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<div class="yui-g" id="ref-databases">
<div class="section" id="s-databases">
<span id="databases"></span><h1>Databases<a class="headerlink" href="#databases" title="Permalink to this headline">¶</a></h1>
<p>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.</p>
<p>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.</p>
<div class="section" id="s-postgresql-notes">
<span id="s-id1"></span><span id="postgresql-notes"></span><span id="id1"></span><h2>PostgreSQL notes<a class="headerlink" href="#postgresql-notes" title="Permalink to this headline">¶</a></h2>
<div class="versionchanged">
<span class="title">Changed in Django 1.4:</span> <a class="reference internal" href="../releases/1.4.html"><em>Please see the release notes</em></a></div>
<p>Django supports PostgreSQL 8.2 and higher.</p>
<div class="section" id="s-postgresql-8-2-to-8-2-4">
<span id="postgresql-8-2-to-8-2-4"></span><h3>PostgreSQL 8.2 to 8.2.4<a class="headerlink" href="#postgresql-8-2-to-8-2-4" title="Permalink to this headline">¶</a></h3>
<p>The implementation of the population statistics aggregates <tt class="docutils literal"><span class="pre">STDDEV_POP</span></tt> and
<tt class="docutils literal"><span class="pre">VAR_POP</span></tt> that shipped with PostgreSQL 8.2 to 8.2.4 are <a class="reference external" href="http://archives.postgresql.org/pgsql-bugs/2007-07/msg00046.php">known to be
faulty</a>. Users of these releases of PostgreSQL are advised to upgrade to
<a class="reference external" href="http://www.postgresql.org/docs/devel/static/release-8-2-5.html">Release 8.2.5</a> or later. Django will raise a <tt class="docutils literal"><span class="pre">NotImplementedError</span></tt> if you
attempt to use the <tt class="docutils literal"><span class="pre">StdDev(sample=False)</span></tt> or <tt class="docutils literal"><span class="pre">Variance(sample=False)</span></tt>
aggregate with a database backend that falls within the affected release range.</p>
</div>
<div class="section" id="s-optimizing-postgresql-s-configuration">
<span id="optimizing-postgresql-s-configuration"></span><h3>Optimizing PostgreSQL’s configuration<a class="headerlink" href="#optimizing-postgresql-s-configuration" title="Permalink to this headline">¶</a></h3>
<p>Django needs the following parameters for its database connections:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">client_encoding</span></tt>: <tt class="docutils literal"><span class="pre">'UTF8'</span></tt>,</li>
<li><tt class="docutils literal"><span class="pre">default_transaction_isolation</span></tt>: <tt class="docutils literal"><span class="pre">'read</span> <span class="pre">committed'</span></tt>,</li>
<li><tt class="docutils literal"><span class="pre">timezone</span></tt>: <tt class="docutils literal"><span class="pre">'UTC'</span></tt> when <a class="reference internal" href="settings.html#std:setting-USE_TZ"><tt class="xref std std-setting docutils literal"><span class="pre">USE_TZ</span></tt></a> is <tt class="docutils literal"><span class="pre">True</span></tt>, value of
<a class="reference internal" href="settings.html#std:setting-TIME_ZONE"><tt class="xref std std-setting docutils literal"><span class="pre">TIME_ZONE</span></tt></a> otherwise.</li>
</ul>
<p>If these parameters already have the correct values, Django won’t set them for
every new connection, which improves performance slightly. You can configure
them directly in <tt class="file docutils literal"><span class="pre">postgresql.conf</span></tt> or more conveniently per database
user with <a class="reference external" href="http://www.postgresql.org/docs/current/interactive/sql-alterrole.html">ALTER ROLE</a>.</p>
<p>Django will work just fine without this optimization, but each new connection
will do some additional queries to set these parameters.</p>
</div>
<div class="section" id="s-transaction-handling">
<span id="transaction-handling"></span><h3>Transaction handling<a class="headerlink" href="#transaction-handling" title="Permalink to this headline">¶</a></h3>
<p><a class="reference internal" href="../topics/db/transactions.html"><em>By default</em></a>, Django runs with an open
transaction which it commits automatically when any built-in, data-altering
model function is called. The PostgreSQL backends normally operate the same as
any other Django backend in this respect.</p>
<div class="section" id="s-autocommit-mode">
<span id="s-postgresql-autocommit-mode"></span><span id="autocommit-mode"></span><span id="postgresql-autocommit-mode"></span><h4>Autocommit mode<a class="headerlink" href="#autocommit-mode" title="Permalink to this headline">¶</a></h4>
<p>If your application is particularly read-heavy and doesn’t make many
database writes, the overhead of a constantly open transaction can
sometimes be noticeable. For those situations, you can configure Django
to use <em>“autocommit”</em> behavior for the connection, meaning that each database
operation will normally be in its own transaction, rather than having
the transaction extend over multiple operations. In this case, you can
still manually start a transaction if you’re doing something that
requires consistency across multiple database operations. The
autocommit behavior is enabled by setting the <tt class="docutils literal"><span class="pre">autocommit</span></tt> key in
the <a class="reference internal" href="settings.html#std:setting-OPTIONS"><tt class="xref std std-setting docutils literal"><span class="pre">OPTIONS</span></tt></a> part of your database configuration in
<a class="reference internal" href="settings.html#std:setting-DATABASES"><tt class="xref std std-setting docutils literal"><span class="pre">DATABASES</span></tt></a>:</p>
<div class="highlight-python"><pre>'OPTIONS': {
'autocommit': True,
}</pre>
</div>
<p>In this configuration, Django still ensures that <a class="reference internal" href="../topics/db/queries.html#topics-db-queries-delete"><em>delete()</em></a> and <a class="reference internal" href="../topics/db/queries.html#topics-db-queries-update"><em>update()</em></a>
queries run inside a single transaction, so that either all the affected
objects are changed or none of them are.</p>
<div class="admonition-this-is-database-level-autocommit admonition">
<p class="first admonition-title">This is database-level autocommit</p>
<p class="last">This functionality is not the same as the <a class="reference internal" href="../topics/db/transactions.html#topics-db-transactions-autocommit"><em>autocommit</em></a> decorator. That decorator is
a Django-level implementation that commits automatically after
data changing operations. The feature enabled using the
<a class="reference internal" href="settings.html#std:setting-OPTIONS"><tt class="xref std std-setting docutils literal"><span class="pre">OPTIONS</span></tt></a> option provides autocommit behavior at the
database adapter level. It commits after <em>every</em> operation.</p>
</div>
<p>If you are using this feature and performing an operation akin to delete or
updating that requires multiple operations, you are strongly recommended to
wrap you operations in manual transaction handling to ensure data consistency.
You should also audit your existing code for any instances of this behavior
before enabling this feature. It’s faster, but it provides less automatic
protection for multi-call operations.</p>
</div>
<div class="section" id="s-indexes-for-varchar-and-text-columns">
<span id="indexes-for-varchar-and-text-columns"></span><h4>Indexes for <tt class="docutils literal"><span class="pre">varchar</span></tt> and <tt class="docutils literal"><span class="pre">text</span></tt> columns<a class="headerlink" href="#indexes-for-varchar-and-text-columns" title="Permalink to this headline">¶</a></h4>
<p>When specifying <tt class="docutils literal"><span class="pre">db_index=True</span></tt> on your model fields, Django typically
outputs a single <tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">INDEX</span></tt> statement. However, if the database type
for the field is either <tt class="docutils literal"><span class="pre">varchar</span></tt> or <tt class="docutils literal"><span class="pre">text</span></tt> (e.g., used by <tt class="docutils literal"><span class="pre">CharField</span></tt>,
<tt class="docutils literal"><span class="pre">FileField</span></tt>, and <tt class="docutils literal"><span class="pre">TextField</span></tt>), then Django will create
an additional index that uses an appropriate <a class="reference external" href="http://www.postgresql.org/docs/8.4/static/indexes-opclass.html">PostgreSQL operator class</a>
for the column. The extra index is necessary to correctly perfrom
lookups that use the <tt class="docutils literal"><span class="pre">LIKE</span></tt> operator in their SQL, as is done with the
<tt class="docutils literal"><span class="pre">contains</span></tt> and <tt class="docutils literal"><span class="pre">startswith</span></tt> lookup types.</p>
</div>
</div>
</div>
<div class="section" id="s-mysql-notes">
<span id="s-id2"></span><span id="mysql-notes"></span><span id="id2"></span><h2>MySQL notes<a class="headerlink" href="#mysql-notes" title="Permalink to this headline">¶</a></h2>
<p>Django expects the database to support transactions, referential integrity, and
Unicode (UTF-8 encoding). Fortunately, <a class="reference external" href="http://www.mysql.com/">MySQL</a> 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.</p>
<div class="section" id="s-mysql-4-1">
<span id="mysql-4-1"></span><h3>MySQL 4.1<a class="headerlink" href="#mysql-4-1" title="Permalink to this headline">¶</a></h3>
<p><a class="reference external" href="http://dev.mysql.com/doc/refman/4.1/en/index.html">MySQL 4.1</a> 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.</p>
</div>
<div class="section" id="s-mysql-5-0">
<span id="mysql-5-0"></span><h3>MySQL 5.0<a class="headerlink" href="#mysql-5-0" title="Permalink to this headline">¶</a></h3>
<p><a class="reference external" href="http://dev.mysql.com/doc/refman/5.0/en/index.html">MySQL 5.0</a> adds the <tt class="docutils literal"><span class="pre">information_schema</span></tt> database, which contains detailed
data on all database schema. Django’s <tt class="docutils literal"><span class="pre">inspectdb</span></tt> feature uses this
<tt class="docutils literal"><span class="pre">information_schema</span></tt> if it’s available. 5.0 also has support for stored
procedures, but Django currently doesn’t use stored procedures.</p>
</div>
<div class="section" id="s-storage-engines">
<span id="s-mysql-storage-engines"></span><span id="storage-engines"></span><span id="mysql-storage-engines"></span><h3>Storage engines<a class="headerlink" href="#storage-engines" title="Permalink to this headline">¶</a></h3>
<p>MySQL has several <a class="reference external" href="http://dev.mysql.com/doc/refman/5.5/en/storage-engines.html">storage engines</a> (previously called table types). You can
change the default storage engine in the server configuration.</p>
<p>Until MySQL 5.5.4, the default engine was <a class="reference external" href="http://dev.mysql.com/doc/refman/5.5/en/myisam-storage-engine.html">MyISAM</a> <a class="footnote-reference" href="#id7" id="id5">[1]</a>. The main drawbacks of
MyISAM are that it doesn’t support transactions or enforce foreign-key
constraints. On the plus side, it’s currently the only engine that supports
full-text indexing and searching.</p>
<p>Since MySQL 5.5.5, the default storage engine is <a class="reference external" href="http://dev.mysql.com/doc/refman/5.5/en/innodb.html">InnoDB</a>. This engine is fully
transactional and supports foreign key references. It’s probably the best
choice at this point.</p>
<p>If you upgrade an existing project to MySQL 5.5.5 and subsequently add some
tables, ensure that your tables are using the same storage engine (i.e. MyISAM
vs. InnoDB). Specifically, if tables that have a <tt class="docutils literal"><span class="pre">ForeignKey</span></tt> between them
use different storage engines, you may see an error like the following when
running <tt class="docutils literal"><span class="pre">syncdb</span></tt>:</p>
<div class="highlight-python"><pre>_mysql_exceptions.OperationalError: (
1005, "Can't create table '\\db_name\\.#sql-4a8_ab' (errno: 150)"
)</pre>
</div>
<div class="versionchanged">
<span class="title">Changed in Django 1.4:</span> <a class="reference internal" href="../releases/1.4.html"><em>Please see the release notes</em></a></div>
<p>In previous versions of Django, fixtures with forward references (i.e.
relations to rows that have not yet been inserted into the database) would fail
to load when using the InnoDB storage engine. This was due to the fact that InnoDB
deviates from the SQL standard by checking foreign key constraints immediately
instead of deferring the check until the transaction is committed. This
problem has been resolved in Django 1.4. Fixture data is now loaded with foreign key
checks turned off; foreign key checks are then re-enabled when the data has
finished loading, at which point the entire table is checked for invalid foreign
key references and an <cite>IntegrityError</cite> is raised if any are found.</p>
<table class="docutils footnote" frame="void" id="id7" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id5">[1]</a></td><td>Unless this was changed by the packager of your MySQL package. We’ve
had reports that the Windows Community Server installer sets up InnoDB as
the default storage engine, for example.</td></tr>
</tbody>
</table>
</div>
<div class="section" id="s-mysqldb">
<span id="mysqldb"></span><h3>MySQLdb<a class="headerlink" href="#mysqldb" title="Permalink to this headline">¶</a></h3>
<p><a class="reference external" href="http://sourceforge.net/projects/mysql-python">MySQLdb</a> is the Python interface to MySQL. Version 1.2.1p2 or later is
required for full MySQL support in Django.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you see <tt class="docutils literal"><span class="pre">ImportError:</span> <span class="pre">cannot</span> <span class="pre">import</span> <span class="pre">name</span> <span class="pre">ImmutableSet</span></tt> when trying to
use Django, your MySQLdb installation may contain an outdated <tt class="docutils literal"><span class="pre">sets.py</span></tt>
file that conflicts with the built-in module of the same name from Python
2.4 and later. To fix this, verify that you have installed MySQLdb version
1.2.1p2 or newer, then delete the <tt class="docutils literal"><span class="pre">sets.py</span></tt> file in the MySQLdb
directory that was left by an earlier version.</p>
</div>
</div>
<div class="section" id="s-creating-your-database">
<span id="creating-your-database"></span><h3>Creating your database<a class="headerlink" href="#creating-your-database" title="Permalink to this headline">¶</a></h3>
<p>You can <a class="reference external" href="http://dev.mysql.com/doc/refman/5.0/en/create-database.html">create your database</a> using the command-line tools and this SQL:</p>
<div class="highlight-python"><pre>CREATE DATABASE <dbname> CHARACTER SET utf8;</pre>
</div>
<p>This ensures all tables and columns will use UTF-8 by default.</p>
<div class="section" id="s-collation-settings">
<span id="s-mysql-collation"></span><span id="collation-settings"></span><span id="mysql-collation"></span><h4>Collation settings<a class="headerlink" href="#collation-settings" title="Permalink to this headline">¶</a></h4>
<p>The collation setting for a column controls the order in which data is sorted
as well as what strings compare as equal. It can be set on a database-wide
level and also per-table and per-column. This is <a class="reference external" href="http://dev.mysql.com/doc/refman/5.0/en/charset.html">documented thoroughly</a> in
the MySQL documentation. In all cases, you set the collation by directly
manipulating the database tables; Django doesn’t provide a way to set this on
the model definition.</p>
<p>By default, with a UTF-8 database, MySQL will use the
<tt class="docutils literal"><span class="pre">utf8_general_ci_swedish</span></tt> collation. This results in all string equality
comparisons being done in a <em>case-insensitive</em> manner. That is, <tt class="docutils literal"><span class="pre">"Fred"</span></tt> and
<tt class="docutils literal"><span class="pre">"freD"</span></tt> are considered equal at the database level. If you have a unique
constraint on a field, it would be illegal to try to insert both <tt class="docutils literal"><span class="pre">"aa"</span></tt> and
<tt class="docutils literal"><span class="pre">"AA"</span></tt> into the same column, since they compare as equal (and, hence,
non-unique) with the default collation.</p>
<p>In many cases, this default will not be a problem. However, if you really want
case-sensitive comparisons on a particular column or table, you would change
the column or table to use the <tt class="docutils literal"><span class="pre">utf8_bin</span></tt> collation. The main thing to be
aware of in this case is that if you are using MySQLdb 1.2.2, the database
backend in Django will then return bytestrings (instead of unicode strings) for
any character fields it receive from the database. This is a strong variation
from Django’s normal practice of <em>always</em> returning unicode strings. It is up
to you, the developer, to handle the fact that you will receive bytestrings if
you configure your table(s) to use <tt class="docutils literal"><span class="pre">utf8_bin</span></tt> collation. Django itself should
mostly work smoothly with such columns (except for the <tt class="docutils literal"><span class="pre">contrib.sessions</span></tt>
<tt class="docutils literal"><span class="pre">Session</span></tt> and <tt class="docutils literal"><span class="pre">contrib.admin</span></tt> <tt class="docutils literal"><span class="pre">LogEntry</span></tt> tables described below), but
your code must be prepared to call <tt class="docutils literal"><span class="pre">django.utils.encoding.smart_unicode()</span></tt> at
times if it really wants to work with consistent data – Django will not do
this for you (the database backend layer and the model population layer are
separated internally so the database layer doesn’t know it needs to make this
conversion in this one particular case).</p>
<p>If you’re using MySQLdb 1.2.1p2, Django’s standard
<a class="reference internal" href="models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><tt class="xref py py-class docutils literal"><span class="pre">CharField</span></tt></a> class will return unicode strings even
with <tt class="docutils literal"><span class="pre">utf8_bin</span></tt> collation. However, <a class="reference internal" href="models/fields.html#django.db.models.TextField" title="django.db.models.TextField"><tt class="xref py py-class docutils literal"><span class="pre">TextField</span></tt></a>
fields will be returned as an <tt class="docutils literal"><span class="pre">array.array</span></tt> instance (from Python’s standard
<tt class="docutils literal"><span class="pre">array</span></tt> module). There isn’t a lot Django can do about that, since, again,
the information needed to make the necessary conversions isn’t available when
the data is read in from the database. This problem was <a class="reference external" href="http://sourceforge.net/tracker/index.php?func=detail&aid=1495765&group_id=22307&atid=374932">fixed in MySQLdb
1.2.2</a>, so if you want to use <a class="reference internal" href="models/fields.html#django.db.models.TextField" title="django.db.models.TextField"><tt class="xref py py-class docutils literal"><span class="pre">TextField</span></tt></a> with
<tt class="docutils literal"><span class="pre">utf8_bin</span></tt> collation, upgrading to version 1.2.2 and then dealing with the
bytestrings (which shouldn’t be too difficult) as described above is the
recommended solution.</p>
<p>Should you decide to use <tt class="docutils literal"><span class="pre">utf8_bin</span></tt> collation for some of your tables with
MySQLdb 1.2.1p2 or 1.2.2, you should still use <tt class="docutils literal"><span class="pre">utf8_collation_ci_swedish</span></tt>
(the default) collation for the <tt class="xref py py-class docutils literal"><span class="pre">django.contrib.sessions.models.Session</span></tt>
table (usually called <tt class="docutils literal"><span class="pre">django_session</span></tt>) and the
<tt class="xref py py-class docutils literal"><span class="pre">django.contrib.admin.models.LogEntry</span></tt> table (usually called
<tt class="docutils literal"><span class="pre">django_admin_log</span></tt>). Those are the two standard tables that use
<a class="reference internal" href="models/fields.html#django.db.models.TextField" title="django.db.models.TextField"><tt class="xref py py-class docutils literal"><span class="pre">TextField</span></tt></a> internally.</p>
</div>
</div>
<div class="section" id="s-connecting-to-the-database">
<span id="connecting-to-the-database"></span><h3>Connecting to the database<a class="headerlink" href="#connecting-to-the-database" title="Permalink to this headline">¶</a></h3>
<p>Refer to the <a class="reference internal" href="settings.html"><em>settings documentation</em></a>.</p>
<p>Connection settings are used in this order:</p>
<ol class="arabic simple">
<li><a class="reference internal" href="settings.html#std:setting-OPTIONS"><tt class="xref std std-setting docutils literal"><span class="pre">OPTIONS</span></tt></a>.</li>
<li><a class="reference internal" href="settings.html#std:setting-NAME"><tt class="xref std std-setting docutils literal"><span class="pre">NAME</span></tt></a>, <a class="reference internal" href="settings.html#std:setting-USER"><tt class="xref std std-setting docutils literal"><span class="pre">USER</span></tt></a>, <a class="reference internal" href="settings.html#std:setting-PASSWORD"><tt class="xref std std-setting docutils literal"><span class="pre">PASSWORD</span></tt></a>,
<a class="reference internal" href="settings.html#std:setting-HOST"><tt class="xref std std-setting docutils literal"><span class="pre">HOST</span></tt></a>, <a class="reference internal" href="settings.html#std:setting-PORT"><tt class="xref std std-setting docutils literal"><span class="pre">PORT</span></tt></a></li>
<li>MySQL option files.</li>
</ol>
<p>In other words, if you set the name of the database in <a class="reference internal" href="settings.html#std:setting-OPTIONS"><tt class="xref std std-setting docutils literal"><span class="pre">OPTIONS</span></tt></a>,
this will take precedence over <a class="reference internal" href="settings.html#std:setting-NAME"><tt class="xref std std-setting docutils literal"><span class="pre">NAME</span></tt></a>, which would override
anything in a <a class="reference external" href="http://dev.mysql.com/doc/refman/5.0/en/option-files.html">MySQL option file</a>.</p>
<p>Here’s a sample configuration which uses a MySQL option file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># settings.py</span>
<span class="n">DATABASES</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'default'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'ENGINE'</span><span class="p">:</span> <span class="s">'django.db.backends.mysql'</span><span class="p">,</span>
<span class="s">'OPTIONS'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'read_default_file'</span><span class="p">:</span> <span class="s">'/path/to/my.cnf'</span><span class="p">,</span>
<span class="p">},</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="c"># my.cnf</span>
<span class="p">[</span><span class="n">client</span><span class="p">]</span>
<span class="n">database</span> <span class="o">=</span> <span class="n">NAME</span>
<span class="n">user</span> <span class="o">=</span> <span class="n">USER</span>
<span class="n">password</span> <span class="o">=</span> <span class="n">PASSWORD</span>
<span class="n">default</span><span class="o">-</span><span class="n">character</span><span class="o">-</span><span class="nb">set</span> <span class="o">=</span> <span class="n">utf8</span>
</pre></div>
</div>
<p>Several other MySQLdb connection options may be useful, such as <tt class="docutils literal"><span class="pre">ssl</span></tt>,
<tt class="docutils literal"><span class="pre">use_unicode</span></tt>, <tt class="docutils literal"><span class="pre">init_command</span></tt>, and <tt class="docutils literal"><span class="pre">sql_mode</span></tt>. Consult the
<a class="reference external" href="http://mysql-python.sourceforge.net/">MySQLdb documentation</a> for more details.</p>
</div>
<div class="section" id="s-creating-your-tables">
<span id="creating-your-tables"></span><h3>Creating your tables<a class="headerlink" href="#creating-your-tables" title="Permalink to this headline">¶</a></h3>
<p>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.</p>
<p>If you’re using a hosting service and can’t change your server’s default
storage engine, you have a couple of options.</p>
<ul>
<li><p class="first">After the tables are created, execute an <tt class="docutils literal"><span class="pre">ALTER</span> <span class="pre">TABLE</span></tt> statement to
convert a table to a new storage engine (such as InnoDB):</p>
<div class="highlight-python"><pre>ALTER TABLE <tablename> ENGINE=INNODB;</pre>
</div>
<p>This can be tedious if you have a lot of tables.</p>
</li>
<li><p class="first">Another option is to use the <tt class="docutils literal"><span class="pre">init_command</span></tt> option for MySQLdb prior to
creating your tables:</p>
<div class="highlight-python"><pre>'OPTIONS': {
'init_command': 'SET storage_engine=INNODB',
}</pre>
</div>
<p>This sets the default storage engine upon connecting to the database.
After your tables have been created, you should remove this option as it
adds a query that is only needed during table creation to each database
connection.</p>
</li>
<li><p class="first">Another method for changing the storage engine is described in
<a class="reference external" href="https://code.djangoproject.com/wiki/AlterModelOnSyncDB">AlterModelOnSyncDB</a>.</p>
</li>
</ul>
</div>
<div class="section" id="s-table-names">
<span id="table-names"></span><h3>Table names<a class="headerlink" href="#table-names" title="Permalink to this headline">¶</a></h3>
<p>There are <a class="reference external" href="http://bugs.mysql.com/bug.php?id=48875">known issues</a> in even the latest versions of MySQL that can cause the
case of a table name to be altered when certain SQL statements are executed
under certain conditions. It is recommended that you use lowercase table
names, if possible, to avoid any problems that might arise from this behavior.
Django uses lowercase table names when it auto-generates table names from
models, so this is mainly a consideration if you are overriding the table name
via the <a class="reference internal" href="models/options.html#django.db.models.Options.db_table" title="django.db.models.Options.db_table"><tt class="xref py py-class docutils literal"><span class="pre">db_table</span></tt></a> parameter.</p>
</div>
<div class="section" id="s-savepoints">
<span id="savepoints"></span><h3>Savepoints<a class="headerlink" href="#savepoints" title="Permalink to this headline">¶</a></h3>
<p>Both the Django ORM and MySQL (when using the InnoDB <a class="reference internal" href="#mysql-storage-engines"><em>storage engine</em></a>) support database <a class="reference internal" href="../topics/db/transactions.html#topics-db-transactions-savepoints"><em>savepoints</em></a>, but this feature wasn’t available in
Django until version 1.4 when such supports was added.</p>
<p>If you use the MyISAM storage engine please be aware of the fact that you will
receive database-generated errors if you try to use the <a class="reference internal" href="../topics/db/transactions.html#topics-db-transactions-savepoints"><em>savepoint-related
methods of the transactions API</em></a>. The reason
for this is that detecting the storage engine of a MySQL database/table is an
expensive operation so it was decided it isn’t worth to dynamically convert
these methods in no-op’s based in the results of such detection.</p>
</div>
<div class="section" id="s-notes-on-specific-fields">
<span id="notes-on-specific-fields"></span><h3>Notes on specific fields<a class="headerlink" href="#notes-on-specific-fields" title="Permalink to this headline">¶</a></h3>
<div class="section" id="s-boolean-fields">
<span id="boolean-fields"></span><h4>Boolean fields<a class="headerlink" href="#boolean-fields" title="Permalink to this headline">¶</a></h4>
<div class="versionchanged">
<span class="title">Changed in Django 1.2:</span> <a class="reference internal" href="../releases/1.2.html"><em>Please see the release notes</em></a></div>
<p>In previous versions of Django when running under MySQL <tt class="docutils literal"><span class="pre">BooleanFields</span></tt> would
return their data as <tt class="docutils literal"><span class="pre">ints</span></tt>, instead of true <tt class="docutils literal"><span class="pre">bools</span></tt>. See the release
notes for a complete description of the change.</p>
</div>
<div class="section" id="s-character-fields">
<span id="character-fields"></span><h4>Character fields<a class="headerlink" href="#character-fields" title="Permalink to this headline">¶</a></h4>
<p>Any fields that are stored with <tt class="docutils literal"><span class="pre">VARCHAR</span></tt> column types have their
<tt class="docutils literal"><span class="pre">max_length</span></tt> restricted to 255 characters if you are using <tt class="docutils literal"><span class="pre">unique=True</span></tt>
for the field. This affects <a class="reference internal" href="models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><tt class="xref py py-class docutils literal"><span class="pre">CharField</span></tt></a>,
<a class="reference internal" href="models/fields.html#django.db.models.SlugField" title="django.db.models.SlugField"><tt class="xref py py-class docutils literal"><span class="pre">SlugField</span></tt></a> and
<a class="reference internal" href="models/fields.html#django.db.models.CommaSeparatedIntegerField" title="django.db.models.CommaSeparatedIntegerField"><tt class="xref py py-class docutils literal"><span class="pre">CommaSeparatedIntegerField</span></tt></a>.</p>
<p>Furthermore, if you are using a version of MySQL prior to 5.0.3, all of those
column types have a maximum length restriction of 255 characters, regardless
of whether <tt class="docutils literal"><span class="pre">unique=True</span></tt> is specified or not.</p>
</div>
<div class="section" id="s-datetime-fields">
<span id="datetime-fields"></span><h4>DateTime fields<a class="headerlink" href="#datetime-fields" title="Permalink to this headline">¶</a></h4>
<p>MySQL does not have a timezone-aware column type. If an attempt is made to
store a timezone-aware <tt class="docutils literal"><span class="pre">time</span></tt> or <tt class="docutils literal"><span class="pre">datetime</span></tt> to a
<a class="reference internal" href="models/fields.html#django.db.models.TimeField" title="django.db.models.TimeField"><tt class="xref py py-class docutils literal"><span class="pre">TimeField</span></tt></a> or <a class="reference internal" href="models/fields.html#django.db.models.DateTimeField" title="django.db.models.DateTimeField"><tt class="xref py py-class docutils literal"><span class="pre">DateTimeField</span></tt></a>
respectively, a <tt class="docutils literal"><span class="pre">ValueError</span></tt> is raised rather than truncating data.</p>
<p>MySQL does not store fractions of seconds. Fractions of seconds are truncated
to zero when the time is stored.</p>
</div>
</div>
<div class="section" id="s-row-locking-with-queryset-select-for-update">
<span id="row-locking-with-queryset-select-for-update"></span><h3>Row locking with <tt class="docutils literal"><span class="pre">QuerySet.select_for_update()</span></tt><a class="headerlink" href="#row-locking-with-queryset-select-for-update" title="Permalink to this headline">¶</a></h3>
<p>MySQL does not support the <tt class="docutils literal"><span class="pre">NOWAIT</span></tt> option to the <tt class="docutils literal"><span class="pre">SELECT</span> <span class="pre">...</span> <span class="pre">FOR</span> <span class="pre">UPDATE</span></tt>
statement. If <tt class="docutils literal"><span class="pre">select_for_update()</span></tt> is used with <tt class="docutils literal"><span class="pre">nowait=True</span></tt> then a
<tt class="docutils literal"><span class="pre">DatabaseError</span></tt> will be raised.</p>
</div>
</div>
<div class="section" id="s-sqlite-notes">
<span id="s-id9"></span><span id="sqlite-notes"></span><span id="id9"></span><h2>SQLite notes<a class="headerlink" href="#sqlite-notes" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="http://www.sqlite.org/">SQLite</a> provides an excellent development alternative for applications that
are predominantly read-only or require a smaller installation footprint. As
with all database servers, though, there are some differences that are
specific to SQLite that you should be aware of.</p>
<div class="section" id="s-substring-matching-and-case-sensitivity">
<span id="s-sqlite-string-matching"></span><span id="substring-matching-and-case-sensitivity"></span><span id="sqlite-string-matching"></span><h3>Substring matching and case sensitivity<a class="headerlink" href="#substring-matching-and-case-sensitivity" title="Permalink to this headline">¶</a></h3>
<p>For all SQLite versions, there is some slightly counter-intuitive behavior when
attempting to match some types of strings. These are triggered when using the
<a class="reference internal" href="models/querysets.html#std:fieldlookup-iexact"><tt class="xref std std-lookup docutils literal"><span class="pre">iexact</span></tt></a> or <a class="reference internal" href="models/querysets.html#std:fieldlookup-contains"><tt class="xref std std-lookup docutils literal"><span class="pre">contains</span></tt></a> filters in Querysets. The behavior
splits into two cases:</p>
<p>1. For substring matching, all matches are done case-insensitively. That is a
filter such as <tt class="docutils literal"><span class="pre">filter(name__contains="aa")</span></tt> will match a name of <tt class="docutils literal"><span class="pre">"Aabb"</span></tt>.</p>
<p>2. For strings containing characters outside the ASCII range, all exact string
matches are performed case-sensitively, even when the case-insensitive options
are passed into the query. So the <a class="reference internal" href="models/querysets.html#std:fieldlookup-iexact"><tt class="xref std std-lookup docutils literal"><span class="pre">iexact</span></tt></a> filter will behave exactly
the same as the <a class="reference internal" href="models/querysets.html#std:fieldlookup-exact"><tt class="xref std std-lookup docutils literal"><span class="pre">exact</span></tt></a> filter in these cases.</p>
<p>Some possible workarounds for this are <a class="reference external" href="http://www.sqlite.org/faq.html#q18">documented at sqlite.org</a>, but they
aren’t utilised by the default SQLite backend in Django, as incorporating them
would be fairly difficult to do robustly. Thus, Django exposes the default
SQLite behavior and you should be aware of this when doing case-insensitive or
substring filtering.</p>
</div>
<div class="section" id="s-sqlite-3-3-6-or-newer-strongly-recommended">
<span id="sqlite-3-3-6-or-newer-strongly-recommended"></span><h3>SQLite 3.3.6 or newer strongly recommended<a class="headerlink" href="#sqlite-3-3-6-or-newer-strongly-recommended" title="Permalink to this headline">¶</a></h3>
<p>Versions of SQLite 3.3.5 and older contains the following bugs:</p>
<ul class="simple">
<li>A bug when <a class="reference external" href="http://www.sqlite.org/cvstrac/tktview?tn=1768">handling</a> <tt class="docutils literal"><span class="pre">ORDER</span> <span class="pre">BY</span></tt> parameters. This can cause problems when
you use the <tt class="docutils literal"><span class="pre">select</span></tt> parameter for the <tt class="docutils literal"><span class="pre">extra()</span></tt> QuerySet method. The bug
can be identified by the error message <tt class="docutils literal"><span class="pre">OperationalError:</span> <span class="pre">ORDER</span> <span class="pre">BY</span> <span class="pre">terms</span>
<span class="pre">must</span> <span class="pre">not</span> <span class="pre">be</span> <span class="pre">non-integer</span> <span class="pre">constants</span></tt>.</li>
<li>A bug when handling <a class="reference external" href="https://code.djangoproject.com/ticket/10031">aggregation</a> together with DateFields and
DecimalFields.</li>
</ul>
<p>SQLite 3.3.6 was released in April 2006, so most current binary distributions
for different platforms include newer version of SQLite usable from Python
through either the <tt class="docutils literal"><span class="pre">pysqlite2</span></tt> or the <tt class="docutils literal"><span class="pre">sqlite3</span></tt> modules.</p>
<p>However, some platform/Python version combinations include older versions of
SQLite (e.g. the official binary distribution of Python 2.5 for Windows, 2.5.4
as of this writing, includes SQLite 3.3.4). There are (as of Django 1.1) even
some tests in the Django test suite that will fail when run under this setup.</p>
<p>As described <a class="reference internal" href="#using-newer-versions-of-pysqlite"><em>below</em></a>, this can be solved
by downloading and installing a newer version of <tt class="docutils literal"><span class="pre">pysqlite2</span></tt>
(<tt class="docutils literal"><span class="pre">pysqlite-2.x.x.win32-py2.5.exe</span></tt> in the described case) that includes and
uses a newer version of SQLite. Python 2.6 for Windows ships with a version of
SQLite that is not affected by these issues.</p>
</div>
<div class="section" id="s-version-3-5-9">
<span id="version-3-5-9"></span><h3>Version 3.5.9<a class="headerlink" href="#version-3-5-9" title="Permalink to this headline">¶</a></h3>
<p>The Ubuntu “Intrepid Ibex” (8.10) SQLite 3.5.9-3 package contains a bug that
causes problems with the evaluation of query expressions. If you are using
Ubuntu “Intrepid Ibex”, you will need to update the package to version
3.5.9-3ubuntu1 or newer (recommended) or find an alternate source for SQLite
packages, or install SQLite from source.</p>
<p>At one time, Debian Lenny shipped with the same malfunctioning SQLite 3.5.9-3
package. However the Debian project has subsequently issued updated versions
of the SQLite package that correct these bugs. If you find you are getting
unexpected results under Debian, ensure you have updated your SQLite package
to 3.5.9-5 or later.</p>
<p>The problem does not appear to exist with other versions of SQLite packaged
with other operating systems.</p>
</div>
<div class="section" id="s-version-3-6-2">
<span id="version-3-6-2"></span><h3>Version 3.6.2<a class="headerlink" href="#version-3-6-2" title="Permalink to this headline">¶</a></h3>
<p>SQLite version 3.6.2 (released August 30, 2008) introduced a bug into <tt class="docutils literal"><span class="pre">SELECT</span>
<span class="pre">DISTINCT</span></tt> handling that is triggered by, amongst other things, Django’s
<tt class="docutils literal"><span class="pre">DateQuerySet</span></tt> (returned by the <tt class="docutils literal"><span class="pre">dates()</span></tt> method on a queryset).</p>
<p>You should avoid using this version of SQLite with Django. Either upgrade to
3.6.3 (released September 22, 2008) or later, or downgrade to an earlier
version of SQLite.</p>
</div>
<div class="section" id="s-using-newer-versions-of-the-sqlite-db-api-2-0-driver">
<span id="s-using-newer-versions-of-pysqlite"></span><span id="using-newer-versions-of-the-sqlite-db-api-2-0-driver"></span><span id="using-newer-versions-of-pysqlite"></span><h3>Using newer versions of the SQLite DB-API 2.0 driver<a class="headerlink" href="#using-newer-versions-of-the-sqlite-db-api-2-0-driver" title="Permalink to this headline">¶</a></h3>
<p>For versions of Python 2.5 or newer that include <tt class="docutils literal"><span class="pre">sqlite3</span></tt> in the standard
library Django will now use a <tt class="docutils literal"><span class="pre">pysqlite2</span></tt> interface in preference to
<tt class="docutils literal"><span class="pre">sqlite3</span></tt> if it finds one is available.</p>
<p>This provides the ability to upgrade both the DB-API 2.0 interface or SQLite 3
itself to versions newer than the ones included with your particular Python
binary distribution, if needed.</p>
</div>
<div class="section" id="s-database-is-locked-errors">
<span id="database-is-locked-errors"></span><h3>“Database is locked” errors<a class="headerlink" href="#database-is-locked-errors" title="Permalink to this headline">¶</a></h3>
<p>SQLite is meant to be a lightweight database, and thus can’t support a high
level of concurrency. <tt class="docutils literal"><span class="pre">OperationalError:</span> <span class="pre">database</span> <span class="pre">is</span> <span class="pre">locked</span></tt> errors indicate
that your application is experiencing more concurrency than <tt class="docutils literal"><span class="pre">sqlite</span></tt> can
handle in default configuration. This error means that one thread or process has
an exclusive lock on the database connection and another thread timed out
waiting for the lock the be released.</p>
<p>Python’s SQLite wrapper has
a default timeout value that determines how long the second thread is allowed to
wait on the lock before it times out and raises the <tt class="docutils literal"><span class="pre">OperationalError:</span> <span class="pre">database</span>
<span class="pre">is</span> <span class="pre">locked</span></tt> error.</p>
<p>If you’re getting this error, you can solve it by:</p>
<ul>
<li><p class="first">Switching to another database backend. At a certain point SQLite becomes
too “lite” for real-world applications, and these sorts of concurrency
errors indicate you’ve reached that point.</p>
</li>
<li><p class="first">Rewriting your code to reduce concurrency and ensure that database
transactions are short-lived.</p>
</li>
<li><p class="first">Increase the default timeout value by setting the <tt class="docutils literal"><span class="pre">timeout</span></tt> database
option option:</p>
<div class="highlight-python"><pre>'OPTIONS': {
# ...
'timeout': 20,
# ...
}</pre>
</div>
<p>This will simply make SQLite wait a bit longer before throwing “database
is locked” errors; it won’t really do anything to solve them.</p>
</li>
</ul>
</div>
<div class="section" id="s-queryset-select-for-update-not-supported">
<span id="queryset-select-for-update-not-supported"></span><h3><tt class="docutils literal"><span class="pre">QuerySet.select_for_update()</span></tt> not supported<a class="headerlink" href="#queryset-select-for-update-not-supported" title="Permalink to this headline">¶</a></h3>
<p>SQLite does not support the <tt class="docutils literal"><span class="pre">SELECT</span> <span class="pre">...</span> <span class="pre">FOR</span> <span class="pre">UPDATE</span></tt> syntax. Calling it will
have no effect.</p>
</div>
<div class="section" id="s-parameters-not-quoted-in-connection-queries">
<span id="s-sqlite-connection-queries"></span><span id="parameters-not-quoted-in-connection-queries"></span><span id="sqlite-connection-queries"></span><h3>Parameters not quoted in <tt class="docutils literal"><span class="pre">connection.queries</span></tt><a class="headerlink" href="#parameters-not-quoted-in-connection-queries" title="Permalink to this headline">¶</a></h3>
<p><tt class="docutils literal"><span class="pre">sqlite3</span></tt> does not provide a way to retrieve the SQL after quoting and
substituting the parameters. Instead, the SQL in <tt class="docutils literal"><span class="pre">connection.queries</span></tt> is
rebuilt with a simple string interpolation. It may be incorrect. Make sure
you add quotes where necessary before copying a query into a SQLite shell.</p>
</div>
</div>
<div class="section" id="s-oracle-notes">
<span id="s-id10"></span><span id="oracle-notes"></span><span id="id10"></span><h2>Oracle notes<a class="headerlink" href="#oracle-notes" title="Permalink to this headline">¶</a></h2>
<p>Django supports <a class="reference external" href="http://www.oracle.com/">Oracle Database Server</a> versions 9i and
higher. Oracle version 10g or later is required to use Django’s
<tt class="docutils literal"><span class="pre">regex</span></tt> and <tt class="docutils literal"><span class="pre">iregex</span></tt> query operators. You will also need at least
version 4.3.1 of the <a class="reference external" href="http://cx-oracle.sourceforge.net/">cx_Oracle</a> Python driver.</p>
<p>Note that due to a Unicode-corruption bug in <tt class="docutils literal"><span class="pre">cx_Oracle</span></tt> 5.0, that
version of the driver should <strong>not</strong> be used with Django;
<tt class="docutils literal"><span class="pre">cx_Oracle</span></tt> 5.0.1 resolved this issue, so if you’d like to use a
more recent <tt class="docutils literal"><span class="pre">cx_Oracle</span></tt>, use version 5.0.1.</p>
<p><tt class="docutils literal"><span class="pre">cx_Oracle</span></tt> 5.0.1 or greater can optionally be compiled with the
<tt class="docutils literal"><span class="pre">WITH_UNICODE</span></tt> environment variable. This is recommended but not
required.</p>
<p>In order for the <tt class="docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">syncdb</span></tt> command to work, your Oracle
database user must have privileges to run the following commands:</p>
<ul class="simple">
<li>CREATE TABLE</li>
<li>CREATE SEQUENCE</li>
<li>CREATE PROCEDURE</li>
<li>CREATE TRIGGER</li>
</ul>
<p>To run Django’s test suite, the user needs these <em>additional</em> privileges:</p>
<ul class="simple">
<li>CREATE USER</li>
<li>DROP USER</li>
<li>CREATE TABLESPACE</li>
<li>DROP TABLESPACE</li>
<li>CONNECT WITH ADMIN OPTION</li>
<li>RESOURCE WITH ADMIN OPTION</li>
</ul>
<div class="section" id="s-id11">
<span id="id11"></span><h3>Connecting to the database<a class="headerlink" href="#id11" title="Permalink to this headline">¶</a></h3>
<p>Your Django settings.py file should look something like this for Oracle:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">DATABASES</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'default'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'ENGINE'</span><span class="p">:</span> <span class="s">'django.db.backends.oracle'</span><span class="p">,</span>
<span class="s">'NAME'</span><span class="p">:</span> <span class="s">'xe'</span><span class="p">,</span>
<span class="s">'USER'</span><span class="p">:</span> <span class="s">'a_user'</span><span class="p">,</span>
<span class="s">'PASSWORD'</span><span class="p">:</span> <span class="s">'a_password'</span><span class="p">,</span>
<span class="s">'HOST'</span><span class="p">:</span> <span class="s">''</span><span class="p">,</span>
<span class="s">'PORT'</span><span class="p">:</span> <span class="s">''</span><span class="p">,</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<p>If you don’t use a <tt class="docutils literal"><span class="pre">tnsnames.ora</span></tt> file or a similar naming method that
recognizes the SID (“xe” in this example), then fill in both
<a class="reference internal" href="settings.html#std:setting-HOST"><tt class="xref std std-setting docutils literal"><span class="pre">HOST</span></tt></a> and <a class="reference internal" href="settings.html#std:setting-PORT"><tt class="xref std std-setting docutils literal"><span class="pre">PORT</span></tt></a> like so:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">DATABASES</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'default'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'ENGINE'</span><span class="p">:</span> <span class="s">'django.db.backends.oracle'</span><span class="p">,</span>
<span class="s">'NAME'</span><span class="p">:</span> <span class="s">'xe'</span><span class="p">,</span>
<span class="s">'USER'</span><span class="p">:</span> <span class="s">'a_user'</span><span class="p">,</span>
<span class="s">'PASSWORD'</span><span class="p">:</span> <span class="s">'a_password'</span><span class="p">,</span>
<span class="s">'HOST'</span><span class="p">:</span> <span class="s">'dbprod01ned.mycompany.com'</span><span class="p">,</span>
<span class="s">'PORT'</span><span class="p">:</span> <span class="s">'1540'</span><span class="p">,</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<p>You should supply both <a class="reference internal" href="settings.html#std:setting-HOST"><tt class="xref std std-setting docutils literal"><span class="pre">HOST</span></tt></a> and <a class="reference internal" href="settings.html#std:setting-PORT"><tt class="xref std std-setting docutils literal"><span class="pre">PORT</span></tt></a>, or leave both
as empty strings.</p>
</div>
<div class="section" id="s-threaded-option">
<span id="threaded-option"></span><h3>Threaded option<a class="headerlink" href="#threaded-option" title="Permalink to this headline">¶</a></h3>
<p>If you plan to run Django in a multithreaded environment (e.g. Apache in Windows
using the default MPM module), then you <strong>must</strong> set the <tt class="docutils literal"><span class="pre">threaded</span></tt> option of
your Oracle database configuration to True:</p>
<div class="highlight-python"><pre>'OPTIONS': {
'threaded': True,
},</pre>
</div>
<p>Failure to do this may result in crashes and other odd behavior.</p>
</div>
<div class="section" id="s-insert-returning-into">
<span id="insert-returning-into"></span><h3>INSERT ... RETURNING INTO<a class="headerlink" href="#insert-returning-into" title="Permalink to this headline">¶</a></h3>
<p>By default, the Oracle backend uses a <tt class="docutils literal"><span class="pre">RETURNING</span> <span class="pre">INTO</span></tt> clause to efficiently
retrieve the value of an <tt class="docutils literal"><span class="pre">AutoField</span></tt> when inserting new rows. This behavior
may result in a <tt class="docutils literal"><span class="pre">DatabaseError</span></tt> in certain unusual setups, such as when
inserting into a remote table, or into a view with an <tt class="docutils literal"><span class="pre">INSTEAD</span> <span class="pre">OF</span></tt> trigger.
The <tt class="docutils literal"><span class="pre">RETURNING</span> <span class="pre">INTO</span></tt> clause can be disabled by setting the
<tt class="docutils literal"><span class="pre">use_returning_into</span></tt> option of the database configuration to False:</p>
<div class="highlight-python"><pre>'OPTIONS': {
'use_returning_into': False,
},</pre>
</div>
<p>In this case, the Oracle backend will use a separate <tt class="docutils literal"><span class="pre">SELECT</span></tt> query to
retrieve AutoField values.</p>
</div>
<div class="section" id="s-naming-issues">
<span id="naming-issues"></span><h3>Naming issues<a class="headerlink" href="#naming-issues" title="Permalink to this headline">¶</a></h3>
<p>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.</p>
<p>When running syncdb, an <tt class="docutils literal"><span class="pre">ORA-06552</span></tt> error may be encountered if
certain Oracle keywords are used as the name of a model field or the
value of a <tt class="docutils literal"><span class="pre">db_column</span></tt> option. Django quotes all identifiers used
in queries to prevent most such problems, but this error can still
occur when an Oracle datatype is used as a column name. In
particular, take care to avoid using the names <tt class="docutils literal"><span class="pre">date</span></tt>,
<tt class="docutils literal"><span class="pre">timestamp</span></tt>, <tt class="docutils literal"><span class="pre">number</span></tt> or <tt class="docutils literal"><span class="pre">float</span></tt> as a field name.</p>
</div>
<div class="section" id="s-null-and-empty-strings">
<span id="null-and-empty-strings"></span><h3>NULL and empty strings<a class="headerlink" href="#null-and-empty-strings" title="Permalink to this headline">¶</a></h3>
<p>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 <tt class="docutils literal"><span class="pre">null=True</span></tt> option on fields that have
the empty string as a possible 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.</p>
</div>
<div class="section" id="s-textfield-limitations">
<span id="textfield-limitations"></span><h3><tt class="docutils literal"><span class="pre">TextField</span></tt> limitations<a class="headerlink" href="#textfield-limitations" title="Permalink to this headline">¶</a></h3>
<p>The Oracle backend stores <tt class="docutils literal"><span class="pre">TextFields</span></tt> as <tt class="docutils literal"><span class="pre">NCLOB</span></tt> columns. Oracle imposes
some limitations on the usage of such LOB columns in general:</p>
<ul class="simple">
<li>LOB columns may not be used as primary keys.</li>
<li>LOB columns may not be used in indexes.</li>
<li>LOB columns may not be used in a <tt class="docutils literal"><span class="pre">SELECT</span> <span class="pre">DISTINCT</span></tt> list. This means that
attempting to use the <tt class="docutils literal"><span class="pre">QuerySet.distinct</span></tt> method on a model that
includes <tt class="docutils literal"><span class="pre">TextField</span></tt> columns will result in an error when run against
Oracle. As a workaround, use the <tt class="docutils literal"><span class="pre">QuerySet.defer</span></tt> method in conjunction
with <tt class="docutils literal"><span class="pre">distinct()</span></tt> to prevent <tt class="docutils literal"><span class="pre">TextField</span></tt> columns from being included in
the <tt class="docutils literal"><span class="pre">SELECT</span> <span class="pre">DISTINCT</span></tt> list.</li>
</ul>
</div>
</div>
<div class="section" id="s-using-a-3rd-party-database-backend">
<span id="s-third-party-notes"></span><span id="using-a-3rd-party-database-backend"></span><span id="third-party-notes"></span><h2>Using a 3rd-party database backend<a class="headerlink" href="#using-a-3rd-party-database-backend" title="Permalink to this headline">¶</a></h2>
<p>In addition to the officially supported databases, there are backends provided
by 3rd parties that allow you to use other databases with Django:</p>
<ul class="simple">
<li><a class="reference external" href="http://code.google.com/p/sqlany-django/">Sybase SQL Anywhere</a></li>
<li><a class="reference external" href="http://code.google.com/p/ibm-db/">IBM DB2</a></li>
<li><a class="reference external" href="http://code.google.com/p/django-mssql/">Microsoft SQL Server 2005</a></li>
<li><a class="reference external" href="http://code.google.com/p/django-firebird/">Firebird</a></li>
<li><a class="reference external" href="http://code.google.com/p/django-pyodbc/">ODBC</a></li>
<li><a class="reference external" href="http://code.google.com/p/adsdb-django/">ADSDB</a></li>
</ul>
<p>The Django versions and ORM features supported by these unofficial backends
vary considerably. Queries regarding the specific capabilities of these
unofficial backends, along with any support queries, should be directed to
the support channels provided by each 3rd party project.</p>
</div>
</div>
</div>
</div>
</div>
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<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Databases</a><ul>
<li><a class="reference internal" href="#postgresql-notes">PostgreSQL notes</a><ul>
<li><a class="reference internal" href="#postgresql-8-2-to-8-2-4">PostgreSQL 8.2 to 8.2.4</a></li>
<li><a class="reference internal" href="#optimizing-postgresql-s-configuration">Optimizing PostgreSQL’s configuration</a></li>
<li><a class="reference internal" href="#transaction-handling">Transaction handling</a><ul>
<li><a class="reference internal" href="#autocommit-mode">Autocommit mode</a></li>
<li><a class="reference internal" href="#indexes-for-varchar-and-text-columns">Indexes for <tt class="docutils literal"><span class="pre">varchar</span></tt> and <tt class="docutils literal"><span class="pre">text</span></tt> columns</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#mysql-notes">MySQL notes</a><ul>
<li><a class="reference internal" href="#mysql-4-1">MySQL 4.1</a></li>
<li><a class="reference internal" href="#mysql-5-0">MySQL 5.0</a></li>
<li><a class="reference internal" href="#storage-engines">Storage engines</a></li>
<li><a class="reference internal" href="#mysqldb">MySQLdb</a></li>
<li><a class="reference internal" href="#creating-your-database">Creating your database</a><ul>
<li><a class="reference internal" href="#collation-settings">Collation settings</a></li>
</ul>
</li>
<li><a class="reference internal" href="#connecting-to-the-database">Connecting to the database</a></li>
<li><a class="reference internal" href="#creating-your-tables">Creating your tables</a></li>
<li><a class="reference internal" href="#table-names">Table names</a></li>
<li><a class="reference internal" href="#savepoints">Savepoints</a></li>
<li><a class="reference internal" href="#notes-on-specific-fields">Notes on specific fields</a><ul>
<li><a class="reference internal" href="#boolean-fields">Boolean fields</a></li>
<li><a class="reference internal" href="#character-fields">Character fields</a></li>
<li><a class="reference internal" href="#datetime-fields">DateTime fields</a></li>
</ul>
</li>
<li><a class="reference internal" href="#row-locking-with-queryset-select-for-update">Row locking with <tt class="docutils literal"><span class="pre">QuerySet.select_for_update()</span></tt></a></li>
</ul>
</li>
<li><a class="reference internal" href="#sqlite-notes">SQLite notes</a><ul>
<li><a class="reference internal" href="#substring-matching-and-case-sensitivity">Substring matching and case sensitivity</a></li>
<li><a class="reference internal" href="#sqlite-3-3-6-or-newer-strongly-recommended">SQLite 3.3.6 or newer strongly recommended</a></li>
<li><a class="reference internal" href="#version-3-5-9">Version 3.5.9</a></li>
<li><a class="reference internal" href="#version-3-6-2">Version 3.6.2</a></li>
<li><a class="reference internal" href="#using-newer-versions-of-the-sqlite-db-api-2-0-driver">Using newer versions of the SQLite DB-API 2.0 driver</a></li>
<li><a class="reference internal" href="#database-is-locked-errors">“Database is locked” errors</a></li>
<li><a class="reference internal" href="#queryset-select-for-update-not-supported"><tt class="docutils literal"><span class="pre">QuerySet.select_for_update()</span></tt> not supported</a></li>
<li><a class="reference internal" href="#parameters-not-quoted-in-connection-queries">Parameters not quoted in <tt class="docutils literal"><span class="pre">connection.queries</span></tt></a></li>
</ul>
</li>
<li><a class="reference internal" href="#oracle-notes">Oracle notes</a><ul>
<li><a class="reference internal" href="#id11">Connecting to the database</a></li>
<li><a class="reference internal" href="#threaded-option">Threaded option</a></li>
<li><a class="reference internal" href="#insert-returning-into">INSERT ... RETURNING INTO</a></li>
<li><a class="reference internal" href="#naming-issues">Naming issues</a></li>
<li><a class="reference internal" href="#null-and-empty-strings">NULL and empty strings</a></li>
<li><a class="reference internal" href="#textfield-limitations"><tt class="docutils literal"><span class="pre">TextField</span></tt> limitations</a></li>
</ul>
</li>
<li><a class="reference internal" href="#using-a-3rd-party-database-backend">Using a 3rd-party database backend</a></li>
</ul>
</li>
</ul>
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