Improve explode_env_vars for better dict handling (#261)

Author: hramezani

pydantic_settings/sources.py

@@ -604,6 +604,8 @@ def explode_env_vars(self, field_name: str, field: FieldInfo, env_vars: Mapping[
         Returns:
             A dictionary contains extracted values from nested env values.
         """
+        is_dict = lenient_issubclass(get_origin(field.annotation), dict)
+
         prefixes = [
             f'{env_name}{self.env_nested_delimiter}' for _, env_name, _ in self._extract_field_info(field, field_name)
         ]
@@ -624,11 +626,15 @@ def explode_env_vars(self, field_name: str, field: FieldInfo, env_vars: Mapping[
             target_field = self.next_field(target_field, last_key)
 
             # check if env_val maps to a complex field and if so, parse the env_val
-            if target_field and env_val:
-                is_complex, allow_json_failure = self._field_is_complex(target_field)
+            if (target_field or is_dict) and env_val:
+                if target_field:
+                    is_complex, allow_json_failure = self._field_is_complex(target_field)
+                else:
+                    # nested field type is dict
+                    is_complex, allow_json_failure = True, False
                 if is_complex:
                     try:
-                        env_val = self.decode_complex_value(last_key, target_field, env_val)
+                        env_val = self.decode_complex_value(last_key, target_field, env_val)  # type: ignore
                     except ValueError as e:
                         if not allow_json_failure:
                             raise e

tests/test_settings.py

@@ -2348,3 +2348,19 @@ class Settings(BaseSettings):
 
     s = Settings(nested_foo=NestedSettings(fooAlias='EXAMPLE'))
     assert s.model_dump() == {'nested_foo': {'foo': 'EXAMPLE'}}
+
+
+def test_nested_models_as_dict_value(env):
+    class NestedSettings(BaseModel):
+        foo: Dict[str, int]
+
+    class Settings(BaseSettings):
+        nested: NestedSettings
+        sub_dict: Dict[str, NestedSettings]
+
+        model_config = SettingsConfigDict(env_nested_delimiter='__')
+
+    env.set('nested__foo', '{"a": 1}')
+    env.set('sub_dict__bar__foo', '{"b": 2}')
+    s = Settings()
+    assert s.model_dump() == {'nested': {'foo': {'a': 1}}, 'sub_dict': {'bar': {'foo': {'b': 2}}}}