title: How to check if field is required in Doctrine?
body: <p>I wanna create and save an Entity from data passed through HTTP POST way.</p>
  
  <p>How can I enlist all the fields from an Entity that are required, so that my REST API method could check whether all required data have been passed through HTTP POST (to fulfill new created Entity), and send a response with an error if there are missing any (e.g. "There are missing fields which are required: "title", "message"...)?</p>