Storm ORM by Canonical in WSGI enabled applications (See related posts)

#!/usr/bin/env python
# vim:ts=4:sw=4:et
# (c) 2007 Vsevolod Balashov <vsevolod@balashov.name> under terms of LGPL 2.1
# use Storm ORM <https://storm.canonical.com> in WSGI enabled applications

"""WSGI middleware for Storm.

This is the database access inteface for WSGI enabled (PEP 333) web applications.

Pylons framework example:

in wsgiapp.py

from storm.database import create_database
from middlestorm import MiddleStorm
...

# CUSTOM MIDDLEWARE HERE
app = MiddleStorm(app, create_database(config['app_conf']['sqlalchemy.default.uri']))

in controller:

class DemoController(BaseController):
    def index(self):
        store = request.environ['storm.store']
        ...
"""

from storm.database import Database
from storm.store import Store
from threading import local

__all__ = ["MiddleStorm"]
__author__ = "Vsevolod Balashov <http://vsevolod.balashov.name>"
__version__ = "0.1"

class SingleConn(Database):
    """Database proxy class.
    Share single database connection between all Store object instances in threads.
    If you have readonly database or not use transactions why not?
    """
    def __init__(self, database):
        self._database = database
        self._connection = database.connect()
    def connect(self):
        return self._connection

class MiddleStorm(object):
    """WSGI middleware.
    Add Store object instance in environ['storm.store']. Each thread contains own instance.
    """

    def __init__(self, app, database, single = False):
        """Create WSGI middleware.
        @param app: up level application or middleware.
        @param database: instance of Database returned create_database.
        @param: single: use single database connection in all threads. 
        """
        assert isinstance(database, Database), \
            'database must be subclass of storm.database.Database'
        if single:
            self._database = SingleConn(database)
        else:
            self._database = database
        self._app = app
        self._local = local()

    def __call__(self, environ, start_response):
        try:
            environ['storm.store']  = self._local.store
        except AttributeError:
            environ['storm.store']  = \
                self._local.__dict__.setdefault('store', Store(self._database))
        return self._app(environ, start_response)