Redis caching with cache-aside pattern and TTL management

<p>I have expensive database queries for search results I want to cache in Redis. I need a clean cache-aside pattern that serializes Pydantic models, handles Redis unavailability gracefully, and avoids stale data.</p>

<p>Cache-aside pattern with Pydantic serialization:</p> <div class="highlight"><pre><span></span><code><span class="kn">import</span><span class="w"> </span><span class="nn">json</span> <span class="kn">from</span><span class="w"> </span><span class="nn">typing</span><span class="w"> </span><span class="kn">import</span> <span class="n">Optional</span><span class="p">,</span> <span class="n">TypeVar</span><span class="p">,</span> <span class="n">Type</span> <span class="kn">from</span><span class="w"> </span><span class="nn">pydantic</span><span class="w"> </span><span class="kn">import</span> <span class="n">BaseModel</span> <span class="kn">import</span><span class="w"> </span><span class="nn">redis.asyncio</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">redis</span> <span class="n">T</span> <span class="o">=</span> <span class="n">TypeVar</span><span class="p">(</span><span class="s1">'T'</span><span class="p">,</span> <span class="n">bound</span><span class="o">=</span><span class="n">BaseModel</span><span class="p">)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">cache_get</span><span class="p">(</span><span class="n">redis_client</span><span class="p">:</span> <span class="n">redis</span><span class="o">.</span><span class="n">Redis</span><span class="p">,</span> <span class="n">key</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">model</span><span class="p">:</span> <span class="n">Type</span><span class="p">[</span><span class="n">T</span><span class="p">])</span> <span class="o">-&gt;</span> <span class="n">Optional</span><span class="p">[</span><span class="n">T</span><span class="p">]:</span> <span class="w"> </span><span class="sd">"""Cache read -- returns None on miss or Redis error."""</span> <span class="k">try</span><span class="p">:</span> <span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">redis_client</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">key</span><span class="p">)</span> <span class="k">if</span> <span class="n">data</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span> <span class="k">return</span> <span class="kc">None</span> <span class="k">return</span> <span class="n">model</span><span class="o">.</span><span class="n">model_validate_json</span><span class="p">(</span><span class="n">data</span><span class="p">)</span> <span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="k">return</span> <span class="kc">None</span> <span class="c1"># Fail open on Redis errors</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">cache_set</span><span class="p">(</span> <span class="n">redis_client</span><span class="p">:</span> <span class="n">redis</span><span class="o">.</span><span class="n">Redis</span><span class="p">,</span> <span class="n">key</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">value</span><span class="p">:</span> <span class="n">BaseModel</span><span class="p">,</span> <span class="n">ttl</span><span class="p">:</span> <span class="nb">int</span> <span class="o">=</span> <span class="mi">300</span> <span class="p">)</span> <span class="o">-&gt;</span> <span class="kc">None</span><span class="p">:</span> <span class="w"> </span><span class="sd">"""Cache write -- silently fails if Redis unavailable."""</span> <span class="k">try</span><span class="p">:</span> <span class="k">await</span> <span class="n">redis_client</span><span class="o">.</span><span class="n">setex</span><span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="n">ttl</span><span class="p">,</span> <span class="n">value</span><span class="o">.</span><span class="n">model_dump_json</span><span class="p">())</span> <span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="k">pass</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">cache_invalidate</span><span class="p">(</span><span class="n">redis_client</span><span class="p">:</span> <span class="n">redis</span><span class="o">.</span><span class="n">Redis</span><span class="p">,</span> <span class="n">pattern</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kc">None</span><span class="p">:</span> <span class="w"> </span><span class="sd">"""Delete all keys matching pattern."""</span> <span class="k">try</span><span class="p">:</span> <span class="n">keys</span> <span class="o">=</span> <span class="k">await</span> <span class="n">redis_client</span><span class="o">.</span><span class="n">keys</span><span class="p">(</span><span class="n">pattern</span><span class="p">)</span> <span class="k">if</span> <span class="n">keys</span><span class="p">:</span> <span class="k">await</span> <span class="n">redis_client</span><span class="o">.</span><span class="n">delete</span><span class="p">(</span><span class="o">*</span><span class="n">keys</span><span class="p">)</span> <span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="k">pass</span> <span class="c1"># Usage:</span> <span class="nd">@router</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'/search'</span><span class="p">)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">search</span><span class="p">(</span><span class="n">q</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">db</span><span class="p">:</span> <span class="n">DbSession</span><span class="p">,</span> <span class="n">redis</span><span class="o">=</span><span class="n">Depends</span><span class="p">(</span><span class="n">get_redis</span><span class="p">)):</span> <span class="n">cache_key</span> <span class="o">=</span> <span class="sa">f</span><span class="s1">'search:</span><span class="si">{</span><span class="nb">hash</span><span class="p">(</span><span class="n">q</span><span class="o">.</span><span class="n">lower</span><span class="p">()</span><span class="o">.</span><span class="n">strip</span><span class="p">())</span><span class="si">}</span><span class="s1">'</span> <span class="n">cached</span> <span class="o">=</span> <span class="k">await</span> <span class="n">cache_get</span><span class="p">(</span><span class="n">redis</span><span class="p">,</span> <span class="n">cache_key</span><span class="p">,</span> <span class="n">SearchResponse</span><span class="p">)</span> <span class="k">if</span> <span class="n">cached</span><span class="p">:</span> <span class="k">return</span> <span class="n">cached</span> <span class="n">results</span> <span class="o">=</span> <span class="k">await</span> <span class="n">do_search</span><span class="p">(</span><span class="n">db</span><span class="p">,</span> <span class="n">q</span><span class="p">)</span> <span class="n">response</span> <span class="o">=</span> <span class="n">SearchResponse</span><span class="p">(</span><span class="n">results</span><span class="o">=</span><span class="n">results</span><span class="p">)</span> <span class="k">await</span> <span class="n">cache_set</span><span class="p">(</span><span class="n">redis</span><span class="p">,</span> <span class="n">cache_key</span><span class="p">,</span> <span class="n">response</span><span class="p">,</span> <span class="n">ttl</span><span class="o">=</span><span class="mi">300</span><span class="p">)</span> <span class="k">return</span> <span class="n">response</span> </code></pre></div> <p>Key points: - Always fail open on Redis errors -- cache is an optimization, not a requirement - model_validate_json/model_dump_json for efficient Pydantic serialization - Invalidate by pattern when underlying data changes - Include all query parameters in cache key for correct scoping - setex (SET + EXPIRY) is atomic -- prevents keys without TTL</p>