Refactor Sessions to clarify their usage

DBSession has been renamed to HandlerSession.

The following exist now:
- HandlerSession: a DB session scoped to the current handler;
  should therefore only be used inside handlers.
- ThreadSession: a DB session scoped to the current thread;
  should be used outside of handlers, e.g. when firing off
  tasks in threads, or inside of services.

A special HandlerSession, with knowledge of the current user, and that
verifies permissions on commit, is available as `self.Session` on the
base handler. This is the *preferred way of accessing* HandlerSession.

To make it easier to get hold of the current engine, the Sessions each
have a `.engine` attribute: `HandlerSession.engine`.

This avoids having to access the engine as
`HandlerSession.session_factory.kw["bind"]`.

.pre-commit-config.yaml

@@ -23,7 +23,7 @@ repos:
         pass_filenames: true
         exclude: baselayer|node_modules|static
   - repo: https://github.com/pycqa/flake8
-    rev: 3.8.4
+    rev: 6.1.0
     hooks:
       - id: flake8
         pass_filenames: true

app/access.py

@@ -5,7 +5,7 @@
 from sqlalchemy.orm import joinedload
 
 from baselayer.app.custom_exceptions import AccessError  # noqa: F401
-from baselayer.app.models import DBSession, Role, Token, User  # noqa: F401
+from baselayer.app.models import HandlerSession, Role, Token, User  # noqa: F401
 
 
 def auth_or_token(method):
@@ -26,7 +26,7 @@ def wrapper(self, *args, **kwargs):
         token_header = self.request.headers.get("Authorization", None)
         if token_header is not None and token_header.startswith("token "):
             token_id = token_header.replace("token", "").strip()
-            with DBSession() as session:
+            with HandlerSession() as session:
                 token = session.scalars(
                     sa.select(Token)
                     .options(

app/handlers/base.py

@@ -22,7 +22,13 @@
 from ..env import load_env
 from ..flow import Flow
 from ..json_util import to_json
-from ..models import DBSession, User, VerifiedSession, bulk_verify, session_context_id
+from ..models import (
+    HandlerSession,
+    User,
+    VerifiedSession,
+    bulk_verify,
+    session_context_id,
+)
 
 env, cfg = load_env()
 log = make_log("basehandler")
@@ -49,7 +55,7 @@ def get_current_user(self):
         user_id = int(self.user_id())
         oauth_uid = self.get_secure_cookie("user_oauth_uid")
         if user_id and oauth_uid:
-            with DBSession() as session:
+            with HandlerSession() as session:
                 try:
                     user = session.scalars(
                         sqlalchemy.select(User).where(User.id == user_id)
@@ -74,7 +80,7 @@ def get_current_user(self):
             return None
 
     def login_user(self, user):
-        with DBSession() as session:
+        with HandlerSession() as session:
             try:
                 self.set_secure_cookie("user_id", str(user.id))
                 user = session.scalars(
@@ -120,7 +126,7 @@ def log_exception(self, typ=None, value=None, tb=None):
             )
 
     def on_finish(self):
-        DBSession.remove()
+        HandlerSession.remove()
 
 
 class BaseHandler(PSABaseHandler):
@@ -153,7 +159,7 @@ def Session(self):
             # must merge the user object with the current session
             # ref: https://docs.sqlalchemy.org/en/14/orm/session_basics.html#adding-new-or-existing-items
             session.add(self.current_user)
-            session.bind = DBSession.session_factory.kw["bind"]
+            session.bind = HandlerSession.engine
             yield session
 
     def verify_permissions(self):
@@ -164,20 +170,20 @@ def verify_permissions(self):
         """
 
         # get items to be inserted
-        new_rows = [row for row in DBSession().new]
+        new_rows = [row for row in HandlerSession().new]
 
         # get items to be updated
         updated_rows = [
-            row for row in DBSession().dirty if DBSession().is_modified(row)
+            row for row in HandlerSession().dirty if HandlerSession().is_modified(row)
         ]
 
         # get items to be deleted
-        deleted_rows = [row for row in DBSession().deleted]
+        deleted_rows = [row for row in HandlerSession().deleted]
 
         # get items that were read
         read_rows = [
             row
-            for row in set(DBSession().identity_map.values())
+            for row in set(HandlerSession().identity_map.values())
             - (set(updated_rows) | set(new_rows) | set(deleted_rows))
         ]
 
@@ -194,15 +200,15 @@ def verify_permissions(self):
         # update transaction state in DB, but don't commit yet. this updates
         # or adds rows in the database and uses their new state in joins,
         # for permissions checking purposes.
-        DBSession().flush()
+        HandlerSession().flush()
         bulk_verify("create", new_rows, self.current_user)
 
     def verify_and_commit(self):
         """Verify permissions on the current database session and commit if
         successful, otherwise raise an AccessError.
         """
         self.verify_permissions()
-        DBSession().commit()
+        HandlerSession().commit()
 
     def prepare(self):
         self.cfg = self.application.cfg
@@ -225,7 +231,7 @@ def prepare(self):
         N = 5
         for i in range(1, N + 1):
             try:
-                assert DBSession.session_factory.kw["bind"] is not None
+                assert HandlerSession.engine is not None
             except Exception as e:
                 if i == N:
                     raise e

app/model_util.py

@@ -21,15 +21,15 @@ def status(message):
     else:
         print(f"\r[✓] {message}")
     finally:
-        models.DBSession().commit()
+        models.HandlerSession().commit()
 
 
 def drop_tables():
-    conn = models.DBSession.session_factory.kw["bind"]
-    print(f"Dropping tables on database {conn.url.database}")
+    engine = models.HandlerSession.engine
+    print(f"Dropping tables on database {engine.url.database}")
     meta = sa.MetaData()
-    meta.reflect(bind=conn)
-    meta.drop_all(bind=conn)
+    meta.reflect(bind=engine)
+    meta.drop_all(bind=engine)
 
 
 def create_tables(retry=5, add=True):
@@ -45,17 +45,16 @@ def create_tables(retry=5, add=True):
         tables.
 
     """
-    conn = models.DBSession.session_factory.kw["bind"]
     tables = models.Base.metadata.sorted_tables
     if tables and not add:
         print("Existing tables found; not creating additional tables")
         return
 
     for i in range(1, retry + 1):
         try:
-            conn = models.DBSession.session_factory.kw["bind"]
-            print(f"Creating tables on database {conn.url.database}")
-            models.Base.metadata.create_all(conn)
+            engine = models.HandlerSession.engine
+            print(f"Creating tables on database {engine.url.database}")
+            models.Base.metadata.create_all(engine)
 
             table_list = ", ".join(list(models.Base.metadata.tables.keys()))
             print(f"Refreshed tables: {table_list}")