Fix a bug when we have case insentive field in nested model (#294)

Author: hramezani

pydantic_settings/sources.py

@@ -274,14 +274,24 @@ class Settings(BaseSettings):
         for name, value in field_values.items():
             sub_model_field: FieldInfo | None = None
 
+            annotation = field.annotation
+
+            # If field is Optional, we need to find the actual type
+            args = get_args(annotation)
+            if origin_is_union(get_origin(field.annotation)) and len(args) == 2 and type(None) in args:
+                for arg in args:
+                    if arg != type(None):
+                        annotation = arg
+                        break
+
             # This is here to make mypy happy
             # Item "None" of "Optional[Type[Any]]" has no attribute "model_fields"
-            if not field.annotation or not hasattr(field.annotation, 'model_fields'):
+            if not annotation or not hasattr(annotation, 'model_fields'):
                 values[name] = value
                 continue
 
             # Find field in sub model by looking in fields case insensitively
-            for sub_model_field_name, f in field.annotation.model_fields.items():
+            for sub_model_field_name, f in annotation.model_fields.items():
                 if not f.validation_alias and sub_model_field_name.lower() == name.lower():
                     sub_model_field = f
                     break
@@ -337,7 +347,7 @@ def __call__(self) -> dict[str, Any]:
                         field_value = None
                 if (
                     not self.case_sensitive
-                    and lenient_issubclass(field.annotation, BaseModel)
+                    # and lenient_issubclass(field.annotation, BaseModel)
                     and isinstance(field_value, dict)
                 ):
                     data[field_key] = self._replace_field_names_case_insensitively(field, field_value)

tests/test_settings.py

@@ -2648,3 +2648,19 @@ class Settings(BaseSettings):
     )
     s = Settings()
     assert s.model_dump() == {'nested': {'foo': 'string'}}
+
+
+def test_case_insensitive_nested_optional(env):
+    class NestedSettings(BaseModel):
+        FOO: str
+        BaR: int
+
+    class Settings(BaseSettings):
+        model_config = SettingsConfigDict(env_nested_delimiter='__', case_sensitive=False)
+
+        nested: Optional[NestedSettings]
+
+    env.set('nested__FoO', 'string')
+    env.set('nested__bar', '123')
+    s = Settings()
+    assert s.model_dump() == {'nested': {'BaR': 123, 'FOO': 'string'}}