Bootify webservice db session handling

solvable/src/webservice/model.py

@@ -13,18 +13,29 @@ session_factory = sessionmaker(
 )
 
 
-@contextmanager
-def Session(factory=session_factory):
-    session = factory()
-    try:
-        yield session
-        session.commit()
-    except:
-        session.rollback()
-        raise
-    # session is closed by flask
-    # finally:
-    #     session.close()
+class SessionWrapper:
+    def __init__(self):
+        self._session_factory = session_factory
+        self._session_handle = None
+
+    @contextmanager
+    def session(self):
+        try:
+            yield self._session
+            self._session.commit()
+        except:
+            self._session.rollback()
+            raise
+
+    @property
+    def _session(self):
+        if self._session_handle is None:
+            self._session_handle = self._session_factory()
+        return self._session_handle
+
+    def teardown(self):
+        if self._session_handle is not None:
+            self._session_handle.close()
 
 
 Base = declarative_base()

solvable/src/webservice/server.py

@@ -1,9 +1,8 @@
 from os import urandom, getenv
-from functools import partial
 
 from flask import Flask, render_template, request, session, url_for, g
 
-from model import init_db, session_factory, Session
+from model import init_db, SessionWrapper
 from user_ops import UserOps
 from errors import InvalidCredentialsError, UserExistsError
 
@@ -16,25 +15,24 @@ app.jinja_env.globals.update(  # pylint: disable=no-member
 )
 
 
-def get_db_session():
-    if not hasattr(g, 'db_session'):
-        g.db_session = session_factory()
-    return g.db_session
-
-Session = partial(Session, get_db_session)
+@app.before_request
+def setup_db():
+    # pylint: disable=protected-access
+    g._db_session_wrapper = SessionWrapper()
+    g.db_session = g._db_session_wrapper.session
 
 
 @app.teardown_appcontext
-def close_db_session(err): # pylint: disable=unused-argument
-    if hasattr(g, 'db_session'):
-        g.db_session.close()
+def close_db_session(_):
+    # pylint: disable=protected-access
+    g._db_session_wrapper.teardown()
 
 
 @app.route('/', methods=['GET', 'POST'])
 def index():
     if request.method == 'POST':
         try:
-            with Session() as db_session:
+            with g.db_session() as db_session:
                 UserOps(
                     request.form.get('username'),
                     request.form.get('password'),
@@ -67,7 +65,7 @@ def register():
             return render_template('register.html', alert='Passwords do not match! Please try again.')
 
         try:
-            with Session() as db_session:
+            with g.db_session() as db_session:
                 UserOps(
                     request.form.get('username'),
                     request.form.get('password'),