Metadata-Version: 1.0
Name: z3c.saconfig
Version: 0.11
Summary: Minimal SQLAlchemy ORM session configuration for Zope
Home-page: http://pypi.python.org/pypi/z3c.saconfig
Author: Martijn Faassen
Author-email: faassen@startifact.com
License: ZPL 2.1
Description: z3c.saconfig
        ************
        
        Introduction
        ============
        
        This aim of this package is to offer a simple but flexible way to
        configure SQLAlchemy's scoped session support using the Zope component
        architecture. This package is based on ``zope.sqlalchemy``, which
        offers transaction integration between Zope and SQLAlchemy.
        
        We sketch out two main scenarios here:
        
        * one database per Zope instance.
        
        * one database per site (or Grok application) in a Zope instance
        (and thus multiple databases per Zope instance).
        
        GloballyScopedSession (one database per Zope instance)
        ======================================================
        
        The simplest way to set up SQLAlchemy for Zope is to have a single
        thread-scoped session that's global to your entire Zope
        instance. Multiple applications will all share this session. The
        engine is set up with a global utility.
        
        We use the SQLAlchemy ``sqlalchemy.ext.declarative`` extension to
        define some tables and classes::
        
        >>> from sqlalchemy import *
        >>> from sqlalchemy.ext.declarative import declarative_base
        >>> from sqlalchemy.orm import relation
        
        >>> Base = declarative_base()
        >>> class User(Base):
        ...     __tablename__ = 'test_users'
        ...     id = Column('id', Integer, primary_key=True)
        ...     name = Column('name', String(50))
        ...     addresses = relation("Address", backref="user")
        >>> class Address(Base):
        ...     __tablename__ = 'test_addresses'
        ...     id = Column('id', Integer, primary_key=True)
        ...     email = Column('email', String(50))
        ...     user_id = Column('user_id', Integer, ForeignKey('test_users.id'))
        
        So far this doesn't differ from the ``zope.sqlalchemy`` example. We
        now arrive at the first difference. Instead of making the engine
        directly, we can set up the engine factory as a (global) utility. This
        utility makes sure an engine is created and cached for us.
        
        >>> from z3c.saconfig import EngineFactory
        >>> engine_factory = EngineFactory(TEST_DSN)
        
        You can pass the parameters you'd normally pass to
        ``sqlalchemy.create_engine`` to ``EngineFactory``.
        
        We now register the engine factory as a global utility using
        ``zope.component``. Normally you'd use either ZCML or Grok to do this
        confirmation, but we'll do it manually here::::
        
        >>> from zope import component
        >>> from z3c.saconfig.interfaces import IEngineFactory
        >>> component.provideUtility(engine_factory, provides=IEngineFactory)
        
        Note that setting up an engine factory is not actually necessary in
        the globally scoped use case. You could also just create the engine as
        a global and pass it as ``bind`` when you create the
        ``GloballyScopedSession`` later.
        
        Let's look up the engine by calling the factory and create the tables
        in our test database::
        
        >>> engine = engine_factory()
        >>> Base.metadata.create_all(engine)
        
        Now as for the second difference from ``zope.sqlalchemy``: how the
        session is set up and used. We'll use the ``GloballyScopedSession``
        utility to implement our session creation::
        
        >>> from z3c.saconfig import GloballyScopedSession
        
        We give the constructor to ``GloballyScopedSession`` the parameters
        you'd normally give to ``sqlalchemy.orm.create_session``, or
        ``sqlalchemy.orm.sessionmaker``::
        
        >>> utility = GloballyScopedSession(twophase=TEST_TWOPHASE)
        
        ``GlobalScopedSession`` looks up the engine using ``IEngineFactory``
        if you don't supply your own ``bind``
        argument. ``GloballyScopedSession`` also automatically sets up the
        ``autocommit``, ``autoflush`` and ``extension`` parameters to be the
        right ones for Zope integration, so normally you wouldn't need to
        supply these, but you could pass in your own if you do need it.
        
        We now register this as an ``IScopedSession`` utility::
        
        >>> from z3c.saconfig.interfaces import IScopedSession
        >>> component.provideUtility(utility, provides=IScopedSession)
        
        We are done with configuration now. As you have seen it involves
        setting up two utilities, ``IEngineFactory`` and ``IScopedSession``,
        where only the latter is really needed in this globally shared session
        use case.
        
        After the ``IScopedSession`` utility is registered, one can import the
        ``Session`` class from z3c.saconfig.  This ``Session`` class is like
        the one you'd produce with ``sessionmaker`` from
        SQLAlchemy. `z3c.saconfig.Session`` is intended to be the only
        ``Session`` class you'll ever need, as all configuration and Zope
        integration is done automatically for you by ``z3c.saconfig``,
        appropriate the context in Zope where you use it. There is no need to
        create ``Session`` classes yourself with ``sessionmaker`` or
        ``scoped_sesion`` anymore.
        
        We can now use the ``Session`` class to create a session which will
        behave according to the utility we provided::
        
        >>> from z3c.saconfig import Session
        >>> session = Session()
        
        Now things go the usual ``zope.sqlalchemy`` way, which is like
        ``SQLAlchemy`` except you can use Zope's ``transaction`` module::
        
        >>> session.query(User).all()
        []
        >>> import transaction
        >>> session.add(User(name='bob'))
        >>> transaction.commit()
        
        >>> session = Session()
        >>> bob = session.query(User).all()[0]
        >>> bob.name
        u'bob'
        >>> bob.addresses
        []
        
        Events
        ======
        
        When a new engine is created by an ``EngineFactory``, an
        ``IEngineCreatedEvent`` is fired. This event has an attribute
        ``engine`` that contains the engine that was just created::
        
        >>> from z3c.saconfig.interfaces import IEngineCreatedEvent
        >>> @component.adapter(IEngineCreatedEvent)
        ... def createdHandler(event):
        ...     print "created engine"
        >>> component.provideHandler(createdHandler)
        >>> event_engine_factory = EngineFactory(TEST_DSN1)
        >>> engine = event_engine_factory()
        created engine
        
        Let's get rid of the event handler again::
        
        >>> sm = component.getSiteManager()
        >>> sm.unregisterHandler(None,
        ...   required=[IEngineCreatedEvent])
        True
        
        SiteScopedSession (one database per site)
        =========================================
        
        In the example above we have set up SQLAlchemy with Zope using
        utilities, but it did not gain us very much, except that you can just
        use ``zope.sqlalchemy.Session`` to get the correct session.
        
        Now we'll see how we can set up different engines per site by
        registering the engine factory as a local utility for each one.
        
        In order to make this work, we'll set up ``SiteScopedSession`` instead
        of ``GloballyScopedSession``. We need to subclass
        ``SiteScopedSession`` first because we need to implement its
        ``siteScopeFunc`` method, which should return a unique ID per site
        (such as a path retrieved by ``zope.traversing.api.getPath``). We need
        to implement it here, as ``z3c.saconfig`` leaves this policy up to the
        application or a higher-level framework::
        
        >>> from z3c.saconfig import SiteScopedSession
        >>> class OurSiteScopedSession(SiteScopedSession):
        ...   def siteScopeFunc(self):
        ...      return getSite().id # the dummy site has a unique id
        >>> utility = OurSiteScopedSession()
        >>> component.provideUtility(utility, provides=IScopedSession)
        
        We want to register two engine factories, each in a different site::
        
        >>> engine_factory1 = EngineFactory(TEST_DSN1)
        >>> engine_factory2 = EngineFactory(TEST_DSN2)
        
        We need to set up the database in both new engines::
        
        >>> Base.metadata.create_all(engine_factory1())
        >>> Base.metadata.create_all(engine_factory2())
        
        Let's now create two sites, each of which will be connected to another
        engine::
        
        >>> site1 = DummySite(id=1)
        >>> site2 = DummySite(id=2)
        
        We set the local engine factories for each site:
        
        >>> sm1 = site1.getSiteManager()
        >>> sm1.registerUtility(engine_factory1, provided=IEngineFactory)
        >>> sm2 = site2.getSiteManager()
        >>> sm2.registerUtility(engine_factory2, provided=IEngineFactory)
        
        Just so we don't accidentally get it, we'll disable our global engine factory::
        
        >>> component.provideUtility(None, provides=IEngineFactory)
        
        When we set the site to ``site1``, a lookup of ``IEngineFactory`` gets
        us engine factory 1::
        
        >>> setSite(site1)
        >>> component.getUtility(IEngineFactory) is engine_factory1
        True
        
        And when we set it to ``site2``, we'll get engine factory 2::
        
        >>> setSite(site2)
        >>> component.getUtility(IEngineFactory) is engine_factory2
        True
        
        We can look up our global utility even if we're in a site::
        
        >>> component.getUtility(IScopedSession) is utility
        True
        
        Phew. That was a lot of set up, but basically this is actually just
        straightforward utility setup code; you should use the APIs or Grok's
        ``grok.local_utility`` directive to set up local utilities. Now all
        that is out of the way, we can create a session for ``site1``::
        
        >>> setSite(site1)
        >>> session = Session()
        
        The database is still empty::
        
        >>> session.query(User).all()
        []
        
        We'll add something to this database now::
        
        >>> session.add(User(name='bob'))
        >>> transaction.commit()
        
        ``bob`` is now there::
        
        >>> session = Session()
        >>> session.query(User).all()[0].name
        u'bob'
        
        Now we'll switch to ``site2``::
        
        >>> setSite(site2)
        
        If we create a new session now, we should now be working with a
        different database, which should still be empty::
        
        >>> session = Session()
        >>> session.query(User).all()
        []
        
        We'll add ``fred`` to this database::
        
        >>> session.add(User(name='fred'))
        >>> transaction.commit()
        
        Now ``fred`` is indeed there::
        
        >>> session = Session()
        >>> users = session.query(User).all()
        >>> len(users)
        1
        >>> users[0].name
        u'fred'
        
        And ``bob`` is still in ``site1``::
        
        >>> setSite(site1)
        >>> session = Session()
        >>> users = session.query(User).all()
        >>> len(users)
        1
        >>> users[0].name
        u'bob'
        
        Engines and Threading
        =====================
        
        >>> engine = None
        >>> def setEngine():
        ...     global engine
        ...     engine = engine_factory1()
        
        Engine factories must produce the same engine:
        
        >>> setEngine()
        >>> engine is engine_factory1()
        True
        
        Even if you call it in a different thread:
        
        >>> import threading
        >>> engine = None
        >>> t = threading.Thread(target=setEngine)
        >>> t.start()
        >>> t.join()
        
        >>> engine is engine_factory1()
        True
        
        Unless they are reset:
        
        >>> engine_factory1.reset()
        >>> engine is engine_factory1()
        False
        
        Even engine factories with the same parameters created at (almost) the same
        time should produce different engines:
        
        >>> EngineFactory(TEST_DSN1)() is EngineFactory(TEST_DSN1)()
        False
        
        Configuration using ZCML
        ========================
        
        A configuration directive is provided to register a database engine
        factory using ZCML.
        
        >>> from cStringIO import StringIO
        >>> from zope.configuration import xmlconfig
        >>> import z3c.saconfig
        >>> xmlconfig.XMLConfig('meta.zcml', z3c.saconfig)()
        
        Let's try registering the directory again.
        
        >>> xmlconfig.xmlconfig(StringIO("""
        ... <configure xmlns="http://namespaces.zope.org/db">
        ...   <engine name="dummy" url="sqlite:///:memory:" />
        ... </configure>"""))
        
        >>> component.getUtility(IEngineFactory, name="dummy")
        <z3c.saconfig.utility.EngineFactory object at ...>
        
        This time with a setup call.
        
        >>> xmlconfig.xmlconfig(StringIO("""
        ... <configure xmlns="http://namespaces.zope.org/db">
        ...   <engine name="dummy2" url="sqlite:///:memory:"
        ...           setup="z3c.saconfig.tests.engine_subscriber" />
        ... </configure>"""))
        got: Engine(sqlite:///:memory:)
        
        It's also possible to specify connection pooling options:
        
        >>> xmlconfig.xmlconfig(StringIO("""
        ... <configure xmlns="http://namespaces.zope.org/db">
        ...   <engine name="dummy" url="sqlite:///:memory:"
        ...       pool_size="1"
        ...       max_overflow="2"
        ...       pool_recycle="3"
        ...       pool_timeout="4"
        ...       />
        ... </configure>"""))
        
        >>> engineFactory = component.getUtility(IEngineFactory, name="dummy")
        >>> engineFactory._kw == {'convert_unicode': False, 'echo': None, 'pool_size': 1, 'max_overflow': 2, 'pool_recycle': 3, 'pool_timeout': 4}
        True
        
        (See the SQLAlchemy documentation on connection pooling for details on how
        these arguments are used.)
        
        The session directive is provided to register a scoped session utility:
        
        >>> xmlconfig.xmlconfig(StringIO("""
        ... <configure xmlns="http://namespaces.zope.org/db">
        ...   <session name="dummy" engine="dummy2" />
        ... </configure>"""))
        
        >>> component.getUtility(IScopedSession, name="dummy")
        <z3c.saconfig.utility.GloballyScopedSession object at ...>
        
        >>> from z3c.saconfig import named_scoped_session
        >>> factory = component.getUtility(IEngineFactory, name="dummy2")
        >>> Session = named_scoped_session('dummy')
        >>> Session().bind is factory()
        True
        
        z3c.saconfig
        ************
        
        0.11 (2010-07-05)
        =================
        
        - Add pool_size, max_overflow, pool_recycle and pool_timeout options to the
        <engine /> directive. This allows connection pooling options to be defined
        in ZCML.
        
        - works with sqlalchemy >= 0.5
        (would'nt work with sqlalchemy > 5 prior)
        
        0.10 (2010-01-18)
        =================
        
        - Support current ZTK code
        
        - engine.echo must default to None for SQLAlchemy to honor
        logging.getLogger("sqlalchemy.engine").setLevel(...)
        
        - Do not enable convert_unicode by default. This option changes
        standard SQLAlchemy behaviour by making String type columns return
        unicode data.  This can be especially painful in Zope2 environments
        where unicode is not always accepted.
        
        - Add a convert_unicode option to the zcml engine statement, allowing
        people who need convert_unicode to enable it.
        
        0.9.1 (2009-08-14)
        ==================
        
        - Include documentation on PyPI.
        
        - Small documentation tweaks.
        
        0.9 (2009-08-14)
        ================
        
        - Initial public release.
        
Keywords: zope relational sqlalchemy component integration
Platform: UNKNOWN
Classifier: Development Status :: 4 - Beta
Classifier: Environment :: Web Environment
Classifier: Framework :: Zope3
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: Zope Public License
Classifier: Operating System :: OS Independent
Classifier: Programming Language :: Python
Classifier: Topic :: Internet :: WWW/HTTP
Classifier: Topic :: Software Development :: Libraries
Classifier: Topic :: Database
