<!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 1.2 Documentation </title> <!-- begin iterate through site-imported + 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/changelog.css" type="text/css" /> <link rel="stylesheet" href="../../../_static/sphinx_paramlinks.css" type="text/css" /> <!-- end iterate through site-imported + sphinx environment css_files --> <!-- begin layout.mako headers --> <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 1.2 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">1.2.19</span> | Release Date: April 15, 2019 </div> <h1>SQLAlchemy 1.2 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"> <label> Search terms: <input type="text" placeholder="search..." name="q" size="12" /> </label> <input type="submit" value="Search" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p> <a href="../../../contents.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></span><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="k">import</span> <span class="n">Column</span> <span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">create_engine</span> <span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">Integer</span> <span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">String</span> <span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">TypeDecorator</span> <span class="kn">from</span> <span class="nn">sqlalchemy.ext.declarative</span> <span class="k">import</span> <span class="n">declarative_base</span> <span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">relationship</span> <span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">Session</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="kc">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="s2">"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="kc">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="s2">"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="kc">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="s2">"A"</span><span class="p">,</span> <span class="c1"># specify primaryjoin. The string form is optional</span> <span class="c1"># here, but note that Declarative makes available all</span> <span class="c1"># of the built-in functions we might need, including</span> <span class="c1"># cast() and foreign().</span> <span class="n">primaryjoin</span><span class="o">=</span><span class="s2">"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="s2">"bs"</span><span class="p">,</span> <span class="p">)</span> <span class="c1"># we demonstrate with SQLite, but the important part</span> <span class="c1"># 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="s2">"sqlite://"</span><span class="p">,</span> <span class="n">echo</span><span class="o">=</span><span class="kc">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="s2">"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="s2">"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="s2">"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="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="s2">"2"</span><span class="p">)</span><span class="o">.</span><span class="n">first</span><span class="p">()</span> <span class="nb">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="s2">"2"</span><span class="p">)</span><span class="o">.</span><span class="n">first</span><span class="p">()</span> <span class="nb">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> 2007-2019, the SQLAlchemy authors and contributors. 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