<!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.generic_associations.generic_fk — 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.generic_associations.generic_fk</h1><div class="highlight"><pre> <span></span><span class="sd">"""Illustrates a so-called "generic foreign key", in a similar fashion</span> <span class="sd">to that of popular frameworks such as Django, ROR, etc. This</span> <span class="sd">approach bypasses standard referential integrity</span> <span class="sd">practices, in that the "foreign key" column is not actually</span> <span class="sd">constrained to refer to any particular table; instead,</span> <span class="sd">in-application logic is used to determine which table is referenced.</span> <span class="sd">This approach is not in line with SQLAlchemy's usual style, as foregoing</span> <span class="sd">foreign key integrity means that the tables can easily contain invalid</span> <span class="sd">references and also have no ability to use in-database cascade functionality.</span> <span class="sd">However, due to the popularity of these systems, as well as that it uses</span> <span class="sd">the fewest number of tables (which doesn't really offer any "advantage",</span> <span class="sd">though seems to be comforting to many) this recipe remains in</span> <span class="sd">high demand, so in the interests of having an easy StackOverflow answer</span> <span class="sd">queued up, here it is. The author recommends "table_per_related"</span> <span class="sd">or "table_per_association" instead of this approach.</span> <span class="sd">.. versionadded:: 0.8.3</span> <span class="sd">"""</span> <span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">and_</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">event</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.ext.declarative</span> <span class="k">import</span> <span class="n">as_declarative</span> <span class="kn">from</span> <span class="nn">sqlalchemy.ext.declarative</span> <span class="k">import</span> <span class="n">declared_attr</span> <span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">backref</span> <span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">foreign</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">remote</span> <span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">Session</span> <span class="nd">@as_declarative</span><span class="p">()</span> <span class="k">class</span> <span class="nc">Base</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="sd">"""Base class which provides automated table name</span> <span class="sd"> and surrogate primary key column.</span> <span class="sd"> """</span> <span class="nd">@declared_attr</span> <span class="k">def</span> <span class="nf">__tablename__</span><span class="p">(</span><span class="bp">cls</span><span class="p">):</span> <span class="k">return</span> <span class="bp">cls</span><span class="o">.</span><span class="vm">__name__</span><span class="o">.</span><span class="n">lower</span><span class="p">()</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="k">class</span> <span class="nc">Address</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span> <span class="sd">"""The Address class.</span> <span class="sd"> This represents all address records in a</span> <span class="sd"> single table.</span> <span class="sd"> """</span> <span class="n">street</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="n">city</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="nb">zip</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="n">discriminator</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="sd">"""Refers to the type of parent."""</span> <span class="n">parent_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="sd">"""Refers to the primary key of the parent.</span> <span class="sd"> This could refer to any table.</span> <span class="sd"> """</span> <span class="nd">@property</span> <span class="k">def</span> <span class="nf">parent</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="sd">"""Provides in-Python access to the "parent" by choosing</span> <span class="sd"> the appropriate relationship.</span> <span class="sd"> """</span> <span class="k">return</span> <span class="nb">getattr</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="s2">"parent_</span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="bp">self</span><span class="o">.</span><span class="n">discriminator</span><span class="p">)</span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="s2">"</span><span class="si">%s</span><span class="s2">(street=</span><span class="si">%r</span><span class="s2">, city=</span><span class="si">%r</span><span class="s2">, zip=</span><span class="si">%r</span><span class="s2">)"</span> <span class="o">%</span> <span class="p">(</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span><span class="o">.</span><span class="vm">__name__</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">street</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">city</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">zip</span><span class="p">,</span> <span class="p">)</span> <span class="k">class</span> <span class="nc">HasAddresses</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="sd">"""HasAddresses mixin, creates a relationship to</span> <span class="sd"> the address_association table for each parent.</span> <span class="sd"> """</span> <span class="nd">@event</span><span class="o">.</span><span class="n">listens_for</span><span class="p">(</span><span class="n">HasAddresses</span><span class="p">,</span> <span class="s2">"mapper_configured"</span><span class="p">,</span> <span class="n">propagate</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="k">def</span> <span class="nf">setup_listener</span><span class="p">(</span><span class="n">mapper</span><span class="p">,</span> <span class="n">class_</span><span class="p">):</span> <span class="n">name</span> <span class="o">=</span> <span class="n">class_</span><span class="o">.</span><span class="vm">__name__</span> <span class="n">discriminator</span> <span class="o">=</span> <span class="n">name</span><span class="o">.</span><span class="n">lower</span><span class="p">()</span> <span class="n">class_</span><span class="o">.</span><span class="n">addresses</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span> <span class="n">Address</span><span class="p">,</span> <span class="n">primaryjoin</span><span class="o">=</span><span class="n">and_</span><span class="p">(</span> <span class="n">class_</span><span class="o">.</span><span class="n">id</span> <span class="o">==</span> <span class="n">foreign</span><span class="p">(</span><span class="n">remote</span><span class="p">(</span><span class="n">Address</span><span class="o">.</span><span class="n">parent_id</span><span class="p">)),</span> <span class="n">Address</span><span class="o">.</span><span class="n">discriminator</span> <span class="o">==</span> <span class="n">discriminator</span><span class="p">,</span> <span class="p">),</span> <span class="n">backref</span><span class="o">=</span><span class="n">backref</span><span class="p">(</span> <span class="s2">"parent_</span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="n">discriminator</span><span class="p">,</span> <span class="n">primaryjoin</span><span class="o">=</span><span class="n">remote</span><span class="p">(</span><span class="n">class_</span><span class="o">.</span><span class="n">id</span><span class="p">)</span> <span class="o">==</span> <span class="n">foreign</span><span class="p">(</span><span class="n">Address</span><span class="o">.</span><span class="n">parent_id</span><span class="p">),</span> <span class="p">),</span> <span class="p">)</span> <span class="nd">@event</span><span class="o">.</span><span class="n">listens_for</span><span class="p">(</span><span class="n">class_</span><span class="o">.</span><span class="n">addresses</span><span class="p">,</span> <span class="s2">"append"</span><span class="p">)</span> <span class="k">def</span> <span class="nf">append_address</span><span class="p">(</span><span class="n">target</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">initiator</span><span class="p">):</span> <span class="n">value</span><span class="o">.</span><span class="n">discriminator</span> <span class="o">=</span> <span class="n">discriminator</span> <span class="k">class</span> <span class="nc">Customer</span><span class="p">(</span><span class="n">HasAddresses</span><span class="p">,</span> <span class="n">Base</span><span class="p">):</span> <span class="n">name</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">Supplier</span><span class="p">(</span><span class="n">HasAddresses</span><span class="p">,</span> <span class="n">Base</span><span class="p">):</span> <span class="n">company_name</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="n">engine</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">engine</span><span class="p">)</span> <span class="n">session</span> <span class="o">=</span> <span class="n">Session</span><span class="p">(</span><span class="n">engine</span><span class="p">)</span> <span class="n">session</span><span class="o">.</span><span class="n">add_all</span><span class="p">(</span> <span class="p">[</span> <span class="n">Customer</span><span class="p">(</span> <span class="n">name</span><span class="o">=</span><span class="s2">"customer 1"</span><span class="p">,</span> <span class="n">addresses</span><span class="o">=</span><span class="p">[</span> <span class="n">Address</span><span class="p">(</span> <span class="n">street</span><span class="o">=</span><span class="s2">"123 anywhere street"</span><span class="p">,</span> <span class="n">city</span><span class="o">=</span><span class="s2">"New York"</span><span class="p">,</span> <span class="nb">zip</span><span class="o">=</span><span class="s2">"10110"</span> <span class="p">),</span> <span class="n">Address</span><span class="p">(</span> <span class="n">street</span><span class="o">=</span><span class="s2">"40 main street"</span><span class="p">,</span> <span class="n">city</span><span class="o">=</span><span class="s2">"San Francisco"</span><span class="p">,</span> <span class="nb">zip</span><span class="o">=</span><span class="s2">"95732"</span> <span class="p">),</span> <span class="p">],</span> <span class="p">),</span> <span class="n">Supplier</span><span class="p">(</span> <span class="n">company_name</span><span class="o">=</span><span class="s2">"Ace Hammers"</span><span class="p">,</span> <span class="n">addresses</span><span class="o">=</span><span class="p">[</span> <span class="n">Address</span><span class="p">(</span><span class="n">street</span><span class="o">=</span><span class="s2">"2569 west elm"</span><span class="p">,</span> <span class="n">city</span><span class="o">=</span><span class="s2">"Detroit"</span><span class="p">,</span> <span class="nb">zip</span><span class="o">=</span><span class="s2">"56785"</span><span class="p">)</span> <span class="p">],</span> <span class="p">),</span> <span class="p">]</span> <span class="p">)</span> <span class="n">session</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span> <span class="k">for</span> <span class="n">customer</span> <span class="ow">in</span> <span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Customer</span><span class="p">):</span> <span class="k">for</span> <span class="n">address</span> <span class="ow">in</span> <span class="n">customer</span><span class="o">.</span><span class="n">addresses</span><span class="p">:</span> <span class="nb">print</span><span class="p">(</span><span class="n">address</span><span class="p">)</span> <span class="nb">print</span><span class="p">(</span><span class="n">address</span><span class="o">.</span><span class="n">parent</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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