feat: add NeverNone to always generate an optional field

Author: iloveitaly

polyfactory/__init__.py

@@ -1,6 +1,6 @@
 from .exceptions import ConfigurationException
 from .factories import BaseFactory
-from .fields import Fixture, Ignore, PostGenerated, Require, Use
+from .fields import Fixture, Ignore, PostGenerated, Require, Use, NeverNone
 from .persistence import AsyncPersistenceProtocol, SyncPersistenceProtocol
 
 __all__ = (
@@ -11,6 +11,7 @@
     "Ignore",
     "PostGenerated",
     "Require",
+    "NeverNone",
     "SyncPersistenceProtocol",
     "Use",
 )

polyfactory/factories/base.py

@@ -54,7 +54,7 @@
 )
 from polyfactory.exceptions import ConfigurationException, MissingBuildKwargException, ParameterException
 from polyfactory.field_meta import Null
-from polyfactory.fields import Fixture, Ignore, PostGenerated, Require, Use
+from polyfactory.fields import Fixture, Ignore, NeverNone, PostGenerated, Require, Use
 from polyfactory.utils.helpers import (
     flatten_annotation,
     get_collection_type,
@@ -334,6 +334,7 @@ def _handle_factory_field(  # noqa: PLR0911
         if isinstance(field_value, Fixture):
             return field_value.to_value()
 
+        # if a raw lambda is passed, invoke it
         if callable(field_value):
             return field_value()
 
@@ -946,8 +947,12 @@ def should_set_none_value(cls, field_meta: FieldMeta) -> bool:
         :returns: A boolean determining whether 'None' should be set for the given field_meta.
 
         """
+        field_value = hasattr(cls, field_meta.name) and getattr(cls, field_meta.name)
+        never_none = field_value and isinstance(field_value, NeverNone)
+
         return (
             cls.__allow_none_optionals__
+            and not never_none
             and is_optional(field_meta.annotation)
             and create_random_boolean(random=cls.__random__)
         )
@@ -1021,13 +1026,15 @@ def _check_declared_fields_exist_in_model(cls) -> None:
                 f"{field_name} is declared on the factory {cls.__name__}"
                 f" but it is not part of the model {cls.__model__.__name__}"
             )
-            if isinstance(field_value, (Use, PostGenerated, Ignore, Require)):
+            if isinstance(field_value, (Use, PostGenerated, Ignore, Require, NeverNone)):
                 raise ConfigurationException(error_message)
 
     @classmethod
     def process_kwargs(cls, **kwargs: Any) -> dict[str, Any]:
         """Process the given kwargs and generate values for the factory's model.
 
+        If you need to deeply customize field values, you'll want to override this method.
+
         :param kwargs: Any build kwargs.
 
         :returns: A dictionary of build results.
@@ -1038,8 +1045,11 @@ def process_kwargs(cls, **kwargs: Any) -> dict[str, Any]:
         for field_meta in cls.get_model_fields():
             field_build_parameters = cls.extract_field_build_parameters(field_meta=field_meta, build_args=kwargs)
             if cls.should_set_field_value(field_meta, **kwargs) and not cls.should_use_default_value(field_meta):
-                if hasattr(cls, field_meta.name) and not hasattr(BaseFactory, field_meta.name):
-                    field_value = getattr(cls, field_meta.name)
+                field_value = getattr(cls, field_meta.name, None)
+
+                # TODO why do we need the BaseFactory check here, only dunder methods which are ignored would trigger this?
+                # NeverNone should be treated as a normally-generated field
+                if field_value and not hasattr(BaseFactory, field_meta.name) and not isinstance(field_value, NeverNone):
                     if isinstance(field_value, Ignore):
                         continue
 

polyfactory/fields.py

@@ -22,6 +22,10 @@ class Require:
     """A factory field that marks an attribute as a required build-time kwarg."""
 
 
+class NeverNone:
+    """A factory field that marks as always generated, even if it's an optional"""
+
+
 class Ignore:
     """A factory field that marks an attribute as ignored."""