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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.versioned_rows.versioned_rows_w_versionid</h1><div class="highlight"><pre>
<span></span><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">This example adds a numerical version_id to the Versioned class as well</span>
<span class="sd">as the ability to see which row is the most "current" vesion.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">Boolean</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">event</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">ForeignKeyConstraint</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">func</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">select</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.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">attributes</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">backref</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">column_property</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">make_transient</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</span> <span class="k">import</span> <span class="n">sessionmaker</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="c1"># we have a composite primary key consisting of "id"</span>
<span class="c1"># and "version_id"</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">version_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">default</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="c1"># optional - add a persisted is_current_version column</span>
<span class="n">is_current_version</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Boolean</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="c1"># optional - add a calculated is_current_version column</span>
<span class="nd">@classmethod</span>
<span class="k">def</span> <span class="nf">__declare_last__</span><span class="p">(</span><span class="bp">cls</span><span class="p">):</span>
<span class="n">alias</span> <span class="o">=</span> <span class="bp">cls</span><span class="o">.</span><span class="n">__table__</span><span class="o">.</span><span class="n">alias</span><span class="p">()</span>
<span class="bp">cls</span><span class="o">.</span><span class="n">calc_is_current_version</span> <span class="o">=</span> <span class="n">column_property</span><span class="p">(</span>
<span class="n">select</span><span class="p">([</span><span class="n">func</span><span class="o">.</span><span class="n">max</span><span class="p">(</span><span class="n">alias</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">version_id</span><span class="p">)</span> <span class="o">==</span> <span class="bp">cls</span><span class="o">.</span><span class="n">version_id</span><span class="p">])</span><span class="o">.</span><span class="n">where</span><span class="p">(</span>
<span class="n">alias</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">id</span> <span class="o">==</span> <span class="bp">cls</span><span class="o">.</span><span class="n">id</span>
<span class="p">)</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="c1"># optional - set previous version to have is_current_version=False</span>
<span class="n">old_id</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">id</span>
<span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span><span class="p">)</span><span class="o">.</span><span class="n">filter_by</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="n">old_id</span><span class="p">)</span><span class="o">.</span><span class="n">update</span><span class="p">(</span>
<span class="n">values</span><span class="o">=</span><span class="nb">dict</span><span class="p">(</span><span class="n">is_current_version</span><span class="o">=</span><span class="kc">False</span><span class="p">),</span> <span class="n">synchronize_session</span><span class="o">=</span><span class="kc">False</span>
<span class="p">)</span>
<span class="c1"># make us transient (removes persistent</span>
<span class="c1"># identity).</span>
<span class="n">make_transient</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
<span class="c1"># increment version_id, which means we have a new PK.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">version_id</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="nd">@event</span><span class="o">.</span><span class="n">listens_for</span><span class="p">(</span><span class="n">Session</span><span class="p">,</span> <span class="s2">"before_flush"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">before_flush</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="kc">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="c1"># 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="c1"># 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="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">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="c1"># 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="s2">"example"</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">data</span><span class="o">=</span><span class="s2">"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="s2">"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">version_id</span><span class="p">,</span>
<span class="n">Example</span><span class="o">.</span><span class="n">is_current_version</span><span class="p">,</span>
<span class="n">Example</span><span class="o">.</span><span class="n">calc_is_current_version</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="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="n">Example</span><span class="o">.</span><span class="n">version_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="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="kc">False</span><span class="p">,</span> <span class="kc">False</span><span class="p">,</span> <span class="s2">"e1"</span><span class="p">),</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="kc">True</span><span class="p">,</span> <span class="kc">True</span><span class="p">,</span> <span class="s2">"e2"</span><span class="p">)]</span>
<span class="p">)</span>
<span class="c1"># 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="s2">"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="kc">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">child_version_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">child</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"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="s2">"parent"</span><span class="p">,</span> <span class="n">uselist</span><span class="o">=</span><span class="kc">False</span><span class="p">))</span>
<span class="n">__table_args__</span> <span class="o">=</span> <span class="p">(</span>
<span class="n">ForeignKeyConstraint</span><span class="p">(</span>
<span class="p">[</span><span class="s2">"child_id"</span><span class="p">,</span> <span class="s2">"child_version_id"</span><span class="p">],</span> <span class="p">[</span><span class="s2">"child.id"</span><span class="p">,</span> <span class="s2">"child.version_id"</span><span class="p">]</span>
<span class="p">),</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="s2">"child"</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="c1"># 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="s2">"child"</span><span class="p">])</span>
<span class="c1"># 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="c1"># re-add ourselves to the parent. this causes the</span>
<span class="c1"># parent foreign key to be updated also</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">data</span><span class="o">=</span><span class="s2">"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="s2">"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">1</span>
<span class="k">assert</span> <span class="n">p1</span><span class="o">.</span><span class="n">child</span><span class="o">.</span><span class="n">version_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">version_id</span><span class="p">,</span>
<span class="n">Child</span><span class="o">.</span><span class="n">is_current_version</span><span class="p">,</span>
<span class="n">Child</span><span class="o">.</span><span class="n">calc_is_current_version</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="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="n">Child</span><span class="o">.</span><span class="n">version_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="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="kc">False</span><span class="p">,</span> <span class="kc">False</span><span class="p">,</span> <span class="s2">"c1"</span><span class="p">),</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="kc">True</span><span class="p">,</span> <span class="kc">True</span><span class="p">,</span> <span class="s2">"c2"</span><span class="p">)]</span>
<span class="p">)</span></pre></div>
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distrib
>
Mageia
>
7
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
b0b6ffab06cbeede296e36ce94734bf8
>
files
>
703
