===============================
Notes About Supported Databases
===============================

Django attempts to support as many features as possible on all databases.
However, since not all database servers are identical, there is obviously
going to be some variations. This file describes some of the
features that might relevant to Django usage. It is not intended as a
replacement for server-specific documentation or reference manuals.

MySQL Notes
===========

Django expects the database to support transactions, referential integrity,
and Unicode support (UTF-8 encoding). Fortunately MySQL_ has all these
features as available as far back as 3.23. While it may be possible to use
3.23 or 4.0, you will probably have less trouble if you use 4.1 or 5.0.

MySQL-4.1
---------

MySQL-4.1_ has greatly improved support for character sets. It is possible to
set different default character sets on the database, table, and column.
Previous versions have only a server-wide character set setting. It's also the
first version where the character set can be changed on the fly. 4.1 also has
support for views, but these are not currently used by Django.

MySQL-5.0
---------

MySQL-5.0_ adds the ``information_schema`` database, which contains detailed
data on all database schema. This is used for Django's ``inspectdb`` feature,
when it is available. 5.0 also has support for stored procedures, but these
are not currently used by Django.

.. _MySQL: http://www.mysql.com/
.. _MySQL-4.1: http://dev.mysql.com/doc/refman/4.1/en/index.html
.. _MySQL-5.0: http://dev.mysql.com/doc/refman/5.0/en/index.html

Storage Engines
---------------

MySQL has several `storage engines`_ (previously called table types). You can
change the default storage engine in the server configuration.

The default one is MyISAM_. The main drawback of MyISAM is that it does not
currently have support for transactions or foreign keys. On the plus side, it
is currently the only engine that supports full-text indexing and searching.

The InnoDB_ engine is fully transactional and supports foreign key references.

The BDB_ engine, like InnoDB, is also fully transactional and supports foreign
key references. However, it's use seems to be somewhat deprecated.

`Other storage engines`_, including SolidDB_ and Falcon_, are on the horizon.
For now, InnoDB is probably your best choice.

.. _storage engines: http://dev.mysql.com/doc/refman/5.0/en/storage-engines.html
.. _MyISAM: http://dev.mysql.com/doc/refman/5.0/en/myisam-storage-engine.html
.. _BDB: http://dev.mysql.com/doc/refman/5.0/en/bdb-storage-engine.html
.. _InnoDB: http://dev.mysql.com/doc/refman/5.0/en/innodb.html
.. _Other storage engines: http://dev.mysql.com/doc/refman/5.1/en/storage-engines-other.html
.. _SolidDB: http://forge.mysql.com/projects/view.php?id=139
.. _Falcon: http://dev.mysql.com/doc/falcon/en/index.html

MySQLdb
-------

`MySQLdb`_ is the Python interface to MySQL. 1.2.1 is the first version which
has support for MySQL-4.1 and newer. If you are trying to use an older version
of MySQL, then 1.2.0 *may* work for you.

.. _MySQLdb: http://sourceforge.net/projects/mysql-python

Creating your database
~~~~~~~~~~~~~~~~~~~~~~

You can `create your database`_ using the command-line tools and this SQL::

  CREATE DATABASE <dbname> CHARACTER SET utf8;
  
This ensures all tables and columns will use utf8 by default.
  
.. _create your database: http://dev.mysql.com/doc/refman/5.0/en/create-database.html

Connecting to the database
~~~~~~~~~~~~~~~~~~~~~~~~~~

Refer to the `settings documentation`_.

Connection settings are used in this order:

 1. ``DATABASE_OPTIONS``
 2. ``DATABASE_NAME``, ``DATABASE_USER``, ``DATABASE_PASSWORD``, ``DATABASE_HOST``,
    ``DATABASE_PORT``
 3. MySQL option files.

In other words, if you set the name of the database in ``DATABASE_OPTIONS``,
this will take precedence over ``DATABASE_NAME``, which would override
anything in a `MySQL option file`_.

Here's a sample configuration which uses a MySQL option file::

  # settings.py
  DATABASE_ENGINE = "mysql"
  DATABASE_OPTIONS = {
      'read_default_file': '/path/to/my.cnf',
      }
      
  # my.cnf
  [client]
  database = DATABASE_NAME
  user = DATABASE_USER
  passwd = DATABASE_PASSWORD
  default-character-set = utf8

There are several other MySQLdb connection options which may be useful, such
as ``ssl``, ``use_unicode``, ``init_command``, and ``sql_mode``; consult the
`MySQLdb documentation`_ for more details.
  
.. _settings documentation: http://www.djangoproject.com/documentation/settings/#database-engine
.. _MySQL option file: http://dev.mysql.com/doc/refman/5.0/en/option-files.html
.. _MySQLdb documentation: http://mysql-python.sourceforge.net/

Creating your tables
~~~~~~~~~~~~~~~~~~~~

When Django generates the schema, it doesn't specify a storage engine, so they
will be created with whatever default `storage engine`__ your database server
is configured for. The easiest solution is to set your database server's default
storage engine to the desired engine.

__ `storage engines`_

If you are using a hosting service and can't change your server's default
storage engine, you have a couple of options.

After the tables is created, all that is needed to convert it to a new storage
engine (such as InnoDB) is::
  
  ALTER TABLE <tablename> ENGINE=INNODB;

With a lot of tables, this can be tedious.

Another option is to use the ``init_command`` option for MySQLdb prior to
creating your tables::

  DATABASE_OPTIONS = {
      ...
      "init_command": "SET storage_engine=INNODB",
      ...
      }

This sets the default storage engine upon connecting to the database. After
your tables are set up and running in production, you should remove this
option.

Another method for changing the storage engine is described in
AlterModelOnSyncDB_.

.. _AlterModelOnSyncDB: http://code.djangoproject.com/wiki/AlterModelOnSyncDB

