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<h1><a href="../index.html">Django v1.2 documentation</a></h1>
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<div class="section" id="s-faq-databases-and-models">
<span id="faq-databases-and-models"></span><h1>FAQ: Databases and models<a class="headerlink" href="#faq-databases-and-models" title="Permalink to this headline">¶</a></h1>
<div class="section" id="s-how-can-i-see-the-raw-sql-queries-django-is-running">
<span id="s-faq-see-raw-sql-queries"></span><span id="how-can-i-see-the-raw-sql-queries-django-is-running"></span><span id="faq-see-raw-sql-queries"></span><h2>How can I see the raw SQL queries Django is running?<a class="headerlink" href="#how-can-i-see-the-raw-sql-queries-django-is-running" title="Permalink to this headline">¶</a></h2>
<p>Make sure your Django <tt class="docutils literal"><span class="pre">DEBUG</span></tt> setting is set to <tt class="xref docutils literal"><span class="pre">True</span></tt>. Then, just do
this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">django.db</span> <span class="kn">import</span> <span class="n">connection</span>
<span class="gp">>>> </span><span class="n">connection</span><span class="o">.</span><span class="n">queries</span>
<span class="go">[{'sql': 'SELECT polls_polls.id,polls_polls.question,polls_polls.pub_date FROM polls_polls',</span>
<span class="go">'time': '0.002'}]</span>
</pre></div>
</div>
<p><tt class="docutils literal"><span class="pre">connection.queries</span></tt> is only available if <tt class="docutils literal"><span class="pre">DEBUG</span></tt> is <tt class="xref docutils literal"><span class="pre">True</span></tt>. It's a list
of dictionaries in order of query execution. Each dictionary has the following:</p>
<div class="highlight-python"><pre>``sql`` -- The raw SQL statement
``time`` -- How long the statement took to execute, in seconds.</pre>
</div>
<p><tt class="docutils literal"><span class="pre">connection.queries</span></tt> includes all SQL statements -- INSERTs, UPDATES,
SELECTs, etc. Each time your app hits the database, the query will be recorded.
Note that the raw SQL logged in <tt class="docutils literal"><span class="pre">connection.queries</span></tt> may not include
parameter quoting. Parameter quoting is performed by the database-specific
backend, and not all backends provide a way to retrieve the SQL after quoting.</p>
<div class="versionadded">
<span class="title">New in Django 1.2:</span> <a class="reference internal" href="../releases/1.2.html"><em>Please, see the release notes</em></a></div>
<p>If you are using <a class="reference internal" href="../topics/db/multi-db.html"><em>multiple databases</em></a>, you can use the
same interface on each member of the <tt class="docutils literal"><span class="pre">connections</span></tt> dictionary:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">django.db</span> <span class="kn">import</span> <span class="n">connections</span>
<span class="gp">>>> </span><span class="n">connections</span><span class="p">[</span><span class="s">'my_db_alias'</span><span class="p">]</span><span class="o">.</span><span class="n">queries</span>
</pre></div>
</div>
</div>
<div class="section" id="s-can-i-use-django-with-a-pre-existing-database">
<span id="can-i-use-django-with-a-pre-existing-database"></span><h2>Can I use Django with a pre-existing database?<a class="headerlink" href="#can-i-use-django-with-a-pre-existing-database" title="Permalink to this headline">¶</a></h2>
<p>Yes. See <a class="reference internal" href="../howto/legacy-databases.html"><em>Integrating with a legacy database</em></a>.</p>
</div>
<div class="section" id="s-if-i-make-changes-to-a-model-how-do-i-update-the-database">
<span id="if-i-make-changes-to-a-model-how-do-i-update-the-database"></span><h2>If I make changes to a model, how do I update the database?<a class="headerlink" href="#if-i-make-changes-to-a-model-how-do-i-update-the-database" title="Permalink to this headline">¶</a></h2>
<p>If you don't mind clearing data, your project's <tt class="docutils literal"><span class="pre">manage.py</span></tt> utility has an
option to reset the SQL for a particular application:</p>
<div class="highlight-python"><pre>manage.py reset appname</pre>
</div>
<p>This drops any tables associated with <tt class="docutils literal"><span class="pre">appname</span></tt> and recreates them.</p>
<p>If you do care about deleting data, you'll have to execute the <tt class="docutils literal"><span class="pre">ALTER</span> <span class="pre">TABLE</span></tt>
statements manually in your database. That's the way we've always done it,
because dealing with data is a very sensitive operation that we've wanted to
avoid automating. That said, there's some work being done to add partially
automated database-upgrade functionality.</p>
</div>
<div class="section" id="s-do-django-models-support-multiple-column-primary-keys">
<span id="do-django-models-support-multiple-column-primary-keys"></span><h2>Do Django models support multiple-column primary keys?<a class="headerlink" href="#do-django-models-support-multiple-column-primary-keys" title="Permalink to this headline">¶</a></h2>
<p>No. Only single-column primary keys are supported.</p>
<p>But this isn't an issue in practice, because there's nothing stopping you from
adding other constraints (using the <tt class="docutils literal"><span class="pre">unique_together</span></tt> model option or
creating the constraint directly in your database), and enforcing the
uniqueness at that level. Single-column primary keys are needed for things such
as the admin interface to work; e.g., you need a simple way of being able to
specify an object to edit or delete.</p>
</div>
<div class="section" id="s-how-do-i-add-database-specific-options-to-my-create-table-statements-such-as-specifying-myisam-as-the-table-type">
<span id="how-do-i-add-database-specific-options-to-my-create-table-statements-such-as-specifying-myisam-as-the-table-type"></span><h2>How do I add database-specific options to my CREATE TABLE statements, such as specifying MyISAM as the table type?<a class="headerlink" href="#how-do-i-add-database-specific-options-to-my-create-table-statements-such-as-specifying-myisam-as-the-table-type" title="Permalink to this headline">¶</a></h2>
<p>We try to avoid adding special cases in the Django code to accommodate all the
database-specific options such as table type, etc. If you'd like to use any of
these options, create an <a class="reference internal" href="../howto/initial-data.html#initial-sql"><em>SQL initial data file</em></a> that
contains <tt class="docutils literal"><span class="pre">ALTER</span> <span class="pre">TABLE</span></tt> statements that do what you want to do. The initial
data files are executed in your database after the <tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">TABLE</span></tt> statements.</p>
<p>For example, if you're using MySQL and want your tables to use the MyISAM table
type, create an initial data file and put something like this in it:</p>
<div class="highlight-python"><pre>ALTER TABLE myapp_mytable ENGINE=MyISAM;</pre>
</div>
<p>As explained in the <a class="reference internal" href="../howto/initial-data.html#initial-sql"><em>SQL initial data file</em></a> documentation,
this SQL file can contain arbitrary SQL, so you can make any sorts of changes
you need to make.</p>
</div>
<div class="section" id="s-why-is-django-leaking-memory">
<span id="why-is-django-leaking-memory"></span><h2>Why is Django leaking memory?<a class="headerlink" href="#why-is-django-leaking-memory" title="Permalink to this headline">¶</a></h2>
<p>Django isn't known to leak memory. If you find your Django processes are
allocating more and more memory, with no sign of releasing it, check to make
sure your <tt class="docutils literal"><span class="pre">DEBUG</span></tt> setting is set to <tt class="xref docutils literal"><span class="pre">False</span></tt>. If <tt class="docutils literal"><span class="pre">DEBUG</span></tt> is <tt class="xref docutils literal"><span class="pre">True</span></tt>, then
Django saves a copy of every SQL statement it has executed.</p>
<p>(The queries are saved in <tt class="docutils literal"><span class="pre">django.db.connection.queries</span></tt>. See
<a class="reference internal" href="#how-can-i-see-the-raw-sql-queries-django-is-running">How can I see the raw SQL queries Django is running?</a>.)</p>
<p>To fix the problem, set <tt class="docutils literal"><span class="pre">DEBUG</span></tt> to <tt class="xref docutils literal"><span class="pre">False</span></tt>.</p>
<p>If you need to clear the query list manually at any point in your functions,
just call <tt class="docutils literal"><span class="pre">reset_queries()</span></tt>, like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django</span> <span class="kn">import</span> <span class="n">db</span>
<span class="n">db</span><span class="o">.</span><span class="n">reset_queries</span><span class="p">()</span>
</pre></div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">FAQ: Databases and models</a><ul>
<li><a class="reference internal" href="#how-can-i-see-the-raw-sql-queries-django-is-running">How can I see the raw SQL queries Django is running?</a></li>
<li><a class="reference internal" href="#can-i-use-django-with-a-pre-existing-database">Can I use Django with a pre-existing database?</a></li>
<li><a class="reference internal" href="#if-i-make-changes-to-a-model-how-do-i-update-the-database">If I make changes to a model, how do I update the database?</a></li>
<li><a class="reference internal" href="#do-django-models-support-multiple-column-primary-keys">Do Django models support multiple-column primary keys?</a></li>
<li><a class="reference internal" href="#how-do-i-add-database-specific-options-to-my-create-table-statements-such-as-specifying-myisam-as-the-table-type">How do I add database-specific options to my CREATE TABLE statements, such as specifying MyISAM as the table type?</a></li>
<li><a class="reference internal" href="#why-is-django-leaking-memory">Why is Django leaking memory?</a></li>
</ul>
</li>
</ul>
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