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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.dogpile_caching.advanced</h1><div class="highlight"><pre>
<span></span><span class="sd">"""Illustrate usage of Query combined with the FromCache option,</span>
<span class="sd">including front-end loading, cache invalidation and collection caching.</span>
<span class="sd">"""</span>
<span class="kn">from</span> <span class="nn">.caching_query</span> <span class="k">import</span> <span class="n">FromCache</span>
<span class="kn">from</span> <span class="nn">.caching_query</span> <span class="k">import</span> <span class="n">RelationshipCache</span>
<span class="kn">from</span> <span class="nn">.environment</span> <span class="k">import</span> <span class="n">Session</span>
<span class="kn">from</span> <span class="nn">.model</span> <span class="k">import</span> <span class="n">cache_address_bits</span>
<span class="kn">from</span> <span class="nn">.model</span> <span class="k">import</span> <span class="n">Person</span>
<span class="k">def</span> <span class="nf">load_name_range</span><span class="p">(</span><span class="n">start</span><span class="p">,</span> <span class="n">end</span><span class="p">,</span> <span class="n">invalidate</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span>
<span class="sd">"""Load Person objects on a range of names.</span>
<span class="sd"> start/end are integers, range is then</span>
<span class="sd"> "person <start>" - "person <end>".</span>
<span class="sd"> The cache option we set up is called "name_range", indicating</span>
<span class="sd"> a range of names for the Person class.</span>
<span class="sd"> The `Person.addresses` collections are also cached. Its basically</span>
<span class="sd"> another level of tuning here, as that particular cache option</span>
<span class="sd"> can be transparently replaced with joinedload(Person.addresses).</span>
<span class="sd"> The effect is that each Person and their Address collection</span>
<span class="sd"> is cached either together or separately, affecting the kind of</span>
<span class="sd"> SQL that emits for unloaded Person objects as well as the distribution</span>
<span class="sd"> of data within the cache.</span>
<span class="sd"> """</span>
<span class="n">q</span> <span class="o">=</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">Person</span><span class="p">)</span>
<span class="o">.</span><span class="n">filter</span><span class="p">(</span>
<span class="n">Person</span><span class="o">.</span><span class="n">name</span><span class="o">.</span><span class="n">between</span><span class="p">(</span><span class="s2">"person </span><span class="si">%.2d</span><span class="s2">"</span> <span class="o">%</span> <span class="n">start</span><span class="p">,</span> <span class="s2">"person </span><span class="si">%.2d</span><span class="s2">"</span> <span class="o">%</span> <span class="n">end</span><span class="p">)</span>
<span class="p">)</span>
<span class="o">.</span><span class="n">options</span><span class="p">(</span><span class="n">cache_address_bits</span><span class="p">)</span>
<span class="o">.</span><span class="n">options</span><span class="p">(</span><span class="n">FromCache</span><span class="p">(</span><span class="s2">"default"</span><span class="p">,</span> <span class="s2">"name_range"</span><span class="p">))</span>
<span class="p">)</span>
<span class="c1"># have the "addresses" collection cached separately</span>
<span class="c1"># each lazyload of Person.addresses loads from cache.</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">q</span><span class="o">.</span><span class="n">options</span><span class="p">(</span><span class="n">RelationshipCache</span><span class="p">(</span><span class="n">Person</span><span class="o">.</span><span class="n">addresses</span><span class="p">,</span> <span class="s2">"default"</span><span class="p">))</span>
<span class="c1"># alternatively, eagerly load the "addresses" collection, so that they'd</span>
<span class="c1"># be cached together. This issues a bigger SQL statement and caches</span>
<span class="c1"># a single, larger value in the cache per person rather than two</span>
<span class="c1"># separate ones.</span>
<span class="c1"># q = q.options(joinedload(Person.addresses))</span>
<span class="c1"># if requested, invalidate the cache on current criterion.</span>
<span class="k">if</span> <span class="n">invalidate</span><span class="p">:</span>
<span class="n">q</span><span class="o">.</span><span class="n">invalidate</span><span class="p">()</span>
<span class="k">return</span> <span class="n">q</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"two through twelve, possibly from cache:</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">", "</span><span class="o">.</span><span class="n">join</span><span class="p">([</span><span class="n">p</span><span class="o">.</span><span class="n">name</span> <span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">12</span><span class="p">)]))</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">twenty five through forty, possibly from cache:</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">", "</span><span class="o">.</span><span class="n">join</span><span class="p">([</span><span class="n">p</span><span class="o">.</span><span class="n">name</span> <span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">25</span><span class="p">,</span> <span class="mi">40</span><span class="p">)]))</span>
<span class="c1"># loading them again, no SQL is emitted</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">two through twelve, from the cache:</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">", "</span><span class="o">.</span><span class="n">join</span><span class="p">([</span><span class="n">p</span><span class="o">.</span><span class="n">name</span> <span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">12</span><span class="p">)]))</span>
<span class="c1"># but with invalidate, they are</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">twenty five through forty, invalidate first:</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">", "</span><span class="o">.</span><span class="n">join</span><span class="p">([</span><span class="n">p</span><span class="o">.</span><span class="n">name</span> <span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">25</span><span class="p">,</span> <span class="mi">40</span><span class="p">,</span> <span class="kc">True</span><span class="p">)]))</span>
<span class="c1"># illustrate the address loading from either cache/already</span>
<span class="c1"># on the Person</span>
<span class="nb">print</span><span class="p">(</span>
<span class="s2">"</span><span class="se">\n\n</span><span class="s2">People plus addresses, two through twelve, addresses "</span>
<span class="s2">"possibly from cache"</span>
<span class="p">)</span>
<span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">12</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">format_full</span><span class="p">())</span>
<span class="c1"># illustrate the address loading from either cache/already</span>
<span class="c1"># on the Person</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"</span><span class="se">\n\n</span><span class="s2">People plus addresses, two through twelve, addresses from cache"</span><span class="p">)</span>
<span class="k">for</span> <span class="n">p</span> <span class="ow">in</span> <span class="n">load_name_range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">12</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">format_full</span><span class="p">())</span>
<span class="nb">print</span><span class="p">(</span>
<span class="s2">"</span><span class="se">\n\n</span><span class="s2">If this was the first run of advanced.py, try "</span>
<span class="s2">"a second run. Only one SQL statement will be emitted."</span>
<span class="p">)</span></pre></div>
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