===============================

Notes about supported databases

===============================

Django attempts to support as many features as possible on all database

backends. However, not all database backends are alike, and we've had to make

design decisions on which features to support and which assumptions we can make

safely.

This file describes some of the features that might be relevant to Django

usage. Of course, 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'll 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 Django currently doesn't use views.

MySQL 5.0

---------

`MySQL 5.0`_ adds the ``information_schema`` database, which contains detailed

data on all database schema. Django's ``inspectdb`` feature uses this

``information_schema`` if it's available. 5.0 also has support for stored

procedures, but Django currently doesn't use stored procedures.

.. _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 engine is MyISAM_. The main drawback of MyISAM is that it doesn't

currently support transactions or foreign keys. On the plus side, it's

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, its use seems to be 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 that

has support for MySQL 4.1 and newer. If you are trying to use an older version

of MySQL, then 1.2.0 *might* 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 UTF-8 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

Several other MySQLdb connection options 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

tables 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.

If you're using a hosting service and can't change your server's default

storage engine, you have a couple of options.

    * After the tables are created, execute an ``ALTER TABLE`` statement to

      convert a table to a new storage engine (such as InnoDB)::

          ALTER TABLE <tablename> ENGINE=INNODB;

      This can be tedious if you have a lot of tables.

    * 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 have been created, you should remove this option.

    * Another method for changing the storage engine is described in

      AlterModelOnSyncDB_.

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