<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title> SQLite — SQLAlchemy 0.6.8 Documentation</title> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="../_static/docs.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '0.6.8', COLLAPSE_MODINDEX: false, FILE_SUFFIX: '.html' }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/init.js"></script> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="SQLAlchemy 0.6.8 Documentation" href="../index.html" /> <link rel="up" title="Dialects" href="index.html" /> <link rel="next" title="Sybase" href="sybase.html" /> <link rel="prev" title="PostgreSQL" href="postgresql.html" /> </head> <body> <h1>SQLAlchemy 0.6.8 Documentation</h1> <div id="search"> Search: <form class="search" action="../search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Search" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <div class="versionheader"> Version: <span class="versionnum">0.6.8</span> Last Updated: 06/05/2011 13:10:26 </div> <div class="clearboth"></div> <div id="topnav"> <div id="pagecontrol"> <ul> <li>Prev: <a href="postgresql.html" title="previous chapter">PostgreSQL</a> </li> <li>Next: <a href="sybase.html" title="next chapter">Sybase</a> </li> <li> <a href="../contents.html">Table of Contents</a> | <a href="../genindex.html">Index</a> | <a href="../_sources/dialects/sqlite.txt">view source </li> </ul> </div> <div id="navbanner"> <a class="totoc" href="../index.html">SQLAlchemy 0.6.8 Documentation</a> » <a href="index.html" title="Dialects">Dialects</a> » SQLite <h2> SQLite </h2> <ul> <li><a class="reference internal" href="#">SQLite</a><ul> <li><a class="reference internal" href="#date-and-time-types">Date and Time Types</a></li> <li><a class="reference internal" href="#auto-incrementing-behavior">Auto Incrementing Behavior</a></li> <li><a class="reference internal" href="#transaction-isolation-level">Transaction Isolation Level</a></li> <li><a class="reference internal" href="#sqlite-data-types">SQLite Data Types</a></li> <li><a class="reference internal" href="#module-sqlalchemy.dialects.sqlite.pysqlite">Pysqlite</a><ul> <li><a class="reference internal" href="#driver">Driver</a></li> <li><a class="reference internal" href="#connect-strings">Connect Strings</a></li> <li><a class="reference internal" href="#compatibility-with-sqlite3-native-date-and-datetime-types">Compatibility with sqlite3 “native” date and datetime types</a></li> <li><a class="reference internal" href="#threading-behavior">Threading Behavior</a></li> <li><a class="reference internal" href="#unicode">Unicode</a></li> </ul> </li> </ul> </li> </ul> </div> <div class="clearboth"></div> </div> <div class="document"> <div class="body"> <div class="section" id="module-sqlalchemy.dialects.sqlite.base"> <span id="sqlite"></span><h1>SQLite<a class="headerlink" href="#module-sqlalchemy.dialects.sqlite.base" title="Permalink to this headline">¶</a></h1> <p>Support for the SQLite database.</p> <p>For information on connecting using a specific driver, see the documentation section regarding that driver.</p> <div class="section" id="date-and-time-types"> <h2>Date and Time Types<a class="headerlink" href="#date-and-time-types" title="Permalink to this headline">¶</a></h2> <p>SQLite does not have built-in DATE, TIME, or DATETIME types, and pysqlite does not provide out of the box functionality for translating values between Python <cite>datetime</cite> objects and a SQLite-supported format. SQLAlchemy’s own <a class="reference internal" href="../core/types.html#sqlalchemy.types.DateTime" title="sqlalchemy.types.DateTime"><tt class="xref py py-class docutils literal"><span class="pre">DateTime</span></tt></a> and related types provide date formatting and parsing functionality when SQlite is used. The implementation classes are <tt class="xref py py-class docutils literal"><span class="pre">DATETIME</span></tt>, <tt class="xref py py-class docutils literal"><span class="pre">DATE</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">TIME</span></tt>. These types represent dates and times as ISO formatted strings, which also nicely support ordering. There’s no reliance on typical “libc” internals for these functions so historical dates are fully supported.</p> </div> <div class="section" id="auto-incrementing-behavior"> <h2>Auto Incrementing Behavior<a class="headerlink" href="#auto-incrementing-behavior" title="Permalink to this headline">¶</a></h2> <p>Background on SQLite’s autoincrement is at: <a class="reference external" href="http://sqlite.org/autoinc.html">http://sqlite.org/autoinc.html</a></p> <p>Two things to note:</p> <ul class="simple"> <li>The AUTOINCREMENT keyword is <strong>not</strong> required for SQLite tables to generate primary key values automatically. AUTOINCREMENT only means that the algorithm used to generate ROWID values should be slightly different.</li> <li>SQLite does <strong>not</strong> generate primary key (i.e. ROWID) values, even for one column, if the table has a composite (i.e. multi-column) primary key. This is regardless of the AUTOINCREMENT keyword being present or not.</li> </ul> <p>To specifically render the AUTOINCREMENT keyword on the primary key column when rendering DDL, add the flag <tt class="docutils literal"><span class="pre">sqlite_autoincrement=True</span></tt> to the Table construct:</p> <div class="highlight-python"><div class="highlight"><pre><span class="n">Table</span><span class="p">(</span><span class="s">'sometable'</span><span class="p">,</span> <span class="n">metadata</span><span class="p">,</span> <span class="n">Column</span><span class="p">(</span><span class="s">'id'</span><span class="p">,</span> <span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="bp">True</span><span class="p">),</span> <span class="n">sqlite_autoincrement</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span></pre></div> </div> </div> <div class="section" id="transaction-isolation-level"> <h2>Transaction Isolation Level<a class="headerlink" href="#transaction-isolation-level" title="Permalink to this headline">¶</a></h2> <p><tt class="xref py py-func docutils literal"><span class="pre">create_engine()</span></tt> accepts an <tt class="docutils literal"><span class="pre">isolation_level</span></tt> parameter which results in the command <tt class="docutils literal"><span class="pre">PRAGMA</span> <span class="pre">read_uncommitted</span> <span class="pre"><level></span></tt> being invoked for every new connection. Valid values for this parameter are <tt class="docutils literal"><span class="pre">SERIALIZABLE</span></tt> and <tt class="docutils literal"><span class="pre">READ</span> <span class="pre">UNCOMMITTED</span></tt> corresponding to a value of 0 and 1, respectively.</p> </div> <div class="section" id="sqlite-data-types"> <h2>SQLite Data Types<a class="headerlink" href="#sqlite-data-types" title="Permalink to this headline">¶</a></h2> <p>As with all SQLAlchemy dialects, all UPPERCASE types that are known to be valid with SQLite are importable from the top level dialect, whether they originate from <a class="reference internal" href="../core/types.html#module-sqlalchemy.types" title="sqlalchemy.types"><tt class="xref py py-mod docutils literal"><span class="pre">sqlalchemy.types</span></tt></a> or from the local dialect:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlalchemy.dialects.sqlite</span> <span class="kn">import</span> \ <span class="n">BLOB</span><span class="p">,</span> <span class="n">BOOLEAN</span><span class="p">,</span> <span class="n">CHAR</span><span class="p">,</span> <span class="n">DATE</span><span class="p">,</span> <span class="n">DATETIME</span><span class="p">,</span> <span class="n">DECIMAL</span><span class="p">,</span> <span class="n">FLOAT</span><span class="p">,</span> \ <span class="n">INTEGER</span><span class="p">,</span> <span class="n">NUMERIC</span><span class="p">,</span> <span class="n">SMALLINT</span><span class="p">,</span> <span class="n">TEXT</span><span class="p">,</span> <span class="n">TIME</span><span class="p">,</span> <span class="n">TIMESTAMP</span><span class="p">,</span> \ <span class="n">VARCHAR</span></pre></div> </div> <span class="target" id="module-sqlalchemy.dialects.sqlite"></span><dl class="class"> <dt id="sqlalchemy.dialects.sqlite.DATETIME"> <em class="property">class </em><tt class="descclassname">sqlalchemy.dialects.sqlite.</tt><tt class="descname">DATETIME</tt><big>(</big><em>storage_format=None</em>, <em>regexp=None</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#sqlalchemy.dialects.sqlite.DATETIME" title="Permalink to this definition">¶</a></dt> <dd><p>Represent a Python datetime object in SQLite using a string.</p> <p>The default string storage format is:</p> <div class="highlight-python"><div class="highlight"><pre><span class="s">"</span><span class="si">%04d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s"> </span><span class="si">%02d</span><span class="s">:</span><span class="si">%02d</span><span class="s">:</span><span class="si">%02d</span><span class="s">.</span><span class="si">%06d</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">value</span><span class="o">.</span><span class="n">year</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">month</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">day</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">hour</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">minute</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">second</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">microsecond</span><span class="p">)</span></pre></div> </div> <p>e.g.:</p> <div class="highlight-python"><pre>2011-03-15 12:05:57.10558</pre> </div> <p>The storage format can be customized to some degree using the <tt class="docutils literal"><span class="pre">storage_format</span></tt> and <tt class="docutils literal"><span class="pre">regexp</span></tt> parameters, such as:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">re</span> <span class="kn">from</span> <span class="nn">sqlalchemy.dialects.sqlite</span> <span class="kn">import</span> <span class="n">DATETIME</span> <span class="n">dt</span> <span class="o">=</span> <span class="n">DATETIME</span><span class="p">(</span> <span class="n">storage_format</span><span class="o">=</span><span class="s">"</span><span class="si">%04d</span><span class="s">/</span><span class="si">%02d</span><span class="s">/</span><span class="si">%02d</span><span class="s"> </span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%06d</span><span class="s">"</span><span class="p">,</span> <span class="n">regexp</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s">"(\d+)/(\d+)/(\d+) (\d+)-(\d+)-(\d+)(?:-(\d+))?"</span><span class="p">)</span> <span class="p">)</span></pre></div> </div> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple"> <li><strong>storage_format</strong> – format string which will be appled to the tuple <tt class="docutils literal"><span class="pre">(value.year,</span> <span class="pre">value.month,</span> <span class="pre">value.day,</span> <span class="pre">value.hour,</span> <span class="pre">value.minute,</span> <span class="pre">value.second,</span> <span class="pre">value.microsecond)</span></tt>, given a Python datetime.datetime() object.</li> <li><strong>regexp</strong> – regular expression which will be applied to incoming result rows. The resulting match object is appled to the Python datetime() constructor via <tt class="docutils literal"><span class="pre">*map(int,</span> <span class="pre">match_obj.groups(0))</span></tt>.</li> </ul> </td> </tr> </tbody> </table> </dd></dl> <dl class="class"> <dt id="sqlalchemy.dialects.sqlite.DATE"> <em class="property">class </em><tt class="descclassname">sqlalchemy.dialects.sqlite.</tt><tt class="descname">DATE</tt><big>(</big><em>storage_format=None</em>, <em>regexp=None</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#sqlalchemy.dialects.sqlite.DATE" title="Permalink to this definition">¶</a></dt> <dd><p>Represent a Python date object in SQLite using a string.</p> <p>The default string storage format is:</p> <div class="highlight-python"><div class="highlight"><pre><span class="s">"</span><span class="si">%04d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">value</span><span class="o">.</span><span class="n">year</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">month</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">day</span><span class="p">)</span></pre></div> </div> <p>e.g.:</p> <div class="highlight-python"><div class="highlight"><pre><span class="mi">2011</span><span class="o">-</span><span class="mo">03</span><span class="o">-</span><span class="mi">15</span></pre></div> </div> <p>The storage format can be customized to some degree using the <tt class="docutils literal"><span class="pre">storage_format</span></tt> and <tt class="docutils literal"><span class="pre">regexp</span></tt> parameters, such as:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">re</span> <span class="kn">from</span> <span class="nn">sqlalchemy.dialects.sqlite</span> <span class="kn">import</span> <span class="n">DATE</span> <span class="n">d</span> <span class="o">=</span> <span class="n">DATE</span><span class="p">(</span> <span class="n">storage_format</span><span class="o">=</span><span class="s">"</span><span class="si">%02d</span><span class="s">/</span><span class="si">%02d</span><span class="s">/</span><span class="si">%02d</span><span class="s">"</span><span class="p">,</span> <span class="n">regexp</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s">"(\d+)/(\d+)/(\d+)"</span><span class="p">)</span> <span class="p">)</span></pre></div> </div> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple"> <li><strong>storage_format</strong> – format string which will be appled to the tuple <tt class="docutils literal"><span class="pre">(value.year,</span> <span class="pre">value.month,</span> <span class="pre">value.day)</span></tt>, given a Python datetime.date() object.</li> <li><strong>regexp</strong> – regular expression which will be applied to incoming result rows. The resulting match object is appled to the Python date() constructor via <tt class="docutils literal"><span class="pre">*map(int,</span> <span class="pre">match_obj.groups(0))</span></tt>.</li> </ul> </td> </tr> </tbody> </table> </dd></dl> <dl class="class"> <dt id="sqlalchemy.dialects.sqlite.TIME"> <em class="property">class </em><tt class="descclassname">sqlalchemy.dialects.sqlite.</tt><tt class="descname">TIME</tt><big>(</big><em>storage_format=None</em>, <em>regexp=None</em>, <em>**kwargs</em><big>)</big><a class="headerlink" href="#sqlalchemy.dialects.sqlite.TIME" title="Permalink to this definition">¶</a></dt> <dd><p>Represent a Python time object in SQLite using a string.</p> <p>The default string storage format is:</p> <div class="highlight-python"><div class="highlight"><pre><span class="s">"</span><span class="si">%02d</span><span class="s">:</span><span class="si">%02d</span><span class="s">:</span><span class="si">%02d</span><span class="s">.</span><span class="si">%06d</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">value</span><span class="o">.</span><span class="n">hour</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">minute</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">second</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">microsecond</span><span class="p">)</span></pre></div> </div> <p>e.g.:</p> <div class="highlight-python"><pre>12:05:57.10558</pre> </div> <p>The storage format can be customized to some degree using the <tt class="docutils literal"><span class="pre">storage_format</span></tt> and <tt class="docutils literal"><span class="pre">regexp</span></tt> parameters, such as:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">re</span> <span class="kn">from</span> <span class="nn">sqlalchemy.dialects.sqlite</span> <span class="kn">import</span> <span class="n">TIME</span> <span class="n">t</span> <span class="o">=</span> <span class="n">TIME</span><span class="p">(</span> <span class="n">storage_format</span><span class="o">=</span><span class="s">"</span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%02d</span><span class="s">-</span><span class="si">%06d</span><span class="s">"</span><span class="p">,</span> <span class="n">regexp</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s">"(\d+)-(\d+)-(\d+)-(?:-(\d+))?"</span><span class="p">)</span> <span class="p">)</span></pre></div> </div> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple"> <li><strong>storage_format</strong> – format string which will be appled to the tuple <tt class="docutils literal"><span class="pre">(value.hour,</span> <span class="pre">value.minute,</span> <span class="pre">value.second,</span> <span class="pre">value.microsecond)</span></tt>, given a Python datetime.time() object.</li> <li><strong>regexp</strong> – regular expression which will be applied to incoming result rows. The resulting match object is appled to the Python time() constructor via <tt class="docutils literal"><span class="pre">*map(int,</span> <span class="pre">match_obj.groups(0))</span></tt>.</li> </ul> </td> </tr> </tbody> </table> </dd></dl> </div> <div class="section" id="module-sqlalchemy.dialects.sqlite.pysqlite"> <span id="pysqlite"></span><h2>Pysqlite<a class="headerlink" href="#module-sqlalchemy.dialects.sqlite.pysqlite" title="Permalink to this headline">¶</a></h2> <p>Support for the SQLite database via pysqlite.</p> <p>Note that pysqlite is the same driver as the <tt class="docutils literal"><span class="pre">sqlite3</span></tt> module included with the Python distribution.</p> <div class="section" id="driver"> <h3>Driver<a class="headerlink" href="#driver" title="Permalink to this headline">¶</a></h3> <p>When using Python 2.5 and above, the built in <tt class="docutils literal"><span class="pre">sqlite3</span></tt> driver is already installed and no additional installation is needed. Otherwise, the <tt class="docutils literal"><span class="pre">pysqlite2</span></tt> driver needs to be present. This is the same driver as <tt class="docutils literal"><span class="pre">sqlite3</span></tt>, just with a different name.</p> <p>The <tt class="docutils literal"><span class="pre">pysqlite2</span></tt> driver will be loaded first, and if not found, <tt class="docutils literal"><span class="pre">sqlite3</span></tt> is loaded. This allows an explicitly installed pysqlite driver to take precedence over the built in one. As with all dialects, a specific DBAPI module may be provided to <a class="reference internal" href="../core/engines.html#sqlalchemy.create_engine" title="sqlalchemy.create_engine"><tt class="xref py py-func docutils literal"><span class="pre">create_engine()</span></tt></a> to control this explicitly:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlite3</span> <span class="kn">import</span> <span class="n">dbapi2</span> <span class="k">as</span> <span class="n">sqlite</span> <span class="n">e</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite+pysqlite:///file.db'</span><span class="p">,</span> <span class="n">module</span><span class="o">=</span><span class="n">sqlite</span><span class="p">)</span></pre></div> </div> <p>Full documentation on pysqlite is available at: <a class="reference external" href="http://www.initd.org/pub/software/pysqlite/doc/usage-guide.html">http://www.initd.org/pub/software/pysqlite/doc/usage-guide.html</a></p> </div> <div class="section" id="connect-strings"> <h3>Connect Strings<a class="headerlink" href="#connect-strings" title="Permalink to this headline">¶</a></h3> <p>The file specification for the SQLite database is taken as the “database” portion of the URL. Note that the format of a url is:</p> <div class="highlight-python"><pre>driver://user:pass@host/database</pre> </div> <p>This means that the actual filename to be used starts with the characters to the <strong>right</strong> of the third slash. So connecting to a relative filepath looks like:</p> <div class="highlight-python"><div class="highlight"><pre><span class="c"># relative path</span> <span class="n">e</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite:///path/to/database.db'</span><span class="p">)</span></pre></div> </div> <p>An absolute path, which is denoted by starting with a slash, means you need <strong>four</strong> slashes:</p> <div class="highlight-python"><div class="highlight"><pre><span class="c"># absolute path</span> <span class="n">e</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite:////path/to/database.db'</span><span class="p">)</span></pre></div> </div> <p>To use a Windows path, regular drive specifications and backslashes can be used. Double backslashes are probably needed:</p> <div class="highlight-python"><div class="highlight"><pre><span class="c"># absolute path on Windows</span> <span class="n">e</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite:///C:</span><span class="se">\\</span><span class="s">path</span><span class="se">\\</span><span class="s">to</span><span class="se">\\</span><span class="s">database.db'</span><span class="p">)</span></pre></div> </div> <p>The sqlite <tt class="docutils literal"><span class="pre">:memory:</span></tt> identifier is the default if no filepath is present. Specify <tt class="docutils literal"><span class="pre">sqlite://</span></tt> and nothing else:</p> <div class="highlight-python"><div class="highlight"><pre><span class="c"># in-memory database</span> <span class="n">e</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite://'</span><span class="p">)</span></pre></div> </div> </div> <div class="section" id="compatibility-with-sqlite3-native-date-and-datetime-types"> <h3>Compatibility with sqlite3 “native” date and datetime types<a class="headerlink" href="#compatibility-with-sqlite3-native-date-and-datetime-types" title="Permalink to this headline">¶</a></h3> <p>The pysqlite driver includes the sqlite3.PARSE_DECLTYPES and sqlite3.PARSE_COLNAMES options, which have the effect of any column or expression explicitly cast as “date” or “timestamp” will be converted to a Python date or datetime object. The date and datetime types provided with the pysqlite dialect are not currently compatible with these options, since they render the ISO date/datetime including microseconds, which pysqlite’s driver does not. Additionally, SQLAlchemy does not at this time automatically render the “cast” syntax required for the freestanding functions “current_timestamp” and “current_date” to return datetime/date types natively. Unfortunately, pysqlite does not provide the standard DBAPI types in <tt class="docutils literal"><span class="pre">cursor.description</span></tt>, leaving SQLAlchemy with no way to detect these types on the fly without expensive per-row type checks.</p> <p>Keeping in mind that pysqlite’s parsing option is not recommended, nor should be necessary, for use with SQLAlchemy, usage of PARSE_DECLTYPES can be forced if one configures “native_datetime=True” on create_engine():</p> <div class="highlight-python"><div class="highlight"><pre><span class="n">engine</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite://'</span><span class="p">,</span> <span class="n">connect_args</span><span class="o">=</span><span class="p">{</span><span class="s">'detect_types'</span><span class="p">:</span> <span class="n">sqlite3</span><span class="o">.</span><span class="n">PARSE_DECLTYPES</span><span class="o">|</span><span class="n">sqlite3</span><span class="o">.</span><span class="n">PARSE_COLNAMES</span><span class="p">},</span> <span class="n">native_datetime</span><span class="o">=</span><span class="bp">True</span> <span class="p">)</span></pre></div> </div> <p>With this flag enabled, the DATE and TIMESTAMP types (but note - not the DATETIME or TIME types...confused yet ?) will not perform any bind parameter or result processing. Execution of “func.current_date()” will return a string. “func.current_timestamp()” is registered as returning a DATETIME type in SQLAlchemy, so this function still receives SQLAlchemy-level result processing.</p> </div> <div class="section" id="threading-behavior"> <h3>Threading Behavior<a class="headerlink" href="#threading-behavior" title="Permalink to this headline">¶</a></h3> <p>Pysqlite connections do not support being moved between threads, unless the <tt class="docutils literal"><span class="pre">check_same_thread</span></tt> Pysqlite flag is set to <tt class="xref docutils literal"><span class="pre">False</span></tt>. In addition, when using an in-memory SQLite database, the full database exists only within the scope of a single connection. It is reported that an in-memory database does not support being shared between threads regardless of the <tt class="docutils literal"><span class="pre">check_same_thread</span></tt> flag - which means that a multithreaded application <strong>cannot</strong> share data from a <tt class="docutils literal"><span class="pre">:memory:</span></tt> database across threads unless access to the connection is limited to a single worker thread which communicates through a queueing mechanism to concurrent threads.</p> <p>To provide a default which accomodates SQLite’s default threading capabilities somewhat reasonably, the SQLite dialect will specify that the <a class="reference internal" href="../core/pooling.html#sqlalchemy.pool.SingletonThreadPool" title="sqlalchemy.pool.SingletonThreadPool"><tt class="xref py py-class docutils literal"><span class="pre">SingletonThreadPool</span></tt></a> be used by default. This pool maintains a single SQLite connection per thread that is held open up to a count of five concurrent threads. When more than five threads are used, a cleanup mechanism will dispose of excess unused connections.</p> <p>Two optional pool implementations that may be appropriate for particular SQLite usage scenarios:</p> <blockquote> <div><ul class="simple"> <li>the <a class="reference internal" href="../core/pooling.html#sqlalchemy.pool.StaticPool" title="sqlalchemy.pool.StaticPool"><tt class="xref py py-class docutils literal"><span class="pre">sqlalchemy.pool.StaticPool</span></tt></a> might be appropriate for a multithreaded application using an in-memory database, assuming the threading issues inherent in pysqlite are somehow accomodated for. This pool holds persistently onto a single connection which is never closed, and is returned for all requests.</li> <li>the <a class="reference internal" href="../core/pooling.html#sqlalchemy.pool.NullPool" title="sqlalchemy.pool.NullPool"><tt class="xref py py-class docutils literal"><span class="pre">sqlalchemy.pool.NullPool</span></tt></a> might be appropriate for an application that makes use of a file-based sqlite database. This pool disables any actual “pooling” behavior, and simply opens and closes real connections corresonding to the <tt class="xref py py-func docutils literal"><span class="pre">connect()</span></tt> and <tt class="xref py py-func docutils literal"><span class="pre">close()</span></tt> methods. SQLite can “connect” to a particular file with very high efficiency, so this option may actually perform better without the extra overhead of <tt class="xref py py-class docutils literal"><span class="pre">SingletonThreadPool</span></tt>. NullPool will of course render a <tt class="docutils literal"><span class="pre">:memory:</span></tt> connection useless since the database would be lost as soon as the connection is “returned” to the pool.</li> </ul> </div></blockquote> </div> <div class="section" id="unicode"> <h3>Unicode<a class="headerlink" href="#unicode" title="Permalink to this headline">¶</a></h3> <p>In contrast to SQLAlchemy’s active handling of date and time types for pysqlite, pysqlite’s default behavior regarding Unicode is that all strings are returned as Python unicode objects in all cases. So even if the <a class="reference internal" href="../core/types.html#sqlalchemy.types.Unicode" title="sqlalchemy.types.Unicode"><tt class="xref py py-class docutils literal"><span class="pre">Unicode</span></tt></a> type is <em>not</em> used, you will still always receive unicode data back from a result set. It is <strong>strongly</strong> recommended that you do use the <a class="reference internal" href="../core/types.html#sqlalchemy.types.Unicode" title="sqlalchemy.types.Unicode"><tt class="xref py py-class docutils literal"><span class="pre">Unicode</span></tt></a> type to represent strings, since it will raise a warning if a non-unicode Python string is passed from the user application. Mixing the usage of non-unicode objects with returned unicode objects can quickly create confusion, particularly when using the ORM as internal data is not always represented by an actual database result string.</p> </div> </div> </div> </div> </div> <div class="bottomnav"> Previous: <a href="postgresql.html" title="previous chapter">PostgreSQL</a> Next: <a href="sybase.html" title="next chapter">Sybase</a> <div class="doc_copyright"> © <a href="../copyright.html">Copyright</a> 2007-2011, the SQLAlchemy authors and contributors. 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