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examples.join_conditions.threeway
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SQLAlchemy 0.9 Documentation
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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.join_conditions.threeway</h1><div class="highlight"><pre>
<span class="sd">"""Illustrate a "three way join" - where a primary table joins to a remote</span>
<span class="sd">table via an association table, but then the primary table also needs</span>
<span class="sd">to refer to some columns in the remote table directly.</span>
<span class="sd">E.g.::</span>
<span class="sd"> first.first_id -> second.first_id</span>
<span class="sd"> second.other_id --> partitioned.other_id</span>
<span class="sd"> first.partition_key ---------------------> partitioned.partition_key</span>
<span class="sd">For a relationship like this, "second" is a lot like a "secondary" table,</span>
<span class="sd">but the mechanics aren't present within the "secondary" feature to allow</span>
<span class="sd">for the join directly between first and partitioned. Instead, we</span>
<span class="sd">will derive a selectable from partitioned and second combined together, then</span>
<span class="sd">link first to that derived selectable.</span>
<span class="sd">If we define the derived selectable as::</span>
<span class="sd"> second JOIN partitioned ON second.other_id = partitioned.other_id</span>
<span class="sd">A JOIN from first to this derived selectable is then::</span>
<span class="sd"> first JOIN (second JOIN partitioned</span>
<span class="sd"> ON second.other_id = partitioned.other_id)</span>
<span class="sd"> ON first.first_id = second.first_id AND</span>
<span class="sd"> first.partition_key = partitioned.partition_key</span>
<span class="sd">We will use the "non primary mapper" feature in order to produce this.</span>
<span class="sd">A non primary mapper is essentially an "extra" :func:`.mapper` that we can</span>
<span class="sd">use to associate a particular class with some selectable that is</span>
<span class="sd">not its usual mapped table. It is used only when called upon within</span>
<span class="sd">a Query (or a :func:`.relationship`).</span>
<span class="sd">"""</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</span> <span class="kn">import</span> <span class="o">*</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="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">First</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">'first'</span>
<span class="n">first_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">partition_key</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">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="p">(</span><span class="s">"First(</span><span class="si">%s</span><span class="s">, </span><span class="si">%s</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">first_id</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">partition_key</span><span class="p">))</span>
<span class="k">class</span> <span class="nc">Second</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">'second'</span>
<span class="n">first_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">other_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="k">class</span> <span class="nc">Partitioned</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">'partitioned'</span>
<span class="n">other_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">partition_key</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="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="p">(</span><span class="s">"Partitioned(</span><span class="si">%s</span><span class="s">, </span><span class="si">%s</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">other_id</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">partition_key</span><span class="p">))</span>
<span class="n">j</span> <span class="o">=</span> <span class="n">join</span><span class="p">(</span><span class="n">Partitioned</span><span class="p">,</span> <span class="n">Second</span><span class="p">,</span> <span class="n">Partitioned</span><span class="o">.</span><span class="n">other_id</span> <span class="o">==</span> <span class="n">Second</span><span class="o">.</span><span class="n">other_id</span><span class="p">)</span>
<span class="n">partitioned_second</span> <span class="o">=</span> <span class="n">mapper</span><span class="p">(</span><span class="n">Partitioned</span><span class="p">,</span> <span class="n">j</span><span class="p">,</span> <span class="n">non_primary</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">properties</span><span class="o">=</span><span class="p">{</span>
<span class="c"># note we need to disambiguate columns here - the join()</span>
<span class="c"># will provide them as j.c.<tablename>_<colname> for access,</span>
<span class="c"># but they retain their real names in the mapping</span>
<span class="s">"other_id"</span><span class="p">:</span> <span class="p">[</span><span class="n">j</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">partitioned_other_id</span><span class="p">,</span> <span class="n">j</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">second_other_id</span><span class="p">],</span>
<span class="p">})</span>
<span class="n">First</span><span class="o">.</span><span class="n">partitioned</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span>
<span class="n">partitioned_second</span><span class="p">,</span>
<span class="n">primaryjoin</span><span class="o">=</span><span class="n">and_</span><span class="p">(</span>
<span class="n">First</span><span class="o">.</span><span class="n">partition_key</span> <span class="o">==</span> <span class="n">partitioned_second</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">partition_key</span><span class="p">,</span>
<span class="n">First</span><span class="o">.</span><span class="n">first_id</span> <span class="o">==</span> <span class="n">foreign</span><span class="p">(</span><span class="n">partitioned_second</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">first_id</span><span class="p">)</span>
<span class="p">),</span> <span class="n">innerjoin</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="c"># when using any database other than SQLite, we will get a nested</span>
<span class="c"># join, e.g. "first JOIN (partitioned JOIN second ON ..) ON ..".</span>
<span class="c"># On SQLite, SQLAlchemy needs to render a full subquery.</span>
<span class="n">e</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">e</span><span class="p">)</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">Session</span><span class="p">(</span><span class="n">e</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">add_all</span><span class="p">([</span>
<span class="n">First</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">partition_key</span><span class="o">=</span><span class="s">'p1'</span><span class="p">),</span>
<span class="n">First</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">partition_key</span><span class="o">=</span><span class="s">'p1'</span><span class="p">),</span>
<span class="n">First</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">partition_key</span><span class="o">=</span><span class="s">'p2'</span><span class="p">),</span>
<span class="n">Second</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">1</span><span class="p">),</span>
<span class="n">Second</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">1</span><span class="p">),</span>
<span class="n">Second</span><span class="p">(</span><span class="n">first_id</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">2</span><span class="p">),</span>
<span class="n">Partitioned</span><span class="p">(</span><span class="n">partition_key</span><span class="o">=</span><span class="s">'p1'</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">1</span><span class="p">),</span>
<span class="n">Partitioned</span><span class="p">(</span><span class="n">partition_key</span><span class="o">=</span><span class="s">'p1'</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">2</span><span class="p">),</span>
<span class="n">Partitioned</span><span class="p">(</span><span class="n">partition_key</span><span class="o">=</span><span class="s">'p2'</span><span class="p">,</span> <span class="n">other_id</span><span class="o">=</span><span class="mi">2</span><span class="p">),</span>
<span class="p">])</span>
<span class="n">s</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">First</span><span class="p">,</span> <span class="n">Partitioned</span><span class="p">)</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">First</span><span class="o">.</span><span class="n">partitioned</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="n">row</span><span class="p">)</span>
<span class="k">for</span> <span class="n">f</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">First</span><span class="p">):</span>
<span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">f</span><span class="o">.</span><span class="n">partitioned</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="n">f</span><span class="o">.</span><span class="n">partition_key</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">partition_key</span><span class="p">)</span></pre></div>
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