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examples.custom_attributes.listen_for_events
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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.listen_for_events</h1><div class="highlight"><pre>
<span></span><span class="sd">"""Illustrates how to attach events to all instrumented attributes</span>
<span class="sd">and listen for change events.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">event</span>
<span class="k">def</span> <span class="nf">configure_listener</span><span class="p">(</span><span class="n">class_</span><span class="p">,</span> <span class="n">key</span><span class="p">,</span> <span class="n">inst</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">append</span><span class="p">(</span><span class="n">instance</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">instance</span><span class="o">.</span><span class="n">receive_change_event</span><span class="p">(</span><span class="s2">"append"</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="kc">None</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">remove</span><span class="p">(</span><span class="n">instance</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">instance</span><span class="o">.</span><span class="n">receive_change_event</span><span class="p">(</span><span class="s2">"remove"</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="kc">None</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">set_</span><span class="p">(</span><span class="n">instance</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">oldvalue</span><span class="p">,</span> <span class="n">initiator</span><span class="p">):</span>
<span class="n">instance</span><span class="o">.</span><span class="n">receive_change_event</span><span class="p">(</span><span class="s2">"set"</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="n">oldvalue</span><span class="p">)</span>
<span class="n">event</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="n">inst</span><span class="p">,</span> <span class="s2">"append"</span><span class="p">,</span> <span class="n">append</span><span class="p">)</span>
<span class="n">event</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="n">inst</span><span class="p">,</span> <span class="s2">"remove"</span><span class="p">,</span> <span class="n">remove</span><span class="p">)</span>
<span class="n">event</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="n">inst</span><span class="p">,</span> <span class="s2">"set"</span><span class="p">,</span> <span class="n">set_</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="n">Column</span><span class="p">,</span> <span class="n">Integer</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="k">import</span> <span class="n">relationship</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="k">class</span> <span class="nc">Base</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">receive_change_event</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">verb</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="n">oldvalue</span><span class="p">):</span>
<span class="n">s</span> <span class="o">=</span> <span class="s2">"Value '</span><span class="si">%s</span><span class="s2">' </span><span class="si">%s</span><span class="s2"> on attribute '</span><span class="si">%s</span><span class="s2">', "</span> <span class="o">%</span> <span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">verb</span><span class="p">,</span> <span class="n">key</span><span class="p">)</span>
<span class="k">if</span> <span class="n">oldvalue</span><span class="p">:</span>
<span class="n">s</span> <span class="o">+=</span> <span class="s2">"which replaced the value '</span><span class="si">%s</span><span class="s2">', "</span> <span class="o">%</span> <span class="n">oldvalue</span>
<span class="n">s</span> <span class="o">+=</span> <span class="s2">"on object </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="bp">self</span>
<span class="nb">print</span><span class="p">(</span><span class="n">s</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="n">event</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="n">Base</span><span class="p">,</span> <span class="s2">"attribute_instrument"</span><span class="p">,</span> <span class="n">configure_listener</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">MyMappedClass</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">"mytable"</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">data</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="mi">50</span><span class="p">))</span>
<span class="n">related_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">"related.id"</span><span class="p">))</span>
<span class="n">related</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"Related"</span><span class="p">,</span> <span class="n">backref</span><span class="o">=</span><span class="s2">"mapped"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="s2">"MyMappedClass(data=</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">data</span>
<span class="k">class</span> <span class="nc">Related</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">"related"</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">data</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="mi">50</span><span class="p">))</span>
<span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="s2">"Related(data=</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">data</span>
<span class="c1"># classes are instrumented. Demonstrate the events !</span>
<span class="n">m1</span> <span class="o">=</span> <span class="n">MyMappedClass</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="s2">"m1"</span><span class="p">,</span> <span class="n">related</span><span class="o">=</span><span class="n">Related</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="s2">"r1"</span><span class="p">))</span>
<span class="n">m1</span><span class="o">.</span><span class="n">data</span> <span class="o">=</span> <span class="s2">"m1mod"</span>
<span class="n">m1</span><span class="o">.</span><span class="n">related</span><span class="o">.</span><span class="n">mapped</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">MyMappedClass</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="s2">"m2"</span><span class="p">))</span>
<span class="k">del</span> <span class="n">m1</span><span class="o">.</span><span class="n">data</span></pre></div>
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