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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.nested_sets.nested_sets</h1><div class="highlight"><pre>
<span class="sd">"""Celko's "Nested Sets" Tree Structure.</span>
<span class="sd">http://www.intelligententerprise.com/001020/celko.jhtml</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="kn">import</span> <span class="p">(</span><span class="n">create_engine</span><span class="p">,</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">select</span><span class="p">,</span> <span class="n">case</span><span class="p">,</span>
<span class="n">func</span><span class="p">)</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="n">Session</span><span class="p">,</span> <span class="n">aliased</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</span> <span class="kn">import</span> <span class="n">event</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">Employee</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">'personnel'</span>
<span class="n">__mapper_args__</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'batch'</span><span class="p">:</span> <span class="bp">False</span> <span class="c"># allows extension to fire for each</span>
<span class="c"># instance before going to the next.</span>
<span class="p">}</span>
<span class="n">parent</span> <span class="o">=</span> <span class="bp">None</span>
<span class="n">emp</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">primary_key</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">left</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="s">"lft"</span><span class="p">,</span> <span class="n">Integer</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">right</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="s">"rgt"</span><span class="p">,</span> <span class="n">Integer</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="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">"Employee(</span><span class="si">%s</span><span class="s">, </span><span class="si">%d</span><span class="s">, </span><span class="si">%d</span><span class="s">)"</span> <span class="o">%</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">emp</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">left</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">right</span><span class="p">)</span>
<span class="nd">@event.listens_for</span><span class="p">(</span><span class="n">Employee</span><span class="p">,</span> <span class="s">"before_insert"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">before_insert</span><span class="p">(</span><span class="n">mapper</span><span class="p">,</span> <span class="n">connection</span><span class="p">,</span> <span class="n">instance</span><span class="p">):</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">instance</span><span class="o">.</span><span class="n">parent</span><span class="p">:</span>
<span class="n">instance</span><span class="o">.</span><span class="n">left</span> <span class="o">=</span> <span class="mi">1</span>
<span class="n">instance</span><span class="o">.</span><span class="n">right</span> <span class="o">=</span> <span class="mi">2</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">personnel</span> <span class="o">=</span> <span class="n">mapper</span><span class="o">.</span><span class="n">mapped_table</span>
<span class="n">right_most_sibling</span> <span class="o">=</span> <span class="n">connection</span><span class="o">.</span><span class="n">scalar</span><span class="p">(</span>
<span class="n">select</span><span class="p">([</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">rgt</span><span class="p">])</span><span class="o">.</span>
<span class="n">where</span><span class="p">(</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">emp</span> <span class="o">==</span> <span class="n">instance</span><span class="o">.</span><span class="n">parent</span><span class="o">.</span><span class="n">emp</span><span class="p">)</span>
<span class="p">)</span>
<span class="n">connection</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span>
<span class="n">personnel</span><span class="o">.</span><span class="n">update</span><span class="p">(</span>
<span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">rgt</span> <span class="o">>=</span> <span class="n">right_most_sibling</span><span class="p">)</span><span class="o">.</span><span class="n">values</span><span class="p">(</span>
<span class="n">lft</span><span class="o">=</span><span class="n">case</span><span class="p">(</span>
<span class="p">[(</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">lft</span> <span class="o">></span> <span class="n">right_most_sibling</span><span class="p">,</span>
<span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">lft</span> <span class="o">+</span> <span class="mi">2</span><span class="p">)],</span>
<span class="n">else_</span><span class="o">=</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">lft</span>
<span class="p">),</span>
<span class="n">rgt</span><span class="o">=</span><span class="n">case</span><span class="p">(</span>
<span class="p">[(</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">rgt</span> <span class="o">>=</span> <span class="n">right_most_sibling</span><span class="p">,</span>
<span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">rgt</span> <span class="o">+</span> <span class="mi">2</span><span class="p">)],</span>
<span class="n">else_</span><span class="o">=</span><span class="n">personnel</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">rgt</span>
<span class="p">)</span>
<span class="p">)</span>
<span class="p">)</span>
<span class="n">instance</span><span class="o">.</span><span class="n">left</span> <span class="o">=</span> <span class="n">right_most_sibling</span>
<span class="n">instance</span><span class="o">.</span><span class="n">right</span> <span class="o">=</span> <span class="n">right_most_sibling</span> <span class="o">+</span> <span class="mi">1</span>
<span class="c"># before_update() would be needed to support moving of nodes</span>
<span class="c"># after_delete() would be needed to support removal of nodes.</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">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">bind</span><span class="o">=</span><span class="n">engine</span><span class="p">)</span>
<span class="n">albert</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Albert'</span><span class="p">)</span>
<span class="n">bert</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Bert'</span><span class="p">)</span>
<span class="n">chuck</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Chuck'</span><span class="p">)</span>
<span class="n">donna</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Donna'</span><span class="p">)</span>
<span class="n">eddie</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Eddie'</span><span class="p">)</span>
<span class="n">fred</span> <span class="o">=</span> <span class="n">Employee</span><span class="p">(</span><span class="n">emp</span><span class="o">=</span><span class="s">'Fred'</span><span class="p">)</span>
<span class="n">bert</span><span class="o">.</span><span class="n">parent</span> <span class="o">=</span> <span class="n">albert</span>
<span class="n">chuck</span><span class="o">.</span><span class="n">parent</span> <span class="o">=</span> <span class="n">albert</span>
<span class="n">donna</span><span class="o">.</span><span class="n">parent</span> <span class="o">=</span> <span class="n">chuck</span>
<span class="n">eddie</span><span class="o">.</span><span class="n">parent</span> <span class="o">=</span> <span class="n">chuck</span>
<span class="n">fred</span><span class="o">.</span><span class="n">parent</span> <span class="o">=</span> <span class="n">chuck</span>
<span class="c"># the order of "add" is important here. elements must be added in</span>
<span class="c"># the order in which they should be INSERTed.</span>
<span class="n">session</span><span class="o">.</span><span class="n">add_all</span><span class="p">([</span><span class="n">albert</span><span class="p">,</span> <span class="n">bert</span><span class="p">,</span> <span class="n">chuck</span><span class="p">,</span> <span class="n">donna</span><span class="p">,</span> <span class="n">eddie</span><span class="p">,</span> <span class="n">fred</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="k">print</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">Employee</span><span class="p">)</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="c"># 1. Find an employee and all their supervisors, no matter how deep the tree.</span>
<span class="n">ealias</span> <span class="o">=</span> <span class="n">aliased</span><span class="p">(</span><span class="n">Employee</span><span class="p">)</span>
<span class="k">print</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">Employee</span><span class="p">)</span><span class="o">.</span>\
<span class="nb">filter</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">left</span><span class="o">.</span><span class="n">between</span><span class="p">(</span><span class="n">Employee</span><span class="o">.</span><span class="n">left</span><span class="p">,</span> <span class="n">Employee</span><span class="o">.</span><span class="n">right</span><span class="p">))</span><span class="o">.</span>\
<span class="nb">filter</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">emp</span> <span class="o">==</span> <span class="s">'Eddie'</span><span class="p">)</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="c">#2. Find the employee and all their subordinates.</span>
<span class="c"># (This query has a nice symmetry with the first query.)</span>
<span class="k">print</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">Employee</span><span class="p">)</span><span class="o">.</span>\
<span class="nb">filter</span><span class="p">(</span><span class="n">Employee</span><span class="o">.</span><span class="n">left</span><span class="o">.</span><span class="n">between</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">left</span><span class="p">,</span> <span class="n">ealias</span><span class="o">.</span><span class="n">right</span><span class="p">))</span><span class="o">.</span>\
<span class="nb">filter</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">emp</span> <span class="o">==</span> <span class="s">'Chuck'</span><span class="p">)</span><span class="o">.</span><span class="n">all</span><span class="p">())</span>
<span class="c">#3. Find the level of each node, so you can print the tree</span>
<span class="c"># as an indented listing.</span>
<span class="k">for</span> <span class="n">indentation</span><span class="p">,</span> <span class="n">employee</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">func</span><span class="o">.</span><span class="n">count</span><span class="p">(</span><span class="n">Employee</span><span class="o">.</span><span class="n">emp</span><span class="p">)</span><span class="o">.</span><span class="n">label</span><span class="p">(</span><span class="s">'indentation'</span><span class="p">)</span> <span class="o">-</span> <span class="mi">1</span><span class="p">,</span> <span class="n">ealias</span><span class="p">)</span><span class="o">.</span>\
<span class="nb">filter</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">left</span><span class="o">.</span><span class="n">between</span><span class="p">(</span><span class="n">Employee</span><span class="o">.</span><span class="n">left</span><span class="p">,</span> <span class="n">Employee</span><span class="o">.</span><span class="n">right</span><span class="p">))</span><span class="o">.</span>\
<span class="n">group_by</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">emp</span><span class="p">)</span><span class="o">.</span>\
<span class="n">order_by</span><span class="p">(</span><span class="n">ealias</span><span class="o">.</span><span class="n">left</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="s">" "</span> <span class="o">*</span> <span class="n">indentation</span> <span class="o">+</span> <span class="nb">str</span><span class="p">(</span><span class="n">employee</span><span class="p">))</span></pre></div>
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