zope.sqlalchemy 1.0

Introduction

The aim of this package is to unify the plethora of existing packages integrating SQLAlchemy with Zope’s transaction management. As such it seeks only to provide a data manager and makes no attempt to define a zopeish way to configure engines.

For WSGI applications, Zope style automatic transaction management is available with repoze.tm2 (used by Turbogears 2 and other systems).

This package is also used by pyramid_tm (an add-on of the Pyramid) web framework.

You need to understand SQLAlchemy and the Zope transaction manager for this package and this README to make any sense.

Running the tests

This package is distributed as a buildout. Using your desired python run:

$ python bootstrap.py $ ./bin/buildout

This will download the dependent packages and setup the test script, which may be run with:

$ ./bin/test

or with the standard setuptools test command:

$ ./bin/py setup.py test

To enable testing with your own database set the TEST_DSN environment variable to your sqlalchemy database dsn. Two-phase commit behaviour may be tested by setting the TEST_TWOPHASE variable to a non empty string. e.g:

$ TEST_DSN=postgres://test:test@localhost/test TEST_TWOPHASE=True bin/test

Example

This example is lifted directly from the SQLAlchemy declarative documentation. First the necessary imports.

>>> from sqlalchemy import *
>>> from sqlalchemy.ext.declarative import declarative_base
>>> from sqlalchemy.orm import scoped_session, sessionmaker, relation
>>> from zope.sqlalchemy import ZopeTransactionExtension
>>> import transaction

Now to define the mapper classes.

>>> 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'))

Create an engine and setup the tables. Note that for this example to work a recent version of sqlite/pysqlite is required. 3.4.0 seems to be sufficient.

>>> engine = create_engine(TEST_DSN, convert_unicode=True)
>>> Base.metadata.create_all(engine)

Now to create the session itself. As zope is a threaded web server we must use scoped sessions. Zope and SQLAlchemy sessions are tied together by using the ZopeTransactionExtension from this package.

>>> Session = scoped_session(sessionmaker(bind=engine,
... twophase=TEST_TWOPHASE, extension=ZopeTransactionExtension()))

Call the scoped session factory to retrieve a session. You may call this as many times as you like within a transaction and you will always retrieve the same session. At present there are no users in the database.

>>> session = Session()
>>> session.query(User).all()
[]

We can now create a new user and commit the changes using Zope’s transaction machinery, just as Zope’s publisher would.

>>> session.add(User(id=1, name='bob'))
>>> transaction.commit()

Engine level connections are outside the scope of the transaction integration.

>>> engine.connect().execute('SELECT * FROM test_users').fetchall()
[(1, ...'bob')]

A new transaction requires a new session. Let’s add an address.

>>> session = Session()
>>> bob = session.query(User).all()[0]
>>> str(bob.name)
'bob'
>>> bob.addresses
[]
>>> bob.addresses.append(Address(id=1, email='bob@bob.bob'))
>>> transaction.commit()
>>> session = Session()
>>> bob = session.query(User).all()[0]
>>> bob.addresses
[<Address object at ...>]
>>> str(bob.addresses[0].email)
'bob@bob.bob'
>>> bob.addresses[0].email = 'wrong@wrong'

To rollback a transaction, use transaction.abort().

>>> transaction.abort()
>>> session = Session()
>>> bob = session.query(User).all()[0]
>>> str(bob.addresses[0].email)
'bob@bob.bob'
>>> transaction.abort()

By default, zope.sqlalchemy puts sessions in an ‘active’ state when they are first used. ORM write operations automatically move the session into a ‘changed’ state. This avoids unnecessary database commits. Sometimes it is necessary to interact with the database directly through SQL. It is not possible to guess whether such an operation is a read or a write. Therefore we must manually mark the session as changed when manual SQL statements write to the DB.

>>> session = Session()
>>> conn = session.connection()
>>> users = Base.metadata.tables['test_users']
>>> conn.execute(users.update(users.c.name=='bob'), name='ben')
<sqlalchemy.engine...ResultProxy object at ...>
>>> from zope.sqlalchemy import mark_changed
>>> mark_changed(session)
>>> transaction.commit()
>>> session = Session()
>>> str(session.query(User).all()[0].name)
'ben'
>>> transaction.abort()

If this is a problem you may tell the extension to place the session in the ‘changed’ state initially.

>>> Session.remove()
>>> Session.configure(extension=ZopeTransactionExtension('changed'))
>>> session = Session()
>>> conn = session.connection()
>>> conn.execute(users.update(users.c.name=='ben'), name='bob')
<sqlalchemy.engine...ResultProxy object at ...>
>>> transaction.commit()
>>> session = Session()
>>> str(session.query(User).all()[0].name)
'bob'
>>> transaction.abort()

Registration Using SQLAlchemy Events

The zope.sqlalchemy.register() function performs the same function as the ZopeTransactionExtension, except makes use of the newer SQLAlchemy event system which superseded the extension system as of SQLAlchemy 0.7. Usage is similar:

>>> from zope.sqlalchemy import register
>>> Session = scoped_session(sessionmaker(bind=engine,
... twophase=TEST_TWOPHASE))
>>> register(Session, keep_session=True)
>>> session = Session()
>>> jack = User(id=2, name='jack')
>>> session.add(jack)
>>> transaction.commit()
>>> engine.execute("select name from test_users where id=2").scalar()
u'jack'

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