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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.materialized_paths.materialized_paths</h1><div class="highlight"><pre>
<span class="sd">"""Illustrates the "materialized paths" pattern.</span>
<span class="sd">Materialized paths is a way to represent a tree structure in SQL with fast</span>
<span class="sd">descendant and ancestor queries at the expense of moving nodes (which require</span>
<span class="sd">O(n) UPDATEs in the worst case, where n is the number of nodes in the tree). It</span>
<span class="sd">is a good balance in terms of performance and simplicity between the nested</span>
<span class="sd">sets model and the adjacency list model.</span>
<span class="sd">It works by storing all nodes in a table with a path column, containing a</span>
<span class="sd">string of delimited IDs. Think file system paths:</span>
<span class="sd"> 1</span>
<span class="sd"> 1.2</span>
<span class="sd"> 1.3</span>
<span class="sd"> 1.3.4</span>
<span class="sd"> 1.3.5</span>
<span class="sd"> 1.3.6</span>
<span class="sd"> 1.7</span>
<span class="sd"> 1.7.8</span>
<span class="sd"> 1.7.9</span>
<span class="sd"> 1.7.9.10</span>
<span class="sd"> 1.7.11</span>
<span class="sd">Descendant queries are simple left-anchored LIKE queries, and ancestors are</span>
<span class="sd">already stored in the path itself. Updates require going through all</span>
<span class="sd">descendants and changing the prefix.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="kn">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">func</span><span class="p">,</span> <span class="n">select</span><span class="p">,</span> <span class="n">create_engine</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="n">remote</span><span class="p">,</span> <span class="n">foreign</span><span class="p">,</span> <span class="n">relationship</span><span class="p">,</span> <span class="n">Session</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.sql.expression</span> <span class="kn">import</span> <span class="n">cast</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.dialects.postgresql</span> <span class="kn">import</span> <span class="n">ARRAY</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">Node</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">"node"</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">autoincrement</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span>
<span class="n">path</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">500</span><span class="p">),</span> <span class="n">nullable</span><span class="o">=</span><span class="bp">False</span><span class="p">,</span> <span class="n">index</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="c"># To find the descendants of this node, we look for nodes whose path</span>
<span class="c"># starts with this node's path.</span>
<span class="n">descendants</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span>
<span class="s">"Node"</span><span class="p">,</span> <span class="n">viewonly</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">order_by</span><span class="o">=</span><span class="n">path</span><span class="p">,</span>
<span class="n">primaryjoin</span><span class="o">=</span><span class="n">remote</span><span class="p">(</span><span class="n">foreign</span><span class="p">(</span><span class="n">path</span><span class="p">))</span><span class="o">.</span><span class="n">like</span><span class="p">(</span><span class="n">path</span><span class="o">.</span><span class="n">concat</span><span class="p">(</span><span class="s">".%"</span><span class="p">)))</span>
<span class="c"># Finding the ancestors is a little bit trickier. We need to create a fake</span>
<span class="c"># secondary table since this behaves like a many-to-many join.</span>
<span class="n">secondary</span> <span class="o">=</span> <span class="n">select</span><span class="p">([</span>
<span class="nb">id</span><span class="o">.</span><span class="n">label</span><span class="p">(</span><span class="s">"id"</span><span class="p">),</span>
<span class="n">func</span><span class="o">.</span><span class="n">unnest</span><span class="p">(</span><span class="n">cast</span><span class="p">(</span><span class="n">func</span><span class="o">.</span><span class="n">string_to_array</span><span class="p">(</span>
<span class="n">func</span><span class="o">.</span><span class="n">regexp_replace</span><span class="p">(</span><span class="n">path</span><span class="p">,</span> <span class="s">r"\.?\d+$"</span><span class="p">,</span> <span class="s">""</span><span class="p">),</span> <span class="s">"."</span><span class="p">),</span>
<span class="n">ARRAY</span><span class="p">(</span><span class="n">Integer</span><span class="p">)))</span><span class="o">.</span><span class="n">label</span><span class="p">(</span><span class="s">"ancestor_id"</span><span class="p">)</span>
<span class="p">])</span><span class="o">.</span><span class="n">alias</span><span class="p">()</span>
<span class="n">ancestors</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s">"Node"</span><span class="p">,</span> <span class="n">viewonly</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">secondary</span><span class="o">=</span><span class="n">secondary</span><span class="p">,</span>
<span class="n">primaryjoin</span><span class="o">=</span><span class="nb">id</span> <span class="o">==</span> <span class="n">secondary</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">id</span><span class="p">,</span>
<span class="n">secondaryjoin</span><span class="o">=</span><span class="n">secondary</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">ancestor_id</span> <span class="o">==</span> <span class="nb">id</span><span class="p">,</span>
<span class="n">order_by</span><span class="o">=</span><span class="n">path</span><span class="p">)</span>
<span class="nd">@property</span>
<span class="k">def</span> <span class="nf">depth</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">path</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s">"."</span><span class="p">))</span> <span class="o">-</span> <span class="mi">1</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="s">"Node(id={})"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">id</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="n">root_depth</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">depth</span>
<span class="n">s</span> <span class="o">=</span> <span class="p">[</span><span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">id</span><span class="p">)]</span>
<span class="n">s</span><span class="o">.</span><span class="n">extend</span><span class="p">(((</span><span class="n">n</span><span class="o">.</span><span class="n">depth</span> <span class="o">-</span> <span class="n">root_depth</span><span class="p">)</span> <span class="o">*</span> <span class="s">" "</span> <span class="o">+</span> <span class="nb">str</span><span class="p">(</span><span class="n">n</span><span class="o">.</span><span class="n">id</span><span class="p">))</span>
<span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">descendants</span><span class="p">)</span>
<span class="k">return</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">s</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">move_to</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">new_parent</span><span class="p">):</span>
<span class="n">new_path</span> <span class="o">=</span> <span class="n">new_parent</span><span class="o">.</span><span class="n">path</span> <span class="o">+</span> <span class="s">"."</span> <span class="o">+</span> <span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">id</span><span class="p">)</span>
<span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">descendants</span><span class="p">:</span>
<span class="n">n</span><span class="o">.</span><span class="n">path</span> <span class="o">=</span> <span class="n">new_path</span> <span class="o">+</span> <span class="n">n</span><span class="o">.</span><span class="n">path</span><span class="p">[</span><span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">path</span><span class="p">):]</span>
<span class="bp">self</span><span class="o">.</span><span class="n">path</span> <span class="o">=</span> <span class="n">new_path</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__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="s">"postgresql://scott:tiger@localhost/test"</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">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">engine</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s">"-"</span> <span class="o">*</span> <span class="mi">80</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s">"create a tree"</span><span class="p">)</span>
<span class="n">session</span><span class="o">.</span><span class="n">add_all</span><span class="p">([</span>
<span class="n">Node</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">path</span><span class="o">=</span><span class="s">"1"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.2"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.3"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.3.4"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.3.5"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">6</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.3.6"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">7</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.7"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">8</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.7.8"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">9</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.7.9"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">10</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.7.9.10"</span><span class="p">),</span>
<span class="n">Node</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">11</span><span class="p">,</span> <span class="n">path</span><span class="o">=</span><span class="s">"1.7.11"</span><span class="p">),</span>
<span class="p">])</span>
<span class="n">session</span><span class="o">.</span><span class="n">flush</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">1</span><span class="p">)))</span>
<span class="k">print</span><span class="p">(</span><span class="s">"-"</span> <span class="o">*</span> <span class="mi">80</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s">"move 7 under 3"</span><span class="p">)</span>
<span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">7</span><span class="p">)</span><span class="o">.</span><span class="n">move_to</span><span class="p">(</span><span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">3</span><span class="p">))</span>
<span class="n">session</span><span class="o">.</span><span class="n">flush</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">1</span><span class="p">)))</span>
<span class="k">print</span><span class="p">(</span><span class="s">"-"</span> <span class="o">*</span> <span class="mi">80</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s">"move 3 under 2"</span><span class="p">)</span>
<span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="o">.</span><span class="n">move_to</span><span class="p">(</span><span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
<span class="n">session</span><span class="o">.</span><span class="n">flush</span><span class="p">()</span>
<span class="k">print</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">1</span><span class="p">)))</span>
<span class="k">print</span><span class="p">(</span><span class="s">"-"</span> <span class="o">*</span> <span class="mi">80</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s">"find the ancestors of 10"</span><span class="p">)</span>
<span class="k">print</span><span class="p">([</span><span class="n">n</span><span class="o">.</span><span class="n">id</span> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Node</span><span class="p">)</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span><span class="o">.</span><span class="n">ancestors</span><span class="p">])</span>
<span class="n">session</span><span class="o">.</span><span class="n">close</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">drop_all</span><span class="p">(</span><span class="n">engine</span><span class="p">)</span></pre></div>
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