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examples.vertical.dictlike
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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.vertical.dictlike</h1><div class="highlight"><pre>
<span></span><span class="sd">"""Mapping a vertical table as a dictionary.</span>
<span class="sd">This example illustrates accessing and modifying a "vertical" (or</span>
<span class="sd">"properties", or pivoted) table via a dict-like interface. These are tables</span>
<span class="sd">that store free-form object properties as rows instead of columns. For</span>
<span class="sd">example, instead of::</span>
<span class="sd"> # A regular ("horizontal") table has columns for 'species' and 'size'</span>
<span class="sd"> Table('animal', metadata,</span>
<span class="sd"> Column('id', Integer, primary_key=True),</span>
<span class="sd"> Column('species', Unicode),</span>
<span class="sd"> Column('size', Unicode))</span>
<span class="sd">A vertical table models this as two tables: one table for the base or parent</span>
<span class="sd">entity, and another related table holding key/value pairs::</span>
<span class="sd"> Table('animal', metadata,</span>
<span class="sd"> Column('id', Integer, primary_key=True))</span>
<span class="sd"> # The properties table will have one row for a 'species' value, and</span>
<span class="sd"> # another row for the 'size' value.</span>
<span class="sd"> Table('properties', metadata</span>
<span class="sd"> Column('animal_id', Integer, ForeignKey('animal.id'),</span>
<span class="sd"> primary_key=True),</span>
<span class="sd"> Column('key', UnicodeText),</span>
<span class="sd"> Column('value', UnicodeText))</span>
<span class="sd">Because the key/value pairs in a vertical scheme are not fixed in advance,</span>
<span class="sd">accessing them like a Python dict can be very convenient. The example below</span>
<span class="sd">can be used with many common vertical schemas as-is or with minor adaptations.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">unicode_literals</span>
<span class="k">class</span> <span class="nc">ProxiedDictMixin</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""Adds obj[key] access to a mapped class.</span>
<span class="sd"> This class basically proxies dictionary access to an attribute</span>
<span class="sd"> called ``_proxied``. The class which inherits this class</span>
<span class="sd"> should have an attribute called ``_proxied`` which points to a dictionary.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__len__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">iter</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__getitem__</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="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span><span class="p">[</span><span class="n">key</span><span class="p">]</span>
<span class="k">def</span> <span class="nf">__contains__</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="k">return</span> <span class="n">key</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span>
<span class="k">def</span> <span class="nf">__setitem__</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">value</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">value</span>
<span class="k">def</span> <span class="nf">__delitem__</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="k">del</span> <span class="bp">self</span><span class="o">.</span><span class="n">_proxied</span><span class="p">[</span><span class="n">key</span><span class="p">]</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="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="p">(</span>
<span class="n">Column</span><span class="p">,</span>
<span class="n">Integer</span><span class="p">,</span>
<span class="n">Unicode</span><span class="p">,</span>
<span class="n">ForeignKey</span><span class="p">,</span>
<span class="n">UnicodeText</span><span class="p">,</span>
<span class="n">and_</span><span class="p">,</span>
<span class="n">create_engine</span><span class="p">,</span>
<span class="p">)</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">relationship</span><span class="p">,</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">attribute_mapped_collection</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.ext.associationproxy</span> <span class="k">import</span> <span class="n">association_proxy</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">AnimalFact</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="sd">"""A fact about an animal."""</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s2">"animal_fact"</span>
<span class="n">animal_id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">ForeignKey</span><span class="p">(</span><span class="s2">"animal.id"</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">key</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Unicode</span><span class="p">(</span><span class="mi">64</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">value</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">UnicodeText</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Animal</span><span class="p">(</span><span class="n">ProxiedDictMixin</span><span class="p">,</span> <span class="n">Base</span><span class="p">):</span>
<span class="sd">"""an Animal"""</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s2">"animal"</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">name</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Unicode</span><span class="p">(</span><span class="mi">100</span><span class="p">))</span>
<span class="n">facts</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span>
<span class="s2">"AnimalFact"</span><span class="p">,</span> <span class="n">collection_class</span><span class="o">=</span><span class="n">attribute_mapped_collection</span><span class="p">(</span><span class="s2">"key"</span><span class="p">)</span>
<span class="p">)</span>
<span class="n">_proxied</span> <span class="o">=</span> <span class="n">association_proxy</span><span class="p">(</span>
<span class="s2">"facts"</span><span class="p">,</span>
<span class="s2">"value"</span><span class="p">,</span>
<span class="n">creator</span><span class="o">=</span><span class="k">lambda</span> <span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">:</span> <span class="n">AnimalFact</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="n">value</span><span class="p">),</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">name</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">name</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">"Animal(</span><span class="si">%r</span><span class="s2">)"</span> <span class="o">%</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span>
<span class="nd">@classmethod</span>
<span class="k">def</span> <span class="nf">with_characteristic</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">value</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">facts</span><span class="o">.</span><span class="n">any</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="n">value</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">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">bind</span><span class="o">=</span><span class="n">engine</span><span class="p">)</span>
<span class="n">stoat</span> <span class="o">=</span> <span class="n">Animal</span><span class="p">(</span><span class="s2">"stoat"</span><span class="p">)</span>
<span class="n">stoat</span><span class="p">[</span><span class="s2">"color"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"reddish"</span>
<span class="n">stoat</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"somewhat"</span>
<span class="c1"># dict-like assignment transparently creates entries in the</span>
<span class="c1"># stoat.facts collection:</span>
<span class="nb">print</span><span class="p">(</span><span class="n">stoat</span><span class="o">.</span><span class="n">facts</span><span class="p">[</span><span class="s2">"color"</span><span class="p">])</span>
<span class="n">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">stoat</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">critter</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">Animal</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">Animal</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="s2">"stoat"</span><span class="p">)</span><span class="o">.</span><span class="n">one</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="n">critter</span><span class="p">[</span><span class="s2">"color"</span><span class="p">])</span>
<span class="nb">print</span><span class="p">(</span><span class="n">critter</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">])</span>
<span class="n">critter</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"very"</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"changing cuteness:"</span><span class="p">)</span>
<span class="n">marten</span> <span class="o">=</span> <span class="n">Animal</span><span class="p">(</span><span class="s2">"marten"</span><span class="p">)</span>
<span class="n">marten</span><span class="p">[</span><span class="s2">"color"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"brown"</span>
<span class="n">marten</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"somewhat"</span>
<span class="n">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">marten</span><span class="p">)</span>
<span class="n">shrew</span> <span class="o">=</span> <span class="n">Animal</span><span class="p">(</span><span class="s2">"shrew"</span><span class="p">)</span>
<span class="n">shrew</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"somewhat"</span>
<span class="n">shrew</span><span class="p">[</span><span class="s2">"poisonous-part"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"saliva"</span>
<span class="n">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">shrew</span><span class="p">)</span>
<span class="n">loris</span> <span class="o">=</span> <span class="n">Animal</span><span class="p">(</span><span class="s2">"slow loris"</span><span class="p">)</span>
<span class="n">loris</span><span class="p">[</span><span class="s2">"cuteness"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"fairly"</span>
<span class="n">loris</span><span class="p">[</span><span class="s2">"poisonous-part"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"elbows"</span>
<span class="n">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">loris</span><span class="p">)</span>
<span class="n">q</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">Animal</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span>
<span class="n">Animal</span><span class="o">.</span><span class="n">facts</span><span class="o">.</span><span class="n">any</span><span class="p">(</span>
<span class="n">and_</span><span class="p">(</span><span class="n">AnimalFact</span><span class="o">.</span><span class="n">key</span> <span class="o">==</span> <span class="s2">"color"</span><span class="p">,</span> <span class="n">AnimalFact</span><span class="o">.</span><span class="n">value</span> <span class="o">==</span> <span class="s2">"reddish"</span><span class="p">)</span>
<span class="p">)</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"reddish animals"</span><span class="p">,</span> <span class="n">q</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="n">q</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">Animal</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span>
<span class="n">Animal</span><span class="o">.</span><span class="n">with_characteristic</span><span class="p">(</span><span class="s2">"color"</span><span class="p">,</span> <span class="s2">"brown"</span><span class="p">)</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"brown animals"</span><span class="p">,</span> <span class="n">q</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="n">q</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">Animal</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span>
<span class="o">~</span><span class="n">Animal</span><span class="o">.</span><span class="n">with_characteristic</span><span class="p">(</span><span class="s2">"poisonous-part"</span><span class="p">,</span> <span class="s2">"elbows"</span><span class="p">)</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"animals without poisonous-part == elbows"</span><span class="p">,</span> <span class="n">q</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="n">q</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">Animal</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">Animal</span><span class="o">.</span><span class="n">facts</span><span class="o">.</span><span class="n">any</span><span class="p">(</span><span class="n">value</span><span class="o">=</span><span class="s2">"somewhat"</span><span class="p">))</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'any animal with any .value of "somewhat"'</span><span class="p">,</span> <span class="n">q</span><span class="o">.</span><span class="n">all</span><span class="p">())</span></pre></div>
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