Fix alias resolution for default settings source. (#468)

Co-authored-by: Hasan Ramezani <[email protected]>

Author: kschwab

pydantic_settings/sources.py

@@ -39,7 +39,6 @@
 from dotenv import dotenv_values
 from pydantic import AliasChoices, AliasPath, BaseModel, Json, RootModel, TypeAdapter
 from pydantic._internal._repr import Representation
-from pydantic._internal._signature import _field_name_for_signature
 from pydantic._internal._typing_extra import WithArgsTypes, origin_is_union, typing_base
 from pydantic._internal._utils import deep_update, is_model_class, lenient_issubclass
 from pydantic.dataclasses import is_pydantic_dataclass
@@ -336,10 +335,12 @@ def __init__(self, settings_cls: type[BaseSettings], nested_model_default_partia
         )
         if self.nested_model_default_partial_update:
             for field_name, field_info in settings_cls.model_fields.items():
+                alias_names, *_ = _get_alias_names(field_name, field_info)
+                preferred_alias = alias_names[0]
                 if is_dataclass(type(field_info.default)):
-                    self.defaults[_field_name_for_signature(field_name, field_info)] = asdict(field_info.default)
+                    self.defaults[preferred_alias] = asdict(field_info.default)
                 elif is_model_class(type(field_info.default)):
-                    self.defaults[_field_name_for_signature(field_name, field_info)] = field_info.default.model_dump()
+                    self.defaults[preferred_alias] = field_info.default.model_dump()
 
     def get_field_value(self, field: FieldInfo, field_name: str) -> tuple[Any, str, bool]:
         # Nothing to do here. Only implement the return statement to make mypy happy
@@ -1422,41 +1423,6 @@ def _get_sub_models(self, model: type[BaseModel], field_name: str, field_info: F
                 sub_models.append(type_)  # type: ignore
         return sub_models
 
-    def _get_alias_names(
-        self, field_name: str, field_info: FieldInfo, alias_path_args: dict[str, str]
-    ) -> tuple[tuple[str, ...], bool]:
-        alias_names: list[str] = []
-        is_alias_path_only: bool = True
-        if not any((field_info.alias, field_info.validation_alias)):
-            alias_names += [field_name]
-            is_alias_path_only = False
-        else:
-            new_alias_paths: list[AliasPath] = []
-            for alias in (field_info.alias, field_info.validation_alias):
-                if alias is None:
-                    continue
-                elif isinstance(alias, str):
-                    alias_names.append(alias)
-                    is_alias_path_only = False
-                elif isinstance(alias, AliasChoices):
-                    for name in alias.choices:
-                        if isinstance(name, str):
-                            alias_names.append(name)
-                            is_alias_path_only = False
-                        else:
-                            new_alias_paths.append(name)
-                else:
-                    new_alias_paths.append(alias)
-            for alias_path in new_alias_paths:
-                name = cast(str, alias_path.path[0])
-                name = name.lower() if not self.case_sensitive else name
-                alias_path_args[name] = 'dict' if len(alias_path.path) > 2 else 'list'
-                if not alias_names and is_alias_path_only:
-                    alias_names.append(name)
-        if not self.case_sensitive:
-            alias_names = [alias_name.lower() for alias_name in alias_names]
-        return tuple(dict.fromkeys(alias_names)), is_alias_path_only
-
     def _verify_cli_flag_annotations(self, model: type[BaseModel], field_name: str, field_info: FieldInfo) -> None:
         if _CliImplicitFlag in field_info.metadata:
             cli_flag_name = 'CliImplicitFlag'
@@ -1481,7 +1447,7 @@ def _sort_arg_fields(self, model: type[BaseModel]) -> list[tuple[str, FieldInfo]
                 if not field_info.is_required():
                     raise SettingsError(f'subcommand argument {model.__name__}.{field_name} has a default value')
                 else:
-                    alias_names, *_ = self._get_alias_names(field_name, field_info, {})
+                    alias_names, *_ = _get_alias_names(field_name, field_info)
                     if len(alias_names) > 1:
                         raise SettingsError(f'subcommand argument {model.__name__}.{field_name} has multiple aliases')
                     field_types = [type_ for type_ in get_args(field_info.annotation) if type_ is not type(None)]
@@ -1495,7 +1461,7 @@ def _sort_arg_fields(self, model: type[BaseModel]) -> list[tuple[str, FieldInfo]
                 if not field_info.is_required():
                     raise SettingsError(f'positional argument {model.__name__}.{field_name} has a default value')
                 else:
-                    alias_names, *_ = self._get_alias_names(field_name, field_info, {})
+                    alias_names, *_ = _get_alias_names(field_name, field_info)
                     if len(alias_names) > 1:
                         raise SettingsError(f'positional argument {model.__name__}.{field_name} has multiple aliases')
                 positional_args.append((field_name, field_info))
@@ -1597,7 +1563,9 @@ def _add_parser_args(
         alias_path_args: dict[str, str] = {}
         for field_name, field_info in self._sort_arg_fields(model):
             sub_models: list[type[BaseModel]] = self._get_sub_models(model, field_name, field_info)
-            alias_names, is_alias_path_only = self._get_alias_names(field_name, field_info, alias_path_args)
+            alias_names, is_alias_path_only = _get_alias_names(
+                field_name, field_info, alias_path_args=alias_path_args, case_sensitive=self.case_sensitive
+            )
             preferred_alias = alias_names[0]
             if _CliSubCommand in field_info.metadata:
                 for model in sub_models:
@@ -2241,5 +2209,41 @@ def _get_model_fields(model_cls: type[Any]) -> dict[str, FieldInfo]:
     raise SettingsError(f'Error: {model_cls.__name__} is not subclass of BaseModel or pydantic.dataclasses.dataclass')
 
 
+def _get_alias_names(
+    field_name: str, field_info: FieldInfo, alias_path_args: dict[str, str] = {}, case_sensitive: bool = True
+) -> tuple[tuple[str, ...], bool]:
+    alias_names: list[str] = []
+    is_alias_path_only: bool = True
+    if not any((field_info.alias, field_info.validation_alias)):
+        alias_names += [field_name]
+        is_alias_path_only = False
+    else:
+        new_alias_paths: list[AliasPath] = []
+        for alias in (field_info.alias, field_info.validation_alias):
+            if alias is None:
+                continue
+            elif isinstance(alias, str):
+                alias_names.append(alias)
+                is_alias_path_only = False
+            elif isinstance(alias, AliasChoices):
+                for name in alias.choices:
+                    if isinstance(name, str):
+                        alias_names.append(name)
+                        is_alias_path_only = False
+                    else:
+                        new_alias_paths.append(name)
+            else:
+                new_alias_paths.append(alias)
+        for alias_path in new_alias_paths:
+            name = cast(str, alias_path.path[0])
+            name = name.lower() if not case_sensitive else name
+            alias_path_args[name] = 'dict' if len(alias_path.path) > 2 else 'list'
+            if not alias_names and is_alias_path_only:
+                alias_names.append(name)
+    if not case_sensitive:
+        alias_names = [alias_name.lower() for alias_name in alias_names]
+    return tuple(dict.fromkeys(alias_names)), is_alias_path_only
+
+
 def _is_function(obj: Any) -> bool:
     return isinstance(obj, (FunctionType, BuiltinFunctionType))

tests/test_settings.py

@@ -13,6 +13,7 @@
 from annotated_types import MinLen
 from pydantic import (
     AliasChoices,
+    AliasGenerator,
     AliasPath,
     BaseModel,
     Discriminator,
@@ -621,6 +622,26 @@ def settings_customise_sources(
     assert s.model_dump() == s_final
 
 
+def test_alias_nested_model_default_partial_update():
+    class SubModel(BaseModel):
+        v1: str = 'default'
+        v2: bytes = b'hello'
+        v3: int
+
+    class Settings(BaseSettings):
+        model_config = SettingsConfigDict(
+            nested_model_default_partial_update=True, alias_generator=AliasGenerator(lambda s: s.replace('_', '-'))
+        )
+
+        v0: str = 'ok'
+        sub_model: SubModel = SubModel(v1='top default', v3=33)
+
+    assert Settings(**{'sub-model': {'v1': 'cli'}}).model_dump() == {
+        'v0': 'ok',
+        'sub_model': {'v1': 'cli', 'v2': b'hello', 'v3': 33},
+    }
+
+
 def test_env_str(env):
     class Settings(BaseSettings):
         apple: str = Field(None, validation_alias='BOOM')