Pydantic v2 model for API request and response with field aliasing

<p>My API uses snake_case internally (Python convention) but the frontend expects camelCase JSON. I need Pydantic models that accept and output camelCase JSON while keeping snake_case attribute names in Python code.</p>

<p>Use <code>model_config</code> with <code>alias_generator</code> for automatic camelCase conversion:</p> <div class="highlight"><pre><span></span><code><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="p">,</span> <span class="n">ConfigDict</span><span class="p">,</span> <span class="n">Field</span> <span class="kn">from</span><span class="w"> </span><span class="nn">pydantic.alias_generators</span><span class="w"> </span><span class="kn">import</span> <span class="n">to_camel</span> <span class="kn">import</span><span class="w"> </span><span class="nn">uuid</span> <span class="kn">from</span><span class="w"> </span><span class="nn">datetime</span><span class="w"> </span><span class="kn">import</span> <span class="n">datetime</span> <span class="k">class</span><span class="w"> </span><span class="nc">APIModel</span><span class="p">(</span><span class="n">BaseModel</span><span class="p">):</span> <span class="w"> </span><span class="sd">"""Base model for all API request/response schemas."""</span> <span class="n">model_config</span> <span class="o">=</span> <span class="n">ConfigDict</span><span class="p">(</span> <span class="n">alias_generator</span><span class="o">=</span><span class="n">to_camel</span><span class="p">,</span> <span class="n">populate_by_name</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="c1"># Allow snake_case in Python code</span> <span class="p">)</span> <span class="k">class</span><span class="w"> </span><span class="nc">TraceResponse</span><span class="p">(</span><span class="n">APIModel</span><span class="p">):</span> <span class="nb">id</span><span class="p">:</span> <span class="n">uuid</span><span class="o">.</span><span class="n">UUID</span> <span class="n">title</span><span class="p">:</span> <span class="nb">str</span> <span class="n">context_text</span><span class="p">:</span> <span class="nb">str</span> <span class="c1"># -&gt; contextText in JSON</span> <span class="n">solution_text</span><span class="p">:</span> <span class="nb">str</span> <span class="c1"># -&gt; solutionText in JSON</span> <span class="n">trust_score</span><span class="p">:</span> <span class="nb">float</span> <span class="c1"># -&gt; trustScore in JSON</span> <span class="n">created_at</span><span class="p">:</span> <span class="n">datetime</span> <span class="c1"># Serialize with aliases:</span> <span class="n">trace_response</span><span class="o">.</span><span class="n">model_dump</span><span class="p">(</span><span class="n">by_alias</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="c1"># -&gt; {'id': ..., 'contextText': ..., 'solutionText': ...}</span> <span class="c1"># FastAPI: tell it to use aliases in responses:</span> <span class="nd">@router</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'/traces/</span><span class="si">{trace_id}</span><span class="s1">'</span><span class="p">,</span> <span class="n">response_model</span><span class="o">=</span><span class="n">TraceResponse</span><span class="p">)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">get_trace</span><span class="p">(</span><span class="n">trace_id</span><span class="p">:</span> <span class="n">uuid</span><span class="o">.</span><span class="n">UUID</span><span class="p">):</span> <span class="n">trace</span> <span class="o">=</span> <span class="k">await</span> <span class="n">fetch_trace</span><span class="p">(</span><span class="n">trace_id</span><span class="p">)</span> <span class="k">return</span> <span class="n">JSONResponse</span><span class="p">(</span><span class="n">content</span><span class="o">=</span><span class="n">trace_response</span><span class="o">.</span><span class="n">model_dump</span><span class="p">(</span><span class="n">by_alias</span><span class="o">=</span><span class="kc">True</span><span class="p">))</span> </code></pre></div> <p>Or set globally in FastAPI:</p> <div class="highlight"><pre><span></span><code><span class="n">app</span> <span class="o">=</span> <span class="n">FastAPI</span><span class="p">(</span><span class="n">generate_unique_id_function</span><span class="o">=</span><span class="k">lambda</span> <span class="n">route</span><span class="p">:</span> <span class="n">route</span><span class="o">.</span><span class="n">name</span><span class="p">)</span> <span class="c1"># Use response_model_by_alias=True per route, or override in app default</span> </code></pre></div> <p>Key points: - <code>populate_by_name=True</code> allows both <code>context_text</code> and <code>contextText</code> as input - <code>to_camel</code> from pydantic handles snake_case -&gt; camelCase automatically - Use <code>model_dump(by_alias=True)</code> when serializing for JSON response - Separate request (input) and response (output) models for flexibility</p>