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.

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.

MySQLdb

MySQLdb is the Python interface to MySQL. Version 1.2.1p2 or later is required for full MySQL support in Django. Earlier versions will not work with the mysql backend.

If you are trying to use an older version of MySQL and the mysql_old backend, then 1.2.0 might work for you.

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.

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
password = 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.

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.

Connecting to the database

Your Django settings.py file should look something like this for Oracle:

DATABASE_ENGINE = 'oracle'
DATABASE_NAME = 'xe'
DATABASE_USER = 'a_user'
DATABASE_PASSWORD = 'a_password'
DATABASE_HOST = ''
DATABASE_PORT = ''

If you don’t use a tnsnames.ora file or a similar naming method that recognizes the SID (“xe” in this example), then fill in both DATABASE_HOST and DATABASE_PORT like so:

DATABASE_ENGINE = 'oracle'
DATABASE_NAME = 'xe'
DATABASE_USER = 'a_user'
DATABASE_PASSWORD = 'a_password'
DATABASE_HOST = 'dbprod01ned.mycompany.com'
DATABASE_PORT = '1540'

You should supply both DATABASE_HOST and DATABASE_PORT, or leave both as empty strings.

Tablespace options

A common paradigm for optimizing performance in Oracle-based systems is the use of tablespaces to organize disk layout. The Oracle backend supports this use case by adding db_tablespace options to the Meta and Field classes. (When you use a backend that lacks support for tablespaces, Django ignores these options.)

A tablespace can be specified for the table(s) generated by a model by supplying the db_tablespace option inside the model’s class Meta. Additionally, you can pass the db_tablespace option to a Field constructor to specify an alternate tablespace for the Field‘s column index. If no index would be created for the column, the db_tablespace option is ignored.

class TablespaceExample(models.Model):
    name = models.CharField(max_length=30, db_index=True, db_tablespace="indexes")
    data = models.CharField(max_length=255, db_index=True)
    edges = models.ManyToManyField(to="self", db_tablespace="indexes")

    class Meta:
        db_tablespace = "tables"

In this example, the tables generated by the TablespaceExample model (i.e., the model table and the many-to-many table) would be stored in the tables tablespace. The index for the name field and the indexes on the many-to-many table would be stored in the indexes tablespace. The data field would also generate an index, but no tablespace for it is specified, so it would be stored in the model tablespace tables by default.

New in the Django development version: Use the DEFAULT_TABLESPACE and DEFAULT_INDEX_TABLESPACE settings to specify default values for the db_tablespace options. These are useful for setting a tablespace for the built-in Django apps and other applications whose code you cannot control.

Django does not create the tablespaces for you. Please refer to Oracle’s documentation for details on creating and managing tablespaces.

Naming issues

Oracle imposes a name length limit of 30 characters. To accommodate this, the backend truncates database identifiers to fit, replacing the final four characters of the truncated name with a repeatable MD5 hash value.

NULL and empty strings

Django generally prefers to use the empty string (‘’) rather than NULL, but Oracle treats both identically. To get around this, the Oracle backend coerces the null=True option on fields that permit the empty string as a value. When fetching from the database, it is assumed that a NULL value in one of these fields really means the empty string, and the data is silently converted to reflect this assumption.

TextField limitations

The Oracle backend stores TextFields as NCLOB columns. Oracle imposes some limitations on the usage of such LOB columns in general:

• LOB columns may not be used as primary keys.
• LOB columns may not be used in indexes.
• LOB columns may not be used in a SELECT DISTINCT list. This means that attempting to use the QuerySet.distinct method on a model that includes TextField columns will result in an error when run against Oracle. A workaround to this is to keep TextField columns out of any models that you foresee performing distinct() queries on, and to include the TextField in a related model instead.