title: How can i apply nested string operators in projection?
body: <p>I need to create an implementation using aggregator framework that executes this projection:</p>
  
  <pre><code>{ $project : { code: $toUpper : { $substr : ["$vendor", 0, 2 ] } } } 
  </code></pre>
  
  <p>So far I have not found a way to express the concatenation of the <code>$substr</code> and <code>$toUpper</code> operation using Spring. I have tried with this construction and other similar variants, but I have not succeeded.</p>
  
  <pre><code>ProjectionOperation projection = project()
                  .and("vendor").substring(0, 2).toLower().as("code");
  </code></pre>
  
  <p>Can anyone give me an idea of how to do this?</p>