title: How to convert a List<T> into a comma-separated list, using the class's Id property as the value
body: <p>I have a <code>List&lt;User&gt;</code> collection, and I want to create a comma seperated string using the User.Id property, so:</p>
  
  <pre><code>"12321,432434,123432452,1324234"
  </code></pre>
  
  <p>I have done it using a loop, but was hoping someone could show me the linq way?</p>