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examples.association.dict_of_sets_with_default
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SQLAlchemy 1.2 Documentation
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Release: <span class="version-num">1.2.19</span>
| Release Date: April 15, 2019
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<h1>SQLAlchemy 1.2 Documentation</h1>
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<h1>Source code for examples.association.dict_of_sets_with_default</h1><div class="highlight"><pre>
<span></span><span class="sd">"""An advanced association proxy example which</span>
<span class="sd">illustrates nesting of association proxies to produce multi-level Python</span>
<span class="sd">collections, in this case a dictionary with string keys and sets of integers</span>
<span class="sd">as values, which conceal the underlying mapped classes.</span>
<span class="sd">This is a three table model which represents a parent table referencing a</span>
<span class="sd">dictionary of string keys and sets as values, where each set stores a</span>
<span class="sd">collection of integers. The association proxy extension is used to hide the</span>
<span class="sd">details of this persistence. The dictionary also generates new collections</span>
<span class="sd">upon access of a non-existent key, in the same manner as Python's</span>
<span class="sd">"collections.defaultdict" object.</span>
<span class="sd">"""</span>
<span class="kn">import</span> <span class="nn">operator</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">ForeignKey</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.associationproxy</span> <span class="k">import</span> <span class="n">association_proxy</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="kn">from</span> <span class="nn">sqlalchemy.orm.collections</span> <span class="k">import</span> <span class="n">MappedCollection</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="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">Base</span> <span class="o">=</span> <span class="n">declarative_base</span><span class="p">(</span><span class="bp">cls</span><span class="o">=</span><span class="n">Base</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">GenDefaultCollection</span><span class="p">(</span><span class="n">MappedCollection</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__missing__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">key</span><span class="p">):</span>
<span class="bp">self</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">b</span> <span class="o">=</span> <span class="n">B</span><span class="p">(</span><span class="n">key</span><span class="p">)</span>
<span class="k">return</span> <span class="n">b</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="n">__tablename__</span> <span class="o">=</span> <span class="s2">"a"</span>
<span class="n">associations</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span>
<span class="s2">"B"</span><span class="p">,</span>
<span class="n">collection_class</span><span class="o">=</span><span class="k">lambda</span><span class="p">:</span> <span class="n">GenDefaultCollection</span><span class="p">(</span>
<span class="n">operator</span><span class="o">.</span><span class="n">attrgetter</span><span class="p">(</span><span class="s2">"key"</span><span class="p">)</span>
<span class="p">),</span>
<span class="p">)</span>
<span class="n">collections</span> <span class="o">=</span> <span class="n">association_proxy</span><span class="p">(</span><span class="s2">"associations"</span><span class="p">,</span> <span class="s2">"values"</span><span class="p">)</span>
<span class="sd">"""Bridge the association from 'associations' over to the 'values'</span>
<span class="sd"> association proxy of B.</span>
<span class="sd"> """</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="n">__tablename__</span> <span class="o">=</span> <span class="s2">"b"</span>
<span class="n">a_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="s2">"a.id"</span><span class="p">),</span> <span class="n">nullable</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="n">elements</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"C"</span><span class="p">,</span> <span class="n">collection_class</span><span class="o">=</span><span class="nb">set</span><span class="p">)</span>
<span class="n">key</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">values</span> <span class="o">=</span> <span class="n">association_proxy</span><span class="p">(</span><span class="s2">"elements"</span><span class="p">,</span> <span class="s2">"value"</span><span class="p">)</span>
<span class="sd">"""Bridge the association from 'elements' over to the</span>
<span class="sd"> 'value' element of C."""</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">key</span><span class="p">,</span> <span class="n">values</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">key</span> <span class="o">=</span> <span class="n">key</span>
<span class="k">if</span> <span class="n">values</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">values</span> <span class="o">=</span> <span class="n">values</span>
<span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s2">"c"</span>
<span class="n">b_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="s2">"b.id"</span><span class="p">),</span> <span class="n">nullable</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="n">value</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="k">def</span> <span class="nf">__init__</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="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">=</span> <span class="n">value</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s2">"__main__"</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="c1"># only "A" is referenced explicitly. Using "collections",</span>
<span class="c1"># we deal with a dict of key/sets of integers directly.</span>
<span class="n">session</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">collections</span><span class="o">=</span><span class="p">{</span><span class="s2">"1"</span><span class="p">:</span> <span class="nb">set</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</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="n">a1</span> <span class="o">=</span> <span class="n">session</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">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">collections</span><span class="p">[</span><span class="s2">"1"</span><span class="p">])</span>
<span class="n">a1</span><span class="o">.</span><span class="n">collections</span><span class="p">[</span><span class="s2">"1"</span><span class="p">]</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="mi">4</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="n">a1</span><span class="o">.</span><span class="n">collections</span><span class="p">[</span><span class="s2">"2"</span><span class="p">]</span><span class="o">.</span><span class="n">update</span><span class="p">([</span><span class="mi">7</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">9</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="nb">print</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">collections</span><span class="p">[</span><span class="s2">"2"</span><span class="p">])</span></pre></div>
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