Fixes #452 - Adding support for populate_by_name and some tests to validate this works.

Author: hozn

pydantic_settings/sources.py

@@ -445,10 +445,12 @@ def _extract_field_info(self, field: FieldInfo, field_name: str) -> list[tuple[s
                         )
             else:  # string validation alias
                 field_info.append((v_alias, self._apply_case_sensitive(v_alias), False))
-        elif origin_is_union(get_origin(field.annotation)) and _union_is_complex(field.annotation, field.metadata):
-            field_info.append((field_name, self._apply_case_sensitive(self.env_prefix + field_name), True))
-        else:
-            field_info.append((field_name, self._apply_case_sensitive(self.env_prefix + field_name), False))
+
+        if not v_alias or self.config.get('populate_by_name', False):
+            if origin_is_union(get_origin(field.annotation)) and _union_is_complex(field.annotation, field.metadata):
+                field_info.append((field_name, self._apply_case_sensitive(self.env_prefix + field_name), True))
+            else:
+                field_info.append((field_name, self._apply_case_sensitive(self.env_prefix + field_name), False))
 
         return field_info
 

tests/test_settings.py

@@ -64,6 +64,12 @@ class SettingWithIgnoreEmpty(BaseSettings):
     model_config = SettingsConfigDict(env_ignore_empty=True)
 
 
+class SettingWithPopulateByName(BaseSettings):
+    apple: str = Field('default', alias='pomo')
+
+    model_config = SettingsConfigDict(populate_by_name=True)
+
+
 def test_sub_env(env):
     env.set('apple', 'hello')
     s = SimpleSettings()
@@ -127,6 +133,110 @@ class Settings(BaseSettings):
     assert s.a == 'b'
 
 
+def test_populate_by_name_when_using_alias(env):
+    env.set('pomo', 'bongusta')
+    s = SettingWithPopulateByName()
+    assert s.apple == 'bongusta'
+
+
+def test_populate_by_name_when_using_name(env):
+    env.set('apple', 'honeycrisp')
+    s = SettingWithPopulateByName()
+    assert s.apple == 'honeycrisp'
+
+
+def test_populate_by_name_when_using_both(env):
+    env.set('apple', 'honeycrisp')
+    env.set('pomo', 'bongusta')
+    s = SettingWithPopulateByName()
+    assert s.apple == 'bongusta', 'Expected alias value to be prioritized.'
+
+
+def test_populate_by_name_with_alias_path_when_using_alias(env):
+    env.set('fruits', '["empire", "honeycrisp"]')
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', validation_alias=AliasPath('fruits', 0))
+        model_config = SettingsConfigDict(populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == 'empire'
+
+
+def test_populate_by_name_with_alias_path_when_using_name(env):
+    env.set('apple', 'jonathan gold')
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', validation_alias=AliasPath('fruits', 0))
+        model_config = SettingsConfigDict(populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == 'jonathan gold'
+
+
+@pytest.mark.parametrize(
+    'env_vars, expected_value',
+    [
+        pytest.param({'pomo': 'pomo-chosen'}, 'pomo-chosen', id='pomo'),
+        pytest.param({'pomme': 'pomme-chosen'}, 'pomme-chosen', id='pomme'),
+        pytest.param({'manzano': 'manzano-chosen'}, 'manzano-chosen', id='manzano'),
+        pytest.param(
+            {'pomo': 'pomo-chosen', 'pomme': 'pomme-chosen', 'manzano': 'manzano-chosen'},
+            'pomo-chosen',
+            id='pomo-priority',
+        ),
+        pytest.param({'pomme': 'pomme-chosen', 'manzano': 'manzano-chosen'}, 'pomme-chosen', id='pomme-priority'),
+    ],
+)
+def test_populate_by_name_with_alias_choices_when_using_alias(env, env_vars: dict[str, str], expected_value: str):
+    for k, v in env_vars.items():
+        env.set(k, v)
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', validation_alias=AliasChoices('pomo', 'pomme', 'manzano'))
+        model_config = SettingsConfigDict(populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == expected_value
+
+
+def test_populate_by_name_with_dotenv_when_using_alias(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('pomo=bongusta')
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', alias='pomo')
+        model_config = SettingsConfigDict(env_file=p, populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == 'bongusta'
+
+
+def test_populate_by_name_with_dotenv_when_using_name(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('apple=honeycrisp')
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', alias='pomo')
+        model_config = SettingsConfigDict(env_file=p, populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == 'honeycrisp'
+
+
+def test_populate_by_name_with_dotenv_when_using_both(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('apple=honeycrisp')
+    p.write_text('pomo=bongusta')
+
+    class Settings(BaseSettings):
+        apple: str = Field('default', alias='pomo')
+        model_config = SettingsConfigDict(env_file=p, populate_by_name=True)
+
+    s = Settings()
+    assert s.apple == 'bongusta', 'Expected alias value to be prioritized.'
+
+
 def test_with_prefix(env):
     class Settings(BaseSettings):
         apple: str