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  • Committer: Package Import Robot
  • Author(s): Piotr Ożarowski
  • Date: 2013-10-28 22:29:40 UTC
  • mfrom: (1.4.24)
  • Revision ID: package-import@ubuntu.com-20131028222940-wvyqffl4g617caun
Tags: 0.8.3-1
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doc/orm/extensions/hybrid.html
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    <script type="text/javascript">
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      var DOCUMENTATION_OPTIONS = {
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          URL_ROOT:    '../../',
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          VERSION:     '0.8.2',
 
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          VERSION:     '0.8.3',
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          COLLAPSE_MODINDEX: false,
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          FILE_SUFFIX: '.html'
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      };
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    </div>
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    <div id="docs-version-header">
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        Release: <span class="version-num">0.8.2</span> | Release Date: July 3, 2013
 
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        Release: <span class="version-num">0.8.3</span> | Release Date: October 26, 2013
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    </div>
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            <span class="n">account</span> <span class="o">=</span> <span class="n">Account</span><span class="p">(</span><span class="n">owner</span><span class="o">=</span><span class="bp">self</span><span class="p">)</span>
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        <span class="k">else</span><span class="p">:</span>
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            <span class="n">account</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">accounts</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
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        <span class="n">account</span><span class="o">.</span><span class="n">balance</span> <span class="o">=</span> <span class="n">balance</span>
 
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        <span class="n">account</span><span class="o">.</span><span class="n">balance</span> <span class="o">=</span> <span class="n">value</span>
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    <span class="nd">@balance.expression</span>
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    <span class="k">def</span> <span class="nf">balance</span><span class="p">(</span><span class="n">cls</span><span class="p">):</span>
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<h3>Correlated Subquery Relationship Hybrid<a class="headerlink" href="#correlated-subquery-relationship-hybrid" title="Permalink to this headline">¶</a></h3>
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<p>We can, of course, forego being dependent on the enclosing query&#8217;s usage
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of joins in favor of the correlated subquery, which can portably be packed
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into a single colunn expression. A correlated subquery is more portable, but
 
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into a single column expression. A correlated subquery is more portable, but
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often performs more poorly at the SQL level. Using the same technique
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illustrated at <a class="reference internal" href="../mapper_config.html#mapper-column-property-sql-expressions"><em>Using column_property</em></a>,
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we can adjust our <tt class="docutils literal"><span class="pre">SavingsAccount</span></tt> example to aggregate the balances for
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<span class="go">WHERE lower(searchword.word) = lower(:lower_1)</span></pre></div>
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</div>
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<p>The <tt class="docutils literal"><span class="pre">CaseInsensitiveComparator</span></tt> above implements part of the
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<a class="reference internal" href="../../core/expression_api.html#sqlalchemy.sql.operators.ColumnOperators" title="sqlalchemy.sql.operators.ColumnOperators"><tt class="xref py py-class docutils literal"><span class="pre">ColumnOperators</span></tt></a> interface.   A &#8220;coercion&#8221; operation like
 
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<a class="reference internal" href="../../core/sqlelement.html#sqlalchemy.sql.operators.ColumnOperators" title="sqlalchemy.sql.operators.ColumnOperators"><tt class="xref py py-class docutils literal"><span class="pre">ColumnOperators</span></tt></a> interface.   A &#8220;coercion&#8221; operation like
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lowercasing can be applied to all comparison operations (i.e. <tt class="docutils literal"><span class="pre">eq</span></tt>,
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<tt class="docutils literal"><span class="pre">lt</span></tt>, <tt class="docutils literal"><span class="pre">gt</span></tt>, etc.) using <a class="reference internal" href="../../core/expression_api.html#sqlalchemy.sql.operators.Operators.operate" title="sqlalchemy.sql.operators.Operators.operate"><tt class="xref py py-meth docutils literal"><span class="pre">Operators.operate()</span></tt></a>:</p>
 
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<tt class="docutils literal"><span class="pre">lt</span></tt>, <tt class="docutils literal"><span class="pre">gt</span></tt>, etc.) using <a class="reference internal" href="../../core/sqlelement.html#sqlalchemy.sql.operators.Operators.operate" title="sqlalchemy.sql.operators.Operators.operate"><tt class="xref py py-meth docutils literal"><span class="pre">Operators.operate()</span></tt></a>:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">CaseInsensitiveComparator</span><span class="p">(</span><span class="n">Comparator</span><span class="p">):</span>
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    <span class="k">def</span> <span class="nf">operate</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">op</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
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        <span class="k">return</span> <span class="n">op</span><span class="p">(</span><span class="n">func</span><span class="o">.</span><span class="n">lower</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">__clause_element__</span><span class="p">()),</span> <span class="n">func</span><span class="o">.</span><span class="n">lower</span><span class="p">(</span><span class="n">other</span><span class="p">))</span></pre></div>
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<p>The Hybrid Value pattern is very useful for any kind of value that may
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have multiple representations, such as timestamps, time deltas, units
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of measurement, currencies and encrypted passwords.</p>
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<div class="admonition-see-also admonition seealso">
 
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<div class="admonition seealso">
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<p class="first admonition-title">See also</p>
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<p><a class="reference external" href="http://techspot.zzzeek.org/2011/10/21/hybrids-and-value-agnostic-types/">Hybrids and Value Agnostic Types</a> -
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on the techspot.zzzeek.org blog</p>
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        <span class="k">return</span> <span class="n">GrandparentTransformer</span><span class="p">(</span><span class="n">cls</span><span class="p">)</span></pre></div>
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</div>
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<p>The <tt class="docutils literal"><span class="pre">GrandparentTransformer</span></tt> overrides the core
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<a class="reference internal" href="../../core/expression_api.html#sqlalchemy.sql.operators.Operators.operate" title="sqlalchemy.sql.operators.Operators.operate"><tt class="xref py py-meth docutils literal"><span class="pre">Operators.operate()</span></tt></a> method at the base of the
 
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<a class="reference internal" href="../../core/sqlelement.html#sqlalchemy.sql.operators.Operators.operate" title="sqlalchemy.sql.operators.Operators.operate"><tt class="xref py py-meth docutils literal"><span class="pre">Operators.operate()</span></tt></a> method at the base of the
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<a class="reference internal" href="#sqlalchemy.ext.hybrid.Comparator" title="sqlalchemy.ext.hybrid.Comparator"><tt class="xref py py-class docutils literal"><span class="pre">Comparator</span></tt></a> hierarchy to return a query-transforming
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callable, which then runs the given comparison operation in a
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particular context. Such as, in the example above, the <tt class="docutils literal"><span class="pre">operate</span></tt>
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<dl class="class">
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<dt id="sqlalchemy.ext.hybrid.hybrid_method">
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<em class="property">class </em><tt class="descclassname">sqlalchemy.ext.hybrid.</tt><tt class="descname">hybrid_method</tt><big>(</big><em>func</em>, <em>expr=None</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.hybrid.hybrid_method" title="Permalink to this definition">¶</a></dt>
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<dd><p>A decorator which allows definition of a Python object method with both
 
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<dd><p>Bases: <a class="reference internal" href="../internals.html#sqlalchemy.orm.interfaces._InspectionAttr" title="sqlalchemy.orm.interfaces._InspectionAttr"><tt class="xref py py-class docutils literal"><span class="pre">sqlalchemy.orm.interfaces._InspectionAttr</span></tt></a></p>
 
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<p>A decorator which allows definition of a Python object method with both
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instance-level and class-level behavior.</p>
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<dl class="method">
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<dt id="sqlalchemy.ext.hybrid.hybrid_method.__init__">
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<dl class="class">
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<dt id="sqlalchemy.ext.hybrid.hybrid_property">
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<em class="property">class </em><tt class="descclassname">sqlalchemy.ext.hybrid.</tt><tt class="descname">hybrid_property</tt><big>(</big><em>fget</em>, <em>fset=None</em>, <em>fdel=None</em>, <em>expr=None</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.hybrid.hybrid_property" title="Permalink to this definition">¶</a></dt>
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<dd><p>A decorator which allows definition of a Python descriptor with both
 
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<dd><p>Bases: <a class="reference internal" href="../internals.html#sqlalchemy.orm.interfaces._InspectionAttr" title="sqlalchemy.orm.interfaces._InspectionAttr"><tt class="xref py py-class docutils literal"><span class="pre">sqlalchemy.orm.interfaces._InspectionAttr</span></tt></a></p>
 
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<p>A decorator which allows definition of a Python descriptor with both
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instance-level and class-level behavior.</p>
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<dl class="method">
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<dt id="sqlalchemy.ext.hybrid.hybrid_property.__init__">
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    <div id="docs-copyright">
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        &copy; <a href="../../copyright.html">Copyright</a> 2007-2013, the SQLAlchemy authors and contributors.
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        Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
 
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        Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.2b1.
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    </div>
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</div>
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