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SQLAlchemy 1.2 Documentation
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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.elementtree.pickle</h1><div class="highlight"><pre>
<span></span><span class="sd">"""</span>
<span class="sd">illustrates a quick and dirty way to persist an XML document expressed using</span>
<span class="sd">ElementTree and pickle.</span>
<span class="sd">This is a trivial example using PickleType to marshal/unmarshal the ElementTree</span>
<span class="sd">document into a binary column. Compare to explicit.py which stores the</span>
<span class="sd">individual components of the ElementTree structure in distinct rows using two</span>
<span class="sd">additional mapped entities. Note that the usage of both styles of persistence</span>
<span class="sd">are identical, as is the structure of the main Document class.</span>
<span class="sd">"""</span>
<span class="kn">import</span> <span class="nn">os</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="kn">from</span> <span class="nn">xml.etree</span> <span class="k">import</span> <span class="n">ElementTree</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">Integer</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">MetaData</span>
<span class="kn">from</span> <span class="nn">sqlalchemy</span> <span class="k">import</span> <span class="n">PickleType</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</span> <span class="k">import</span> <span class="n">Table</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">mapper</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="k">import</span> <span class="n">Session</span>
<span class="n">e</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">meta</span> <span class="o">=</span> <span class="n">MetaData</span><span class="p">()</span>
<span class="c1"># setup a comparator for the PickleType since it's a mutable</span>
<span class="c1"># element.</span>
<span class="k">def</span> <span class="nf">are_elements_equal</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">==</span> <span class="n">y</span>
<span class="c1"># stores a top level record of an XML document.</span>
<span class="c1"># the "element" column will store the ElementTree document as a BLOB.</span>
<span class="n">documents</span> <span class="o">=</span> <span class="n">Table</span><span class="p">(</span>
<span class="s2">"documents"</span><span class="p">,</span>
<span class="n">meta</span><span class="p">,</span>
<span class="n">Column</span><span class="p">(</span><span class="s2">"document_id"</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">Column</span><span class="p">(</span><span class="s2">"filename"</span><span class="p">,</span> <span class="n">String</span><span class="p">(</span><span class="mi">30</span><span class="p">),</span> <span class="n">unique</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
<span class="n">Column</span><span class="p">(</span><span class="s2">"element"</span><span class="p">,</span> <span class="n">PickleType</span><span class="p">(</span><span class="n">comparator</span><span class="o">=</span><span class="n">are_elements_equal</span><span class="p">)),</span>
<span class="p">)</span>
<span class="n">meta</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="c1"># our document class. contains a string name,</span>
<span class="c1"># and the ElementTree root element.</span>
<span class="k">class</span> <span class="nc">Document</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">element</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">filename</span> <span class="o">=</span> <span class="n">name</span>
<span class="bp">self</span><span class="o">.</span><span class="n">element</span> <span class="o">=</span> <span class="n">element</span>
<span class="c1"># setup mapper.</span>
<span class="n">mapper</span><span class="p">(</span><span class="n">Document</span><span class="p">,</span> <span class="n">documents</span><span class="p">)</span>
<span class="c1"># time to test !</span>
<span class="c1"># get ElementTree document</span>
<span class="n">filename</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">dirname</span><span class="p">(</span><span class="vm">__file__</span><span class="p">),</span> <span class="s2">"test.xml"</span><span class="p">)</span>
<span class="n">doc</span> <span class="o">=</span> <span class="n">ElementTree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span>
<span class="c1"># save to DB</span>
<span class="n">session</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">session</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">Document</span><span class="p">(</span><span class="s2">"test.xml"</span><span class="p">,</span> <span class="n">doc</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="c1"># restore</span>
<span class="n">document</span> <span class="o">=</span> <span class="n">session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">Document</span><span class="p">)</span><span class="o">.</span><span class="n">filter_by</span><span class="p">(</span><span class="n">filename</span><span class="o">=</span><span class="s2">"test.xml"</span><span class="p">)</span><span class="o">.</span><span class="n">first</span><span class="p">()</span>
<span class="c1"># print</span>
<span class="n">document</span><span class="o">.</span><span class="n">element</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span></pre></div>
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