Automatically define factory boy recipes for dataclasses by inspecting the type annotations

autofactory.py

## See https://github.com/FactoryBoy/factory_boy/issues/836
import inspect
from typing import List, get_args, get_origin
import factory
import factory.fuzzy
from dataclasses import dataclass, Field, MISSING, is_dataclass
from enum import Enum
from datetime import date, datetime
from decimal import Decimal


def get_auto_field(field: Field):
    if field.default is not MISSING:
        return field.default

    elif field.type is str and 'email' in field.name:
        return factory.Faker("ascii_email")

    elif field.type is datetime:
        return factory.Faker("date_time_between")
    elif field.type is date:
        return factory.Faker("date_object")

    elif is_dataclass(field.type):
        # fixme reflect the factory un a better way than eval
        return factory.SubFactory(eval(f"{field.type.__name__}AutoFactory"))

    elif inspect.isclass(field.type) and issubclass(field.type, Enum):
        return factory.fuzzy.FuzzyChoice(field.type.__members__.values())

    elif get_origin(field.type) in [list, tuple, set]:
        args = get_args(field.type)

        return factory.Faker(f"py{get_origin(field.type).__name__}", value_types=args)

    # str, int, float, decimal
    return factory.Faker(f"py{field.type.__name__.lower()}")



def auto_factory(target_model, field_overrides=None):

    factory_name = f'{target_model.__name__}AutoFactory'
    class Meta:
        model = target_model

    attrs = {name: get_auto_field(field) for name, field in target_model.__dataclass_fields__.items()}

    attrs.update(field_overrides or {})

    attrs['Meta'] = Meta

    factory_class = type(factory_name, (factory.Factory,), attrs)
    return factory_class



@dataclass
class A:
    a_text: str
    integer: int
    email: str
    value: float
    a_date: date
    d: Decimal = Decimal("42")


class MyEnum(Enum):
    option1 = 1
    option2 = 2


@dataclass
class B:
    related: A
    an_enum: MyEnum
    list_of_str: List[str]


AAutoFactory = auto_factory(A)
BAutoFactory = auto_factory(B)



"""
In [84]: b = BAutoFactory()

In [85]: b
Out[85]: B(related=A(a_text='sAywZloMAosFzdiYWTfd', integer=1118, email='[email protected]', value=-1487703326176.12, a_date=datetime.date(1979, 3, 8), d=Decimal('42')), an_enum=<MyEnum.option2: 2>, list_of_str=['JpDECtFLEmVTSzdHsIdV', 'HPAoyVmnStBoAtaSFvuE', 'AsTaUioIxLMxSqFaWPRt', 'uiRCFswCMwtbLTfjiaBK', 'sySmxSnkLhlxPJdyGWAa', 'ZwYWLZYswgXpSjNxLUOs', 'UjStmZkSMnVdgYBApUrx', 'ONryhrSHgrIVECmAOzuQ', 'LGmBZVOyXrKWnJbXkMNB', 'UGADWrTORVOKIqJGwPOG'])

In [86]: b.related
Out[86]: A(a_text='sAywZloMAosFzdiYWTfd', integer=1118, email='[email protected]', value=-1487703326176.12, a_date=datetime.date(1979, 3, 8), d=Decimal('42'))

In [87]: b.an_enum
Out[87]: <MyEnum.option2: 2>

In [88]: b2 = BAutoFactory()

In [89]: b2.an_enum
Out[89]: <MyEnum.option2: 2>

In [90]: b2 = BAutoFactory()

In [91]: b2.an_enum
Out[91]: <MyEnum.option1: 1>

In [92]: b.list_of_str
Out[92]:
['JpDECtFLEmVTSzdHsIdV',
 'HPAoyVmnStBoAtaSFvuE',
 'AsTaUioIxLMxSqFaWPRt',
 'uiRCFswCMwtbLTfjiaBK',
 'sySmxSnkLhlxPJdyGWAa',
 'ZwYWLZYswgXpSjNxLUOs',
 'UjStmZkSMnVdgYBApUrx',
 'ONryhrSHgrIVECmAOzuQ',
 'LGmBZVOyXrKWnJbXkMNB',
 'UGADWrTORVOKIqJGwPOG']
"""

@SHxKM looks like https://pypi.org/project/typing-extensions/ backports those functions