^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Each HTTP request runs inside an independent SQLAlchemy session (as well

as in an independent database transaction). ``Session`` is the session manager

and factory. ``Session()`` will create a new session on-demand or return the

current session for the active thread. Many database operations are methods on

Database model objects

(almost) always belong to a particular SQLAlchemy session, which means

that SQLAlchemy will ensure that they're kept in sync with the database

(but also means that they cannot be shared across requests).