title: multiple routes with differents params, calling the same ressource
body: <p>Is it possible with expressjs to have multiple routes calling the same resource, something like that:</p>
  
  <pre><code>app.get('/users/:user_id', users.getOne)
  app.get('/users/:username', users.getOne)
  </code></pre>
  
  <p>I would like to be able to call users.getOne whichever params (:user_id or :username) is used in the get request.</p>
  
  <p>In the users.getOne function, how can I determine wich one was used and build my query according to it?</p>
  
  <pre><code>exports.getOne = function(req, res){
  
    var queryParams = ? // I need help here
  
    Users
      .find(queryParams)
      ...
  </code></pre>
  
  <p>Thanks!</p>
  
  <p>Possibly related: <a href="https://stackoverflow.com/questions/15350025/multiple-routes-single-function-call-express-js">express.js - single routing handler for multiple routes in a single line</a></p>