z3c.sqlalchemy - A SQLAlchemy wrapper for Python/Zope
What is z3c.sqlalchemy?
z3c.sqlalchemy is yet another wrapper around SQLAlchemy. The functionality of the wrapper is basically focused on easy integration with Zope. The wrapper cares about connection handling, optional transaction integration with Zope and wrapper management (caching, introspection). z3c.sqlalchemy gives you flexible control over the mapper creation. Mapper classes can be
- auto-generated (with or without autodetection of table relationships)
- configured by the developer
What z3c.sqlalchemy does not do and won't do:
- no support for Zope 3 schemas
- no support for Archetypes schemas
z3c.sqlachemy just tries to provide you with the basic functionalities you need to write SQLAlchemy-based applications with Zope. Higher-level functionalities like integration with Archetypes/Zope 3 schemas are subject to higher-level frameworks. z3c.sqlalchemy does not address these frameworks.
- Zope 5 or higher
- SQLAlchemy 1.4 or higher
- zope.sqlalchemy 1.2.0 or higher
- Python 3.7 or higher
pip install z3c.sqlalchemy
z3c.sqlalchemy depends on the modules zope.component, zope.schema and zope.interface. If you are using z3c.sqlalchemy in a Python-only environment, ensure the these components have to be installed either as eggs or by setting the PYTHONPATH to a corresponding Zope installation.
from z3c.sqlalchemy import createSAWrapper wrapper = createSAWrapper('postgres://postgres:postgres@host/someDB') session = wrapper.session FormatMapper = wrapper.getMapper('format') # auto-generated mapper for table 'format' for row in session.query(FormatMapper).select(...): print row session.flush() # if necessary
The session will participate automatically in a Zope transaction. The wrapper will call automatically session.flush() upon a transaction commit. Please note that 'wrapper.session' will always return the same session instance within the same transaction and same thread.
For a real-world application you don't want to create a new wrapper for every new request. Instead you want to register a wrapper instance as named utility (ISQLAlchemyWrapper) and lookup up the wrapper (the utility!) by name from within your application. This approach is very similiar to looking up an databases adapter or a ZSQL method through acquisition.
By default "wrapper.getMapper(name)" will always auto-generate a new mapper class by using SQLAlchemy auto-load feature. The drawback of this approach is that the mapper class does not know about relationships to other tables. Assume we have a one-to-many relationship between table A and B and you want z3c.sqlalchemy to generate a mapper that is aware of this relationship. For this purpose you can create a wrapper with a "model" as optional parameter. A model is basically a configuration or a series of hints in order to tell z3c.sqlalchemy how mappers a generated.
from z3c.sqlalchemy import createSAWrapper, Model model = Model() model.add(name='A', relations=('B',)) wrapper = createSAWrapper('postgres://postgres:postgres@host/someDB', model=model) AMapper= wrapper.getMapper('A')
This will generate a mapper AMapper where all instances of AMapper have a property 'B' that relates to all corresponding rows in B (see the SQLAlchemy documentation on mappers, properties and relation()). In this example you define the relationship between A and B explictly through the 'relations' parameter (as a sequence of related table names).
z3c.sqlalchemy also supports the auto-detection of relationships between tables. Unfortunately SQLAlchemy does not support this feature out-of-the-box and in a portable way. Therefore this feature of z3c.sqlalchemy is highly experimental and currently only available for Postgres (tested with Postgres 8.X).:
from z3c.sqlalchemy import createSAWrapper, Model model = Model() model.add(name='A', autodetect_relations=True) wrapper = createSAWrapper('postgres://postgres:postgres@host/someDB', model=model) AMapper= wrapper.getMapper('A')
In this case z3c.sqlalchemy will scan all tables in order to detect relationships automatically and build the mapper class and its properties according to the found relationships. Warning: this feature is experimental and it might take some time to scan all tables before the first request. Currently only Postgres tables in the 'public' schema are supported).
In same cases you might be interested to use your own base classes for a generated mapper. Also this usecase is supported by passing the base class to the model using the 'mapper_class' parameter:
from z3c.sqlalchemy import createSAWrapper, Model from z3c.sqlalchemy.mapper import MappedClassBase class MyAMapper(MappedClassBase): pass model = Model() model.add(name='A', relations=('B',) mapper_class = MyAMapper) wrapper = createSAWrapper('postgres://postgres:postgres@host/someDB', model=model) AMapper= wrapper.getMapper('A') # AMapper will be an instance of MyAMapper
When you are working with wrapper in a Zope environment you are usually interested to to register a wrapper instance as named utility implementing ISQLAlchemyWrapper. You can can perform the registration lazily by passing the name utility as 'name' parameter to the createSAWrapper(..., name='my.postgres.test.db') method.
A convenience method for obtaining a wrapper instance by name is available through getSAWrapper:
createSAWrapper(dsn,..., name='my.name') ... wrapper = getSAWrapper('my.name')
z3c.sqlalchemy was developed with Zope and basically tested against Postgres 7.4.X and 8.X and SQLite 3.3.
Running z3c.sqalchemy against MySQL databases without transaction support might cause trouble upon the implicit commit() operation. For this reason MySQL without transaction support isn't supported right now
z3c.sqlalchemy was written by Andreas Jung for Haufe Mediengruppe, Freiburg, Germany and ZOPYX Ltd. & Co. KG, Tuebingen, Germany.
z3c.sqlalchemy is licensed under the Zope Public License 2.1.
Parts of the code are influenced by z3c.zalchemy (Juergen Kartnaller, Michael Bernstein & others) and Alchemist/ore.alchemist (Kapil Thangavelu). Thanks to Martin Aspeli for giving valuable feedback.