SQLAlchemy 0.8 Documentation
Overview¶
Overview¶
The SQLAlchemy SQL Toolkit and Object Relational Mapper is a comprehensive set of tools for working with databases and Python. It has several distinct areas of functionality which can be used individually or combined together. Its major components are illustrated in below, with component dependencies organized into layers:
Above, the two most significant front-facing portions of SQLAlchemy are the Object Relational Mapper and the SQL Expression Language. SQL Expressions can be used independently of the ORM. When using the ORM, the SQL Expression language remains part of the public facing API as it is used within object-relational configurations and queries.
Documentation Overview¶
The documentation is separated into three sections: SQLAlchemy ORM, SQLAlchemy Core, and Dialects.
In SQLAlchemy ORM, the Object Relational Mapper is introduced and fully described. New users should begin with the Object Relational Tutorial. If you want to work with higher-level SQL which is constructed automatically for you, as well as management of Python objects, proceed to this tutorial.
In SQLAlchemy Core, the breadth of SQLAlchemy’s SQL and database integration and description services are documented, the core of which is the SQL Expression language. The SQL Expression Language is a toolkit all its own, independent of the ORM package, which can be used to construct manipulable SQL expressions which can be programmatically constructed, modified, and executed, returning cursor-like result sets. In contrast to the ORM’s domain-centric mode of usage, the expression language provides a schema-centric usage paradigm. New users should begin here with SQL Expression Language Tutorial. SQLAlchemy engine, connection, and pooling services are also described in SQLAlchemy Core.
In Dialects, reference documentation for all provided database and DBAPI backends is provided.
Code Examples¶
Working code examples, mostly regarding the ORM, are included in the SQLAlchemy distribution. A description of all the included example applications is at Examples.
There is also a wide variety of examples involving both core SQLAlchemy constructs as well as the ORM on the wiki. See Theatrum Chemicum.
Installation Guide¶
Supported Platforms¶
SQLAlchemy has been tested against the following platforms:
- cPython since version 2.5, through the 2.xx series
- cPython version 3, throughout all 3.xx series
- Jython 2.5 or greater
- Pypy 1.5 or greater
Changed in version 0.8: Python 2.5 is now the minimum Python version supported.
Supported Installation Methods¶
SQLAlchemy supports installation using standard Python “distutils” or “setuptools” methodologies. An overview of potential setups is as follows:
- Plain Python Distutils - SQLAlchemy can be installed with a clean Python install using the services provided via Python Distutils, using the setup.py script. The C extensions as well as Python 3 builds are supported.
- Standard Setuptools - When using setuptools, SQLAlchemy can be installed via setup.py or easy_install, and the C extensions are supported. setuptools is not supported on Python 3 at the time of this writing.
- Distribute - With distribute, SQLAlchemy can be installed via setup.py or easy_install, and the C extensions as well as Python 3 builds are supported.
- pip - pip is an installer that rides on top of setuptools or distribute, replacing the usage of easy_install. It is often preferred for its simpler mode of usage.
Install via easy_install or pip¶
When easy_install or pip is available, the distribution can be downloaded from Pypi and installed in one step:
easy_install SQLAlchemy
Or with pip:
pip install SQLAlchemy
This command will download the latest version of SQLAlchemy from the Python Cheese Shop and install it to your system.
Installing using setup.py¶
Otherwise, you can install from the distribution using the setup.py script:
python setup.py install
Installing the C Extensions¶
SQLAlchemy includes C extensions which provide an extra speed boost for dealing with result sets. Currently, the extensions are only supported on the 2.xx series of cPython, not Python 3 or Pypy.
setup.py will automatically build the extensions if an appropriate platform is detected. If the build of the C extensions fails, due to missing compiler or other issue, the setup process will output a warning message, and re-run the build without the C extensions, upon completion reporting final status.
To run the build/install without even attempting to compile the C extensions, pass the flag --without-cextensions to the setup.py script:
python setup.py --without-cextensions install
Or with pip:
pip install --global-option='--without-cextensions' SQLAlchemy
Note
The --without-cextensions flag is available only if setuptools or distribute is installed. It is not available on a plain Python distutils installation. The library will still install without the C extensions if they cannot be built, however.
Installing on Python 3¶
SQLAlchemy ships as Python 2 code. For Python 3 usage, the setup.py script will invoke the Python 2to3 tool on the build, plugging in an extra “preprocessor” as well. The 2to3 step works with Python distutils (part of the standard Python install) and Distribute - it will not work with a non-Distribute setuptools installation.
Installing a Database API¶
SQLAlchemy is designed to operate with a DBAPI implementation built for a particular database, and includes support for the most popular databases. The individual database sections in Dialects enumerate the available DBAPIs for each database, including external links.
Checking the Installed SQLAlchemy Version¶
This documentation covers SQLAlchemy version 0.8. If you’re working on a system that already has SQLAlchemy installed, check the version from your Python prompt like this:
>>> import sqlalchemy
>>> sqlalchemy.__version__
0.8.00.7 to 0.8 Migration¶
Notes on what’s changed from 0.7 to 0.8 is available here at What’s New in SQLAlchemy 0.8?.