Delay Sqlalchemy import in DB trigger

Since Sqlalchemy is only used server-side, it's an extraneous
dependency of the SDK-only install

covalent/triggers/database_trigger.py

@@ -19,9 +19,6 @@
 from threading import Event
 from typing import List
 
-from sqlalchemy import create_engine
-from sqlalchemy.orm import Session
-
 from covalent._shared_files import logger
 
 from .base import BaseTrigger
@@ -88,6 +85,12 @@ def observe(self) -> None:
         where conditions are met or until stop has being called
         """
 
+        # Since these modules are only used server-side, delay their
+        # imports to avoid introducing a sqlalchemy requirement to
+        # SDK-only installs
+        from sqlalchemy import create_engine
+        from sqlalchemy.orm import Session
+
         app_log.debug("Inside DatabaseTrigger's observe")
         event_count = 0
 

tests/covalent_tests/triggers/database_trigger_test.py

@@ -61,8 +61,8 @@ def test_database_trigger_observe(mocker, where_clauses, database_trigger):
     database_trigger.where_clauses = where_clauses
     database_trigger.trigger = mocker.MagicMock()
 
-    mock_db_engine = mocker.patch("covalent.triggers.database_trigger.create_engine")
-    mock_session = mocker.patch("covalent.triggers.database_trigger.Session")
+    mock_db_engine = mocker.patch("sqlalchemy.create_engine")
+    mock_session = mocker.patch("sqlalchemy.orm.Session")
     mock_event = mocker.patch("covalent.triggers.database_trigger.Event")
     mock_sleep = mocker.patch("covalent.triggers.database_trigger.time.sleep")