order")
The callback signature is (field_name, generated_values, *args, **kwargs). generated_values contains the non-post-generated fields.
class OrderFactory(DataclassFactory[Order]):
__random_seed__ = 42 # same seed → same output across runs
Set __random_seed__ (or __faker__ = Faker(seed=...) for finer Faker control) when test assertions depend on the exact generated values.
class CustomerFactory(DataclassFactory[Customer]):
__set_as_default_factory_for_type__ = True
@dataclass
class Order:
id: int
customer: Customer # automatically populated by CustomerFactory.build()
class OrderFactory(DataclassFactory[Order]):
pass
When __set_as_default_factory_for_type__ = True, polyfactory uses that factory whenever the type appears as a field on another model — no manual nesting required.
from polyfactory.pytest_plugin import register_fixture
from polyfactory.factories import DataclassFactory
@register_fixture
class OrderFactory(DataclassFactory[Order]):
pass
def test_order_total(order_factory: type[OrderFactory]) -> None:
order = order_factory.build()
assert order.total_cents >= 0
@register_fixture returns the class unchanged and injects a pytest fixture into the caller's module. The fixture name is the snake-cased class name and its value is the factory class.
from polyfactory import Use
from polyfactory.pytest_plugin import register_fixture
@register_fixture
class CustomerFactory(DataclassFactory[Customer]):
__set_as_default_factory_for_type__ = True
@register_fixture
class OrderFactory(DataclassFactory[Order]):
customer = Use(CustomerFactory.build) # explicit local override
__set_as_default_factory_for_type__ = True lets Polyfactory populate nested Customer fields with CustomerFactory. Use Use(CustomerFactory.build) when one parent factory needs an explicit local override.
Match the base to your model backend (table above). A mismatched base fails during factory class creation. If your project uses multiple backends (e.g., Pydantic for HTTP DTOs + msgspec for internal events), import each base separately and don't try to share a factory across backends.
Subclass the appropriate base with one concrete generic argument and let Polyfactory infer __model__. Set __model__ explicitly only when the generic declaration cannot identify exactly one model. Keep factories in tests/factories.py or tests/<feature>/factories.py, outside production code paths.
If a field can take any valid value, leave it for the factory to randomize. Override (literal value or Use(...)) only fields the assertion depends on. Tests that pin every field defeat the purpose of using a factory.
For factories used in many tests, decorate with @register_fixture in a pytest-discovered module and consume the snake-cased fixture name. For one-off use, call Factory.build() directly inline.
Set __set_as_default_factory_for_type__ = True on a base factory and let nested fields be populated automatically, or use Use(OtherFactory.build) for a local relationship override.
Tests that assert on specific generated values need __random_seed__. Tests that assert on shape or invariants (e.g., total >= 0) should not — leaving randomization on widens coverage across runs.
__model__. Polyfactory infers __model__ from DataclassFactory[Order]; an unparameterized concrete factory without __model__ raises ConfigurationException during class creation.status = "pending") or assert on shape, not both.__random_seed__ across factories that share a Faker instance. They will collide and produce unexpected duplicates. Use a different seed per factory or a single shared seeded __faker__.ModelFactory on a msgspec.Struct raises ConfigurationException; use MsgspecFactory.tests/. Importing them from production modules ties test data to runtime code and is a refactor hazard.coverage() is not a Cartesian-product generator. It emits a minimal representative set and reuses exhausted field variants; use Hypothesis for exhaustive input-space exploration.__allow_none_optionals__ is boolean. True allows random None values during build(); False always generates the wrapped type. It is not a probability.create_async() and create_batch_async() require __async_persistence__ or a backend factory that supplies it. Polyfactory has no build_async().Before delivering polyfactory code, verify:
ModelFactory, dataclass → DataclassFactory, msgspec → MsgspecFactory, attrs → AttrsFactory).__model__.tests/ (or a sibling test-only module), never in production code.__random_seed__ is set; otherwise it is not.@register_fixture is used for factories shared across more than ~2 test files; one-offs call .build() inline.__set_as_default_factory_for_type__ or Use(OtherFactory.build).register_fixture is invoked in a pytest-discovered module.create_async() / create_batch_async() only when persistence is configured.# tests/factories.py
from polyfactory.factories.msgspec_factory import MsgspecFactory
from myapp.events import OrderCreatedEvent # msgspec.Struct
class OrderCreatedEventFactory(MsgspecFactory[OrderCreatedEvent]):
pass
# tests/conftest.py
from polyfactory.pytest_plugin import register_fixture
from tests.factories import OrderCreatedEventFactory
register_fixture(OrderCreatedEventFactory)
# tests/test_orders.py
from __future__ import annotations # consumer module — fine to use future annotations
import msgspec
import pytest
from litestar.testing import AsyncTestClient
from tests.factories import OrderCreatedEventFactory
@pytest.mark.anyio
async def test_create_order_emits_event(
client: AsyncTestClient,
order_created_event_factory: type[OrderCreatedEventFactory],
) -> None:
payload = order_created_event_factory.build()
response = await client.post("/orders", json=msgspec.to_builtins(payload))
assert response.status_code == 201
assert response.json()["id"] == payload.id
The factory provides a fully-populated, validation-passing OrderCreatedEvent; the test focuses on the request/response contract instead of constructing fake data inline.
For detailed guides, refer to the following documents in references/:
PostGenerated, model coverage, persistence protocols, and SQLAlchemy 3.3 persistence behavior.@register_fixture, separate registration from conftest.py, fixture scoping and naming, collection boundaries, and async persistence.TestClient / AsyncTestClient, parametrizing handler tests via coverage(), integrating with litestar-testing fixtures, msgspec DTOs, advanced-alchemy model factories, and SAQ task payload generation.