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examples.custom_attributes.custom_management
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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.custom_attributes.custom_management</h1><div class="highlight"><pre>
<span></span><span class="sd">"""Illustrates customized class instrumentation, using</span>
<span class="sd">the :mod:`sqlalchemy.ext.instrumentation` extension package.</span>
<span class="sd">In this example, mapped classes are modified to</span>
<span class="sd">store their state in a dictionary attached to an attribute</span>
<span class="sd">named "_goofy_dict", instead of using __dict__.</span>
<span class="sd">this example illustrates how to replace SQLAlchemy's class</span>
<span class="sd">descriptors with a user-defined system.</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">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">MetaData</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">Table</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">Text</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.ext.instrumentation</span> <span class="k">import</span> <span class="n">InstrumentationManager</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">mapper</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.attributes</span> <span class="k">import</span> <span class="n">del_attribute</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm.attributes</span> <span class="k">import</span> <span class="n">get_attribute</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm.attributes</span> <span class="k">import</span> <span class="n">set_attribute</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm.instrumentation</span> <span class="k">import</span> <span class="n">is_instrumented</span>
<span class="k">class</span> <span class="nc">MyClassState</span><span class="p">(</span><span class="n">InstrumentationManager</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">get_instance_dict</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">class_</span><span class="p">,</span> <span class="n">instance</span><span class="p">):</span>
<span class="k">return</span> <span class="n">instance</span><span class="o">.</span><span class="n">_goofy_dict</span>
<span class="k">def</span> <span class="nf">initialize_instance_dict</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">class_</span><span class="p">,</span> <span class="n">instance</span><span class="p">):</span>
<span class="n">instance</span><span class="o">.</span><span class="vm">__dict__</span><span class="p">[</span><span class="s2">"_goofy_dict"</span><span class="p">]</span> <span class="o">=</span> <span class="p">{}</span>
<span class="k">def</span> <span class="nf">install_state</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">class_</span><span class="p">,</span> <span class="n">instance</span><span class="p">,</span> <span class="n">state</span><span class="p">):</span>
<span class="n">instance</span><span class="o">.</span><span class="vm">__dict__</span><span class="p">[</span><span class="s2">"_goofy_dict"</span><span class="p">][</span><span class="s2">"state"</span><span class="p">]</span> <span class="o">=</span> <span class="n">state</span>
<span class="k">def</span> <span class="nf">state_getter</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">class_</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">find</span><span class="p">(</span><span class="n">instance</span><span class="p">):</span>
<span class="k">return</span> <span class="n">instance</span><span class="o">.</span><span class="vm">__dict__</span><span class="p">[</span><span class="s2">"_goofy_dict"</span><span class="p">][</span><span class="s2">"state"</span><span class="p">]</span>
<span class="k">return</span> <span class="n">find</span>
<span class="k">class</span> <span class="nc">MyClass</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="n">__sa_instrumentation_manager__</span> <span class="o">=</span> <span class="n">MyClassState</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="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="k">for</span> <span class="n">k</span> <span class="ow">in</span> <span class="n">kwargs</span><span class="p">:</span>
<span class="nb">setattr</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">k</span><span class="p">,</span> <span class="n">kwargs</span><span class="p">[</span><span class="n">k</span><span class="p">])</span>
<span class="k">def</span> <span class="nf">__getattr__</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">if</span> <span class="n">is_instrumented</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">get_attribute</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">else</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_goofy_dict</span><span class="p">[</span><span class="n">key</span><span class="p">]</span>
<span class="k">except</span> <span class="ne">KeyError</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">AttributeError</span><span class="p">(</span><span class="n">key</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__setattr__</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">if</span> <span class="n">is_instrumented</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">set_attribute</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">else</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_goofy_dict</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">__delattr__</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">if</span> <span class="n">is_instrumented</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">del_attribute</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">else</span><span class="p">:</span>
<span class="k">del</span> <span class="bp">self</span><span class="o">.</span><span class="n">_goofy_dict</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="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">meta</span> <span class="o">=</span> <span class="n">MetaData</span><span class="p">()</span>
<span class="n">table1</span> <span class="o">=</span> <span class="n">Table</span><span class="p">(</span>
<span class="s2">"table1"</span><span class="p">,</span>
<span class="n">meta</span><span class="p">,</span>
<span class="n">Column</span><span class="p">(</span><span class="s2">"id"</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">Column</span><span class="p">(</span><span class="s2">"name"</span><span class="p">,</span> <span class="n">Text</span><span class="p">),</span>
<span class="p">)</span>
<span class="n">table2</span> <span class="o">=</span> <span class="n">Table</span><span class="p">(</span>
<span class="s2">"table2"</span><span class="p">,</span>
<span class="n">meta</span><span class="p">,</span>
<span class="n">Column</span><span class="p">(</span><span class="s2">"id"</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">Column</span><span class="p">(</span><span class="s2">"name"</span><span class="p">,</span> <span class="n">Text</span><span class="p">),</span>
<span class="n">Column</span><span class="p">(</span><span class="s2">"t1id"</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">"table1.id"</span><span class="p">)),</span>
<span class="p">)</span>
<span class="n">meta</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="k">class</span> <span class="nc">A</span><span class="p">(</span><span class="n">MyClass</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">class</span> <span class="nc">B</span><span class="p">(</span><span class="n">MyClass</span><span class="p">):</span>
<span class="k">pass</span>
<span class="n">mapper</span><span class="p">(</span><span class="n">A</span><span class="p">,</span> <span class="n">table1</span><span class="p">,</span> <span class="n">properties</span><span class="o">=</span><span class="p">{</span><span class="s2">"bs"</span><span class="p">:</span> <span class="n">relationship</span><span class="p">(</span><span class="n">B</span><span class="p">)})</span>
<span class="n">mapper</span><span class="p">(</span><span class="n">B</span><span class="p">,</span> <span class="n">table2</span><span class="p">)</span>
<span class="n">a1</span> <span class="o">=</span> <span class="n">A</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s2">"a1"</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">name</span><span class="o">=</span><span class="s2">"b1"</span><span class="p">),</span> <span class="n">B</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s2">"b2"</span><span class="p">)])</span>
<span class="k">assert</span> <span class="n">a1</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="s2">"a1"</span>
<span class="k">assert</span> <span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="s2">"b1"</span>
<span class="n">sess</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">sess</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">a1</span><span class="p">)</span>
<span class="n">sess</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">sess</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">get</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">id</span><span class="p">)</span>
<span class="k">assert</span> <span class="n">a1</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="s2">"a1"</span>
<span class="k">assert</span> <span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="s2">"b1"</span>
<span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="n">sess</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">sess</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">get</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">id</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">a1</span><span class="o">.</span><span class="n">bs</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1</span></pre></div>
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