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SQLAlchemy/Zope2 transaction integration

Project description


The lead part of the alchemist’s toolkit.

Yes, it’s Yet Another SQLAlchemy/Zope Integration Package. I’m sorry, I really am. Many thanks to Andreas Jung for z3c.sqlalchemy and Kapil Thangavelu for ore.alchemist. I borrowed the Zope transaction data manager code from Andreas who borrowed it from Kapil, I believe.

The purpose of this package is to be the lead part and the lead part only. The gold-making bit is left to SQLAlchemy. That means that are no abstractions or lazy initialisaion or table auto-detection for building SQLAlchemy table metadata and mappers, no generation of Zope 3 interfaces, no CRUD operations, and no dancing polar bears.

You need to understand SQLAlchemy for this package and this README to make any sense. See

Please note that this package is only meant to be used as a tool in other packages; you can not install it directly in a Zope site.

The use case

  • You want SQLAlchemy

  • You want to look up database connections/sessions as named utilities

  • You want to use simple domain/mapper classes, with no particular dependencies

  • You don’t want to worry about transaction and connection handling

  • You want to be able to configure SQL connection parameters at run-time, e.g. in the ZODB. Well, you don’t have to, but it’s nice to have the option.

What you have to do

Let’s say we had some domain classes TableOne and TableTwo, relating to tables table1 and table2.

>>> class TableOne(object):
...     pass
>>> class TableTwo(object):
...     pass

You are supposed to subclass collective.lead.Database, fill in its template methods, and then register the new class as a global, non-persistent named utility providing IDatabase.

>>> from collective.lead import Database
>>> import sqlalchemy as sa
>>> class MyDatabase(Database):
...     @property
...     def _url(self):
...         return sa.engine.url.URL(drivername='mysql', username='user',
...                    host='localhost',  database='testdb')
...     def _setup_tables(self, metadata, tables):
...         tables['table1'] = sa.Table('table1', metadata, autoload=True)
...         tables['table2'] = sa.Table('table2', metadata, autoload=True)
...     def _setup_mappers(self, tables, mappers):
...         mappers['table1'] = sa.mapper(TableOne, tables['table1'])
...         mappers['table2'] = sa.mapper(TableTwo, tables['table2'],
...                                         properties = {
...                                             'table1' : sa.relation(TableOne),
...                                             })

The database utility can now be registered using zcml:


provides=”collective.lead.interfaces.IDatabase” factory=”.database.MyDatabase” name=”my.database” />

or if you prefer directly from python (XXX this does not work):

>>> from zope.component import provideUtility
>>> from collective.lead.interfaces import IDatabase
>>> provideUtility(MyDatabase, name='my.database', provides=IDatabase)

Using the database connection

In application code, you can now get a database engine by name. This engine is threadlocal, and contains a single, cached session. When it is first requested, a new transaction will be begun. This is joined to a Zope transaction, and will commit or roll back as appropriate when the request ends. Or, in other words, it should work more or less as you’d expect and you should not need to worry about transactions (neither Zope nor SQL ones).

>>> from zope.component import getUtility
>>> db = getUtility(IDatabase, name='my.database')
>>> db.session.query(TableOne).list()
>>> db.connection.execute("SELECT * FROM table1")


1.0 - unreleased

  • Initial release [optilude]

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