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        Release: <span class="version-num">0.9.8</span> | Release Date: October 13, 2014
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<h1>Source code for examples.generic_associations.discriminator_on_association</h1><div class="highlight"><pre>
<span class="sd">&quot;&quot;&quot;discriminator_on_related.py</span>

<span class="sd">Illustrates a mixin which provides a generic association</span>
<span class="sd">using a single target table and a single association table,</span>
<span class="sd">referred to by all parent tables.  The association table</span>
<span class="sd">contains a &quot;discriminator&quot; column which determines what type of</span>
<span class="sd">parent object associates to each particular row in the association</span>
<span class="sd">table.</span>

<span class="sd">SQLAlchemy&#39;s single-table-inheritance feature is used</span>
<span class="sd">to target different association types.</span>

<span class="sd">This configuration attempts to simulate a so-called &quot;generic foreign key&quot;</span>
<span class="sd">as closely as possible without actually foregoing the use of real</span>
<span class="sd">foreign keys.   Unlike table-per-related and table-per-association,</span>
<span class="sd">it uses a fixed number of tables to serve any number of potential parent</span>
<span class="sd">objects, but is also slightly more complex.</span>

<span class="sd">&quot;&quot;&quot;</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.ext.declarative</span> <span class="kn">import</span> <span class="n">as_declarative</span><span class="p">,</span> <span class="n">declared_attr</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="kn">import</span> <span class="n">create_engine</span><span class="p">,</span> <span class="n">Integer</span><span class="p">,</span> <span class="n">Column</span><span class="p">,</span> \
                    <span class="n">String</span><span class="p">,</span> <span class="n">ForeignKey</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="n">Session</span><span class="p">,</span> <span class="n">relationship</span><span class="p">,</span> <span class="n">backref</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.ext.associationproxy</span> <span class="kn">import</span> <span class="n">association_proxy</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">&quot;&quot;&quot;Base class which provides automated table name</span>
<span class="sd">    and surrogate primary key column.</span>

<span class="sd">    &quot;&quot;&quot;</span>
    <span class="nd">@declared_attr</span>
    <span class="k">def</span> <span class="nf">__tablename__</span><span class="p">(</span><span class="n">cls</span><span class="p">):</span>
        <span class="k">return</span> <span class="n">cls</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="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="k">class</span> <span class="nc">AddressAssociation</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
    <span class="sd">&quot;&quot;&quot;Associates a collection of Address objects</span>
<span class="sd">    with a particular parent.</span>

<span class="sd">    &quot;&quot;&quot;</span>
    <span class="n">__tablename__</span> <span class="o">=</span> <span class="s">&quot;address_association&quot;</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">&quot;&quot;&quot;Refers to the type of parent.&quot;&quot;&quot;</span>

    <span class="n">__mapper_args__</span> <span class="o">=</span> <span class="p">{</span><span class="s">&quot;polymorphic_on&quot;</span><span class="p">:</span> <span class="n">discriminator</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">&quot;&quot;&quot;The Address class.</span>

<span class="sd">    This represents all address records in a</span>
<span class="sd">    single table.</span>

<span class="sd">    &quot;&quot;&quot;</span>
    <span class="n">association_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">ForeignKey</span><span class="p">(</span><span class="s">&quot;address_association.id&quot;</span><span class="p">))</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">association</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s">&quot;AddressAssociation&quot;</span><span class="p">,</span> <span class="n">backref</span><span class="o">=</span><span class="s">&quot;addresses&quot;</span><span class="p">)</span>

    <span class="n">parent</span> <span class="o">=</span> <span class="n">association_proxy</span><span class="p">(</span><span class="s">&quot;association&quot;</span><span class="p">,</span> <span class="s">&quot;parent&quot;</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="s">&quot;</span><span class="si">%s</span><span class="s">(street=</span><span class="si">%r</span><span class="s">, city=</span><span class="si">%r</span><span class="s">, zip=</span><span class="si">%r</span><span class="s">)&quot;</span> <span class="o">%</span> \
            <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">__class__</span><span class="o">.</span><span class="n">__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="k">class</span> <span class="nc">HasAddresses</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="sd">&quot;&quot;&quot;HasAddresses mixin, creates a relationship to</span>
<span class="sd">    the address_association table for each parent.</span>

<span class="sd">    &quot;&quot;&quot;</span>
    <span class="nd">@declared_attr</span>
    <span class="k">def</span> <span class="nf">address_association_id</span><span class="p">(</span><span class="n">cls</span><span class="p">):</span>
        <span class="k">return</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">ForeignKey</span><span class="p">(</span><span class="s">&quot;address_association.id&quot;</span><span class="p">))</span>

    <span class="nd">@declared_attr</span>
    <span class="k">def</span> <span class="nf">address_association</span><span class="p">(</span><span class="n">cls</span><span class="p">):</span>
        <span class="n">name</span> <span class="o">=</span> <span class="n">cls</span><span class="o">.</span><span class="n">__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">assoc_cls</span> <span class="o">=</span> <span class="nb">type</span><span class="p">(</span>
                        <span class="s">&quot;</span><span class="si">%s</span><span class="s">AddressAssociation&quot;</span> <span class="o">%</span> <span class="n">name</span><span class="p">,</span>
                        <span class="p">(</span><span class="n">AddressAssociation</span><span class="p">,</span> <span class="p">),</span>
                        <span class="nb">dict</span><span class="p">(</span>
                            <span class="n">__mapper_args__</span><span class="o">=</span><span class="p">{</span>
                                <span class="s">&quot;polymorphic_identity&quot;</span><span class="p">:</span> <span class="n">discriminator</span>
                            <span class="p">}</span>
                        <span class="p">)</span>
                    <span class="p">)</span>

        <span class="n">cls</span><span class="o">.</span><span class="n">addresses</span> <span class="o">=</span> <span class="n">association_proxy</span><span class="p">(</span>
                    <span class="s">&quot;address_association&quot;</span><span class="p">,</span> <span class="s">&quot;addresses&quot;</span><span class="p">,</span>
                    <span class="n">creator</span><span class="o">=</span><span class="k">lambda</span> <span class="n">addresses</span><span class="p">:</span> <span class="n">assoc_cls</span><span class="p">(</span><span class="n">addresses</span><span class="o">=</span><span class="n">addresses</span><span class="p">)</span>
                <span class="p">)</span>
        <span class="k">return</span> <span class="n">relationship</span><span class="p">(</span><span class="n">assoc_cls</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="s">&quot;parent&quot;</span><span class="p">,</span> <span class="n">uselist</span><span class="o">=</span><span class="bp">False</span><span class="p">))</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="s">&#39;sqlite://&#39;</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">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="n">Customer</span><span class="p">(</span>
        <span class="n">name</span><span class="o">=</span><span class="s">&#39;customer 1&#39;</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="s">&#39;123 anywhere street&#39;</span><span class="p">,</span>
                    <span class="n">city</span><span class="o">=</span><span class="s">&quot;New York&quot;</span><span class="p">,</span>
                    <span class="nb">zip</span><span class="o">=</span><span class="s">&quot;10110&quot;</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="s">&#39;40 main street&#39;</span><span class="p">,</span>
                    <span class="n">city</span><span class="o">=</span><span class="s">&quot;San Francisco&quot;</span><span class="p">,</span>
                    <span class="nb">zip</span><span class="o">=</span><span class="s">&quot;95732&quot;</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="s">&quot;Ace Hammers&quot;</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="s">&#39;2569 west elm&#39;</span><span class="p">,</span>
                    <span class="n">city</span><span class="o">=</span><span class="s">&quot;Detroit&quot;</span><span class="p">,</span>
                    <span class="nb">zip</span><span class="o">=</span><span class="s">&quot;56785&quot;</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="k">print</span><span class="p">(</span><span class="n">address</span><span class="p">)</span>
        <span class="k">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>
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