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examples.versioned_rows.versioned_rows
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Release: <span class="version-num">0.9.8</span> | Release Date: October 13, 2014
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<h1>SQLAlchemy 0.9 Documentation</h1>
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<h1>Source code for examples.versioned_rows.versioned_rows</h1><div class="highlight"><pre>
<span class="sd">"""Illustrates a method to intercept changes on objects, turning</span>
<span class="sd">an UPDATE statement on a single row into an INSERT statement, so that a new</span>
<span class="sd">row is inserted with the new data, keeping the old row intact.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm.interfaces</span> <span class="kn">import</span> <span class="n">SessionExtension</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.ext.declarative</span> <span class="kn">import</span> <span class="n">declarative_base</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="n">attributes</span>
<span class="k">class</span> <span class="nc">Versioned</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">new_version</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">session</span><span class="p">):</span>
<span class="c"># if on SQLA 0.6.1 or earlier,</span>
<span class="c"># make sure 'id' isn't expired.</span>
<span class="c"># self.id</span>
<span class="c"># make us transient (removes persistent</span>
<span class="c"># identity).</span>
<span class="n">make_transient</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
<span class="c"># set 'id' to None.</span>
<span class="c"># a new PK will be generated on INSERT.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">id</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">class</span> <span class="nc">VersionExtension</span><span class="p">(</span><span class="n">SessionExtension</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">before_flush</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">session</span><span class="p">,</span> <span class="n">flush_context</span><span class="p">,</span> <span class="n">instances</span><span class="p">):</span>
<span class="k">for</span> <span class="n">instance</span> <span class="ow">in</span> <span class="n">session</span><span class="o">.</span><span class="n">dirty</span><span class="p">:</span>
<span class="k">if</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">instance</span><span class="p">,</span> <span class="n">Versioned</span><span class="p">):</span>
<span class="k">continue</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">session</span><span class="o">.</span><span class="n">is_modified</span><span class="p">(</span><span class="n">instance</span><span class="p">,</span> <span class="n">passive</span><span class="o">=</span><span class="bp">True</span><span class="p">):</span>
<span class="k">continue</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">attributes</span><span class="o">.</span><span class="n">instance_state</span><span class="p">(</span><span class="n">instance</span><span class="p">)</span><span class="o">.</span><span class="n">has_identity</span><span class="p">:</span>
<span class="k">continue</span>
<span class="c"># make it transient</span>
<span class="n">instance</span><span class="o">.</span><span class="n">new_version</span><span class="p">(</span><span class="n">session</span><span class="p">)</span>
<span class="c"># re-add</span>
<span class="n">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">instance</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="n">engine</span> <span class="o">=</span> <span class="n">create_engine</span><span class="p">(</span><span class="s">'sqlite://'</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">Session</span> <span class="o">=</span> <span class="n">sessionmaker</span><span class="p">(</span><span class="n">engine</span><span class="p">,</span> <span class="n">extension</span><span class="o">=</span><span class="p">[</span><span class="n">VersionExtension</span><span class="p">()])</span>
<span class="c"># example 1, simple versioning</span>
<span class="k">class</span> <span class="nc">Example</span><span class="p">(</span><span class="n">Versioned</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="s">'example'</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="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="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">e1</span> <span class="o">=</span> <span class="n">Example</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="s">'e1'</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">e1</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">e1</span><span class="o">.</span><span class="n">data</span> <span class="o">=</span> <span class="s">'e2'</span>
<span class="n">session</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span>
<span class="k">assert</span> <span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Example</span><span class="o">.</span><span class="n">id</span><span class="p">,</span> <span class="n">Example</span><span class="o">.</span><span class="n">data</span><span class="p">)</span><span class="o">.</span><span class="n">order_by</span><span class="p">(</span><span class="n">Example</span><span class="o">.</span><span class="n">id</span><span class="p">)</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="o">==</span> \
<span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="s">'e1'</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s">'e2'</span><span class="p">)]</span>
<span class="c"># example 2, versioning with a parent</span>
<span class="k">class</span> <span class="nc">Parent</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="s">'parent'</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="n">child_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">'child.id'</span><span class="p">))</span>
<span class="n">child</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s">"Child"</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">'parent'</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">Child</span><span class="p">(</span><span class="n">Versioned</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="s">'child'</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="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="k">def</span> <span class="nf">new_version</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">session</span><span class="p">):</span>
<span class="c"># expire parent's reference to us</span>
<span class="n">session</span><span class="o">.</span><span class="n">expire</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">parent</span><span class="p">,</span> <span class="p">[</span><span class="s">'child'</span><span class="p">])</span>
<span class="c"># create new version</span>
<span class="n">Versioned</span><span class="o">.</span><span class="n">new_version</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">session</span><span class="p">)</span>
<span class="c"># re-add ourselves to the parent</span>
<span class="bp">self</span><span class="o">.</span><span class="n">parent</span><span class="o">.</span><span class="n">child</span> <span class="o">=</span> <span class="bp">self</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">p1</span> <span class="o">=</span> <span class="n">Parent</span><span class="p">(</span><span class="n">child</span><span class="o">=</span><span class="n">Child</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="s">'c1'</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">p1</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">p1</span><span class="o">.</span><span class="n">child</span><span class="o">.</span><span class="n">data</span> <span class="o">=</span> <span class="s">'c2'</span>
<span class="n">session</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span>
<span class="k">assert</span> <span class="n">p1</span><span class="o">.</span><span class="n">child_id</span> <span class="o">==</span> <span class="mi">2</span>
<span class="k">assert</span> <span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Child</span><span class="o">.</span><span class="n">id</span><span class="p">,</span> <span class="n">Child</span><span class="o">.</span><span class="n">data</span><span class="p">)</span><span class="o">.</span><span class="n">order_by</span><span class="p">(</span><span class="n">Child</span><span class="o">.</span><span class="n">id</span><span class="p">)</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="o">==</span> \
<span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="s">'c1'</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s">'c2'</span><span class="p">)]</span></pre></div>
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