File: //usr/share/doc/python-sqlalchemy-0.9.8/doc/_modules/examples/join_conditions/cast.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>
examples.join_conditions.cast
—
SQLAlchemy 0.9 Documentation
</title>
<!-- begin iterate through SQLA + sphinx environment css_files -->
<link rel="stylesheet" href="../../../_static/pygments.css" type="text/css" />
<link rel="stylesheet" href="../../../_static/docs.css" type="text/css" />
<link rel="stylesheet" href="../../../_static/sphinx_paramlinks.css" type="text/css" />
<link rel="stylesheet" href="../../../_static/changelog.css" type="text/css" />
<!-- end iterate through SQLA + sphinx environment css_files -->
<!-- begin layout.mako headers -->
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '../../../',
VERSION: '0.9.8',
COLLAPSE_MODINDEX: false,
FILE_SUFFIX: '.html'
};
</script>
<!-- begin iterate through sphinx environment script_files -->
<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>
<!-- end iterate through sphinx environment script_files -->
<script type="text/javascript" src="../../../_static/detectmobile.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 0.9 Documentation" href="../../../index.html" />
<link rel="up" title="Module code" href="../../index.html" />
<!-- end layout.mako headers -->
</head>
<body>
<div id="docs-container">
<div id="docs-top-navigation-container" class="body-background">
<div id="docs-header">
<div id="docs-version-header">
Release: <span class="version-num">0.9.8</span> | Release Date: October 13, 2014
</div>
<h1>SQLAlchemy 0.9 Documentation</h1>
</div>
</div>
<div id="docs-body-container">
<div id="fixed-sidebar" class="">
<div id="index-nav">
<form class="search" action="../../../search.html" method="get">
<input type="text" name="q" size="12" /> <input type="submit" value="Search" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
<p>
<a href="../../../index.html">Contents</a> |
<a href="../../../genindex.html">Index</a>
</p>
</div>
</div>
<div id="docs-body" class="" >
<h1>Source code for examples.join_conditions.cast</h1><div class="highlight"><pre>
<span class="sd">"""Illustrate a :func:`.relationship` that joins two columns where those</span>
<span class="sd">columns are not of the same type, and a CAST must be used on the SQL</span>
<span class="sd">side in order to match them.</span>
<span class="sd">When complete, we'd like to see a load of the relationship to look like::</span>
<span class="sd"> -- load the primary row, a_id is a string</span>
<span class="sd"> SELECT a.id AS a_id_1, a.a_id AS a_a_id</span>
<span class="sd"> FROM a</span>
<span class="sd"> WHERE a.a_id = '2'</span>
<span class="sd"> -- then load the collection using CAST, b.a_id is an integer</span>
<span class="sd"> SELECT b.id AS b_id, b.a_id AS b_a_id</span>
<span class="sd"> FROM b</span>
<span class="sd"> WHERE CAST('2' AS INTEGER) = b.a_id</span>
<span class="sd">The relationship is essentially configured as follows::</span>
<span class="sd"> class B(Base):</span>
<span class="sd"> # ...</span>
<span class="sd"> a = relationship(A,</span>
<span class="sd"> primaryjoin=cast(A.a_id, Integer) == foreign(B.a_id),</span>
<span class="sd"> backref="bs")</span>
<span class="sd">Where above, we are making use of the :func:`.cast` function in order</span>
<span class="sd">to produce CAST, as well as the :func:`.foreign` :term:`annotation` function</span>
<span class="sd">in order to note to the ORM that ``B.a_id`` should be treated like the</span>
<span class="sd">"foreign key" column.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.ext.declarative</span> <span class="kn">import</span> <span class="n">declarative_base</span>
<span class="n">Base</span> <span class="o">=</span> <span class="n">declarative_base</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">StringAsInt</span><span class="p">(</span><span class="n">TypeDecorator</span><span class="p">):</span>
<span class="sd">"""Coerce string->integer type.</span>
<span class="sd"> This is needed only if the relationship() from</span>
<span class="sd"> int to string is writable, as SQLAlchemy will copy</span>
<span class="sd"> the string parent values into the integer attribute</span>
<span class="sd"> on the child during a flush.</span>
<span class="sd"> """</span>
<span class="n">impl</span> <span class="o">=</span> <span class="n">Integer</span>
<span class="k">def</span> <span class="nf">process_bind_param</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">dialect</span><span class="p">):</span>
<span class="k">if</span> <span class="n">value</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span><span class="p">:</span>
<span class="n">value</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">return</span> <span class="n">value</span>
<span class="k">class</span> <span class="nc">A</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="sd">"""Parent. The referenced column is a string type."""</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s">'a'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</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">a_id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">B</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="sd">"""Child. The column we reference 'A' with is an integer."""</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s">'b'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</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">a_id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">StringAsInt</span><span class="p">)</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s">"A"</span><span class="p">,</span>
<span class="c"># specify primaryjoin. The string form is optional</span>
<span class="c"># here, but note that Declarative makes available all</span>
<span class="c"># of the built-in functions we might need, including</span>
<span class="c"># cast() and foreign().</span>
<span class="n">primaryjoin</span><span class="o">=</span><span class="s">"cast(A.a_id, Integer) == foreign(B.a_id)"</span><span class="p">,</span>
<span class="n">backref</span><span class="o">=</span><span class="s">"bs"</span><span class="p">)</span>
<span class="c"># we demonstrate with SQLite, but the important part</span>
<span class="c"># is the CAST rendered in the SQL output.</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> <span class="n">echo</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">Base</span><span class="o">.</span><span class="n">metadata</span><span class="o">.</span><span class="n">create_all</span><span class="p">(</span><span class="n">e</span><span class="p">)</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">Session</span><span class="p">(</span><span class="n">e</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">add_all</span><span class="p">([</span>
<span class="n">A</span><span class="p">(</span><span class="n">a_id</span><span class="o">=</span><span class="s">"1"</span><span class="p">),</span>
<span class="n">A</span><span class="p">(</span><span class="n">a_id</span><span class="o">=</span><span class="s">"2"</span><span class="p">,</span> <span class="n">bs</span><span class="o">=</span><span class="p">[</span><span class="n">B</span><span class="p">(),</span> <span class="n">B</span><span class="p">()]),</span>
<span class="n">A</span><span class="p">(</span><span class="n">a_id</span><span class="o">=</span><span class="s">"3"</span><span class="p">,</span> <span class="n">bs</span><span class="o">=</span><span class="p">[</span><span class="n">B</span><span class="p">()]),</span>
<span class="p">])</span>
<span class="n">s</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span>
<span class="n">b1</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">B</span><span class="p">)</span><span class="o">.</span><span class="n">filter_by</span><span class="p">(</span><span class="n">a_id</span><span class="o">=</span><span class="s">"2"</span><span class="p">)</span><span class="o">.</span><span class="n">first</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="n">b1</span><span class="o">.</span><span class="n">a</span><span class="p">)</span>
<span class="n">a1</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">A</span><span class="p">)</span><span class="o">.</span><span class="n">filter_by</span><span class="p">(</span><span class="n">a_id</span><span class="o">=</span><span class="s">"2"</span><span class="p">)</span><span class="o">.</span><span class="n">first</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="p">)</span></pre></div>
</div>
</div>
<div id="docs-bottom-navigation" class="docs-navigation-links">
<div id="docs-copyright">
© <a href="../../../copyright.html">Copyright</a> 2007-2014, the SQLAlchemy authors and contributors.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.2b1.
</div>
</div>
</div>
</body>
</html>