Fix: raise an actionable ImportError when sqlalchemy is missing, instead of a guard that does nothing

src/google/adk/sessions/__init__.py

@@ -17,7 +17,6 @@
 import importlib
 from typing import TYPE_CHECKING
 
-from ..utils._dependency import missing_extra
 from .base_session_service import BaseSessionService
 from .session import Session
 from .state import State
@@ -39,6 +38,7 @@
 ]
 
 _LAZY_MEMBERS: dict[str, str] = {
+    'DatabaseSessionService': 'database_session_service',
     'InMemorySessionService': 'in_memory_session_service',
     'VertexAiSessionService': 'vertex_ai_session_service',
 }
@@ -48,12 +48,6 @@ def __getattr__(name: str) -> object:
   if name in _LAZY_MEMBERS:
     module = importlib.import_module(f'{__name__}.{_LAZY_MEMBERS[name]}')
     return vars(module)[name]
-  if name == 'DatabaseSessionService':
-    try:
-      module = importlib.import_module(f'{__name__}.database_session_service')
-    except ImportError as e:
-      raise missing_extra('sqlalchemy', 'db') from e
-    return vars(module)['DatabaseSessionService']
   raise AttributeError(f'module {__name__!r} has no attribute {name!r}')
 
 

src/google/adk/sessions/database_session_service.py

@@ -45,8 +45,10 @@
   from sqlalchemy.ext.asyncio import AsyncSession as DatabaseSessionFactory
   from sqlalchemy.ext.asyncio import create_async_engine
   from sqlalchemy.pool import StaticPool
-except ImportError:
-  pass
+except ImportError as e:
+  from ..utils._dependency import missing_extra
+
+  raise missing_extra("sqlalchemy", "db") from e
 from typing_extensions import override
 
 from . import _session_util
@@ -316,13 +318,6 @@ def __init__(
       ValueError: If neither or both db_url and db_engine are provided, or if
         engine creation fails.
     """
-    try:
-      import sqlalchemy  # noqa: F401
-    except ImportError as e:
-      from ..utils._dependency import missing_extra
-
-      raise missing_extra("sqlalchemy", "db") from e
-
     if (db_url is None) == (db_engine is None):
       raise ValueError(
           "Exactly one of 'db_url' or 'db_engine' must be provided."

src/google/adk/sessions/migration/_schema_check_utils.py

@@ -23,8 +23,10 @@
   from sqlalchemy import inspect
   from sqlalchemy import text
   from sqlalchemy.engine import make_url
-except ImportError:
-  pass
+except ImportError as e:
+  from ...utils._dependency import missing_extra
+
+  raise missing_extra("sqlalchemy", "db") from e
 
 if TYPE_CHECKING:
   from sqlalchemy.engine import Connection

tests/unittests/test_optional_dependencies.py

@@ -126,6 +126,33 @@ def test_database_session_service_fails_on_creation():
     assert "sqlalchemy" in str(exc_info.value)
 
 
+def _import_without_sqlalchemy(module_name: str) -> None:
+  """Imports module_name in an interpreter state where sqlalchemy is missing.
+
+  ``importlib.import_module`` re-executes the module through the loader.
+  ``from <package> import <submodule>`` would instead return the stale module
+  object the parent package still holds as an attribute.
+  """
+  with mock.patch.dict("sys.modules", {"sqlalchemy": None}):
+    # Popped inside the patch so mock.patch.dict restores the entry on exit.
+    sys.modules.pop(module_name, None)
+    importlib.import_module(module_name)
+
+
+def test_database_session_service_import_reports_missing_extra():
+  """Verify importing the module without sqlalchemy names the extra."""
+  with pytest.raises(ImportError, match=r"google-adk\[db\]"):
+    _import_without_sqlalchemy("google.adk.sessions.database_session_service")
+
+
+def test_schema_check_utils_import_reports_missing_extra():
+  """Verify the schema check helper names the extra instead of half-loading."""
+  with pytest.raises(ImportError, match=r"google-adk\[db\]"):
+    _import_without_sqlalchemy(
+        "google.adk.sessions.migration._schema_check_utils"
+    )
+
+
 def test_vertex_ai_session_service_fails_on_creation():
   """Verify that creating VertexAiSessionService without extra fails using mocks."""
   try: