feat(core): AWEL flow 2.0 backend code (#1879)

Co-authored-by: yhjun1026 <460342015@qq.com>

dbgpt/serve/flow/serve.py

@@ -4,6 +4,7 @@ from typing import List, Optional, Union
 from sqlalchemy import URL
 
 from dbgpt.component import SystemApp
+from dbgpt.core.interface.variables import VariablesProvider
 from dbgpt.serve.core import BaseServe
 from dbgpt.storage.metadata import DatabaseManager
 
@@ -40,6 +41,8 @@ class Serve(BaseServe):
             system_app, api_prefix, api_tags, db_url_or_db, try_create_tables
         )
         self._db_manager: Optional[DatabaseManager] = None
+        self._variables_provider: Optional[VariablesProvider] = None
+        self._serve_config: Optional[ServeConfig] = None
 
     def init_app(self, system_app: SystemApp):
         if self._app_has_initiated:
@@ -62,5 +65,37 @@ class Serve(BaseServe):
 
     def before_start(self):
         """Called before the start of the application."""
-        # TODO: Your code here
+        from dbgpt.core.interface.variables import (
+            FernetEncryption,
+            StorageVariablesProvider,
+        )
+        from dbgpt.storage.metadata.db_storage import SQLAlchemyStorage
+        from dbgpt.util.serialization.json_serialization import JsonSerializer
+
+        from .models.models import ServeEntity, VariablesEntity
+        from .models.variables_adapter import VariablesAdapter
+
         self._db_manager = self.create_or_get_db_manager()
+        self._serve_config = ServeConfig.from_app_config(
+            self._system_app.config, SERVE_CONFIG_KEY_PREFIX
+        )
+
+        self._db_manager = self.create_or_get_db_manager()
+        storage_adapter = VariablesAdapter()
+        serializer = JsonSerializer()
+        storage = SQLAlchemyStorage(
+            self._db_manager,
+            VariablesEntity,
+            storage_adapter,
+            serializer,
+        )
+        self._variables_provider = StorageVariablesProvider(
+            storage=storage,
+            encryption=FernetEncryption(self._serve_config.encrypt_key),
+            system_app=self._system_app,
+        )
+
+    @property
+    def variables_provider(self):
+        """Get the variables provider of the serve app with db storage"""
+        return self._variables_provider