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Firebird
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<h1>SQLAlchemy 0.6.8 Documentation</h1>
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Version: <span class="versionnum">0.6.8</span> Last Updated: 06/05/2011 13:10:26
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Firebird
<h2>
Firebird
</h2>
<ul>
<li><a class="reference internal" href="#">Firebird</a><ul>
<li><a class="reference internal" href="#dialects">Dialects</a></li>
<li><a class="reference internal" href="#locking-behavior">Locking Behavior</a></li>
<li><a class="reference internal" href="#returning-support">RETURNING support</a></li>
<li><a class="reference internal" href="#kinterbasdb">kinterbasdb</a></li>
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<div class="section" id="module-sqlalchemy.dialects.firebird.base">
<span id="firebird"></span><h1>Firebird<a class="headerlink" href="#module-sqlalchemy.dialects.firebird.base" title="Permalink to this headline">¶</a></h1>
<p>Support for the Firebird database.</p>
<p>Connectivity is usually supplied via the <a class="reference internal" href="#kinterbasdb">kinterbasdb</a> DBAPI module.</p>
<div class="section" id="dialects">
<h2>Dialects<a class="headerlink" href="#dialects" title="Permalink to this headline">¶</a></h2>
<p>Firebird offers two distinct <a class="reference external" href="http://mc-computing.com/Databases/Firebird/SQL_Dialect.html">dialects</a> (not to be confused with a
SQLAlchemy <tt class="docutils literal"><span class="pre">Dialect</span></tt>):</p>
<dl class="docutils">
<dt>dialect 1</dt>
<dd>This is the old syntax and behaviour, inherited from Interbase pre-6.0.</dd>
<dt>dialect 3</dt>
<dd>This is the newer and supported syntax, introduced in Interbase 6.0.</dd>
</dl>
<p>The SQLAlchemy Firebird dialect detects these versions and
adjusts its representation of SQL accordingly. However,
support for dialect 1 is not well tested and probably has
incompatibilities.</p>
</div>
<div class="section" id="locking-behavior">
<h2>Locking Behavior<a class="headerlink" href="#locking-behavior" title="Permalink to this headline">¶</a></h2>
<p>Firebird locks tables aggressively. For this reason, a DROP TABLE may
hang until other transactions are released. SQLAlchemy does its best
to release transactions as quickly as possible. The most common cause
of hanging transactions is a non-fully consumed result set, i.e.:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">result</span> <span class="o">=</span> <span class="n">engine</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s">"select * from table"</span><span class="p">)</span>
<span class="n">row</span> <span class="o">=</span> <span class="n">result</span><span class="o">.</span><span class="n">fetchone</span><span class="p">()</span>
<span class="k">return</span></pre></div>
</div>
<p>Where above, the <tt class="docutils literal"><span class="pre">ResultProxy</span></tt> has not been fully consumed. The
connection will be returned to the pool and the transactional state
rolled back once the Python garbage collector reclaims the objects
which hold onto the connection, which often occurs asynchronously.
The above use case can be alleviated by calling <tt class="docutils literal"><span class="pre">first()</span></tt> on the
<tt class="docutils literal"><span class="pre">ResultProxy</span></tt> which will fetch the first row and immediately close
all remaining cursor/connection resources.</p>
</div>
<div class="section" id="returning-support">
<h2>RETURNING support<a class="headerlink" href="#returning-support" title="Permalink to this headline">¶</a></h2>
<p>Firebird 2.0 supports returning a result set from inserts, and 2.1
extends that to deletes and updates. This is generically exposed by
the SQLAlchemy <tt class="docutils literal"><span class="pre">returning()</span></tt> method, such as:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># INSERT..RETURNING</span>
<span class="n">result</span> <span class="o">=</span> <span class="n">table</span><span class="o">.</span><span class="n">insert</span><span class="p">()</span><span class="o">.</span><span class="n">returning</span><span class="p">(</span><span class="n">table</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">col1</span><span class="p">,</span> <span class="n">table</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">col2</span><span class="p">)</span><span class="o">.</span>\
<span class="n">values</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">'foo'</span><span class="p">)</span>
<span class="k">print</span> <span class="n">result</span><span class="o">.</span><span class="n">fetchall</span><span class="p">()</span>
<span class="c"># UPDATE..RETURNING</span>
<span class="n">raises</span> <span class="o">=</span> <span class="n">empl</span><span class="o">.</span><span class="n">update</span><span class="p">()</span><span class="o">.</span><span class="n">returning</span><span class="p">(</span><span class="n">empl</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">id</span><span class="p">,</span> <span class="n">empl</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">salary</span><span class="p">)</span><span class="o">.</span>\
<span class="n">where</span><span class="p">(</span><span class="n">empl</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">sales</span><span class="o">></span><span class="mi">100</span><span class="p">)</span><span class="o">.</span>\
<span class="n">values</span><span class="p">(</span><span class="nb">dict</span><span class="p">(</span><span class="n">salary</span><span class="o">=</span><span class="n">empl</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">salary</span> <span class="o">*</span> <span class="mf">1.1</span><span class="p">))</span>
<span class="k">print</span> <span class="n">raises</span><span class="o">.</span><span class="n">fetchall</span><span class="p">()</span></pre></div>
</div>
</div>
<div class="section" id="kinterbasdb">
<span id="id2"></span><h2>kinterbasdb<a class="headerlink" href="#kinterbasdb" title="Permalink to this headline">¶</a></h2>
<span class="target" id="module-sqlalchemy.dialects.firebird.kinterbasdb"></span><p>The most common way to connect to a Firebird engine is implemented by
<a class="reference external" href="http://sourceforge.net/projects/kinterbasdb">kinterbasdb</a>, currently <a class="reference external" href="http://firebirdsql.org/index.php?op=devel&sub=python">maintained</a> directly by the Firebird people.</p>
<p>The connection URL is of the form
<tt class="docutils literal"><span class="pre">firebird[+kinterbasdb]://user:password@host:port/path/to/db[?key=value&key=value...]</span></tt>.</p>
<p>Kinterbasedb backend specific keyword arguments are:</p>
<ul>
<li><p class="first">type_conv - select the kind of mapping done on the types: by default
SQLAlchemy uses 200 with Unicode, datetime and decimal support (see
<a class="reference external" href="http://kinterbasdb.sourceforge.net/dist_docs/usage.html#adv_param_conv_dynamic_type_translation">details</a>).</p>
</li>
<li><p class="first">concurrency_level - set the backend policy with regards to threading
issues: by default SQLAlchemy uses policy 1 (see <a class="reference external" href="http://kinterbasdb.sourceforge.net/dist_docs/usage.html#special_issue_concurrency">details</a>).</p>
</li>
<li><p class="first">enable_rowcount - True by default, setting this to False disables
the usage of “cursor.rowcount” with the
Kinterbasdb dialect, which SQLAlchemy ordinarily calls upon automatically
after any UPDATE or DELETE statement. When disabled, SQLAlchemy’s
ResultProxy will return -1 for result.rowcount. The rationale here is
that Kinterbasdb requires a second round trip to the database when
.rowcount is called - since SQLA’s resultproxy automatically closes
the cursor after a non-result-returning statement, rowcount must be
called, if at all, before the result object is returned. Additionally,
cursor.rowcount may not return correct results with older versions
of Firebird, and setting this flag to False will also cause the
SQLAlchemy ORM to ignore its usage. The behavior can also be controlled on a
per-execution basis using the <cite>enable_rowcount</cite> option with
<tt class="xref py py-meth docutils literal"><span class="pre">execution_options()</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">conn</span> <span class="o">=</span> <span class="n">engine</span><span class="o">.</span><span class="n">connect</span><span class="p">()</span><span class="o">.</span><span class="n">execution_options</span><span class="p">(</span><span class="n">enable_rowcount</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">r</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="n">stmt</span><span class="p">)</span>
<span class="k">print</span> <span class="n">r</span><span class="o">.</span><span class="n">rowcount</span></pre></div>
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