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.
In :ref:`orm_toplevel`, the Object Relational Mapper is introduced and fully described. New users should begin with the :ref:`ormtutorial_toplevel`. 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 :ref:`core_toplevel`, 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 :ref:`sqlexpression_toplevel`. SQLAlchemy engine, connection, and pooling services are also described in :ref:`core_toplevel`.
In :ref:`dialect_toplevel`, reference documentation for all provided database and DBAPI backends is provided.
Working code examples, mostly regarding the ORM, are included in the SQLAlchemy distribution. A description of all the included example applications is at :ref:`examples_toplevel`.
There is also a wide variety of examples involving both core SQLAlchemy constructs as well as the ORM on the wiki. See Theatrum Chemicum.
SQLAlchemy has been tested against the following platforms:
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 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.
It is strongly recommended that either setuptools or distribute be installed. Python's built-in distutils lacks many widely used installation features.
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:
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
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
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__ # doctest: +SKIP 0.8.0
0.7 to 0.8 Migration
Notes on what's changed from 0.7 to 0.8 is available on the SQLAlchemy wiki at 08Migration.