Minimal Zope/SQLAlchemy transaction integration
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.
You need to understand SQLAlchemy for this package and this README to make any sense. See http://sqlalchemy.org/docs/.
This package is distributed as a buildout. Using your desired python run:
$ python bootstrap.py
This will download the dependent packages and setup the test script, which may be run with:
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
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.
>>> if SA_0_5: ... Session = scoped_session(sessionmaker(bind=engine, ... twophase=TEST_TWOPHASE, extension=ZopeTransactionExtension()))
The exact arguments depend on the version. Under SQLAlchemy 0.4 we must also supply transactional=True (equivalent to autocommit=False, which is default under 0.5).
>>> if SA_0_4: ... Session = scoped_session(sessionmaker(bind=engine, ... twophase=TEST_TWOPHASE, extension=ZopeTransactionExtension(), ... transactional=True, autoflush=True,))
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 machinary, just as Zope’s publisher would.
>>> session.add(User(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() >>> bob.name u'bob' >>> bob.addresses  >>> bob.addresses.append(Address(firstname.lastname@example.org')) >>> transaction.commit() >>> session = Session() >>> bob = session.query(User).all() >>> bob.addresses [<Address object at ...>] >>> bob.addresses.email email@example.com' >>> bob.addresses.email = 'wrong@wrong'
To rollback a transaction, use transaction.abort().
>>> transaction.abort() >>> session = Session() >>> bob = session.query(User).all() >>> bob.addresses.email firstname.lastname@example.org' >>> 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.base.ResultProxy object at ...> >>> from zope.sqlalchemy import mark_changed >>> mark_changed(session) >>> transaction.commit() >>> session = Session() >>> session.query(User).all().name u'ben' >>> transaction.abort()
If this is a problem you may tell the extension to place the session in the ‘changed’ state initially.
>>> Session.configure(extension=ZopeTransactionExtension('changed')) >>> Session.remove() >>> session = Session() >>> conn = session.connection() >>> conn.execute(users.update(users.c.name=='ben'), name='bob') <sqlalchemy.engine.base.ResultProxy object at ...> >>> transaction.commit() >>> session = Session() >>> session.query(User).all().name u'bob' >>> transaction.abort()
- Only raise errors in tpc_abort if we have committed.
- Remove the session id from the SESSION_STATE just before we de-reference the session (i.e. all work is already successfuly completed). This fixes cases where the transaction commit failed but SESSION_STATE was already cleared. In those cases, the transaction was wedeged as abort would always error. This happened on PostgreSQL where invalid SQL was used and the error caught.
- Call session.flush() unconditionally in tpc_begin.
- Change error message on session.commit() to be friendlier to non zope users.
- Support for bulk update and delete with SQLAlchemy 0.5.1
- New objects added to a session did not cause a transaction join, so were not committed at the end of the transaction unless the database was accessed. SQLAlchemy 0.4.7 or 0.5beta3 now required.
- For correctness and consistency with ZODB, renamed the function ‘invalidate’ to ‘mark_changed’ and the status ‘invalidated’ to ‘changed’.
- Updated to support SQLAlchemy 0.5. (0.4.6 is still supported).
- Initial public release.
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