Bring back Encoder/Decoder in DBSettings

Summary:
An amendment to D15335716 -- turns out we do need Encoder/Decoder in DBSettings, rather than Config, otherwise there's no easy way to make it work with Facebook.

(Keeping the url/creator change, though.)

Differential Revision: D15352973

fbshipit-source-id: 463451842fb4acf9d97322c59d8de2e4be632ad4

ax/service/utils/storage.py

@@ -2,8 +2,8 @@
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 from ax.core.experiment import Experiment
 from ax.storage.sqa_store.db import init_engine_and_session_factory
-from ax.storage.sqa_store.load import load_experiment as _load_experiment
-from ax.storage.sqa_store.save import save_experiment as _save_experiment
+from ax.storage.sqa_store.load import _load_experiment
+from ax.storage.sqa_store.save import _save_experiment
 from ax.storage.sqa_store.structs import DBSettings
 
 
@@ -22,7 +22,7 @@ def load_experiment(name: str, db_settings: DBSettings) -> Experiment:
         ax.core.Experiment: Loaded experiment.
     """
     init_engine_and_session_factory(creator=db_settings.creator, url=db_settings.url)
-    experiment = _load_experiment(name, db_settings.config)
+    experiment = _load_experiment(name, decoder=db_settings.decoder)
     if not isinstance(experiment, Experiment) or experiment.is_simple_experiment:
         raise ValueError("Service API only supports Experiment")
     return experiment
@@ -37,4 +37,4 @@ def save_experiment(experiment: Experiment, db_settings: DBSettings) -> None:
         db_settings: Defines behavior for loading/saving experiment to/from db.
     """
     init_engine_and_session_factory(creator=db_settings.creator, url=db_settings.url)
-    _save_experiment(experiment, db_settings.config)
+    _save_experiment(experiment, encoder=db_settings.encoder)

ax/storage/sqa_store/structs.py

@@ -3,14 +3,18 @@
 
 from typing import Callable, NamedTuple, Optional
 
+from ax.storage.sqa_store.decoder import Decoder
+from ax.storage.sqa_store.encoder import Encoder
 from ax.storage.sqa_store.sqa_config import SQAConfig
 
 
 class DBSettings(NamedTuple):
     """
     Defines behavior for loading/saving experiment to/from db.
+    Either creator or url must be specified as a way to connect to the SQL db.
     """
 
-    config: Optional[SQAConfig] = SQAConfig()
     creator: Optional[Callable] = None
+    decoder: Decoder = Decoder(config=SQAConfig())
+    encoder: Encoder = Encoder(config=SQAConfig())
     url: Optional[str] = None