&quot;create user&quot; request by calling the query that adds a new user to the database and returning the created id.</p><h2 id="handler"><a href="#handler" class="anchor"></a>Handler</h2><p>A &quot;handler&quot; is a function that is called on the Opium app in <code>app/main.ml</code> that specifies how the server responds to requests to different URLs with different request methods. Ice provides ways to automatically create handlers from controllers.</p><h2 id="migration"><a href="#migration" class="anc