title: Get required fields from Document in mongoengine?
body: <p>I want to be able to get a list or some sort of set of fields that are required by the document i've created. For instance, here is my document:</p>
  
  <pre><code>nickName        = StringField(required=True)
  password        = StringField(required=True)
  firstName       = StringField()
  lastName        = StringField()
  joinDate        = DateTimeField(required=True)
  lastVisited     = DateTimeField(required=True)
  subscriptions   = DictField(field=ObjectIdField())
  isActivated     = BooleanField(default=True)
  profileImage    = FileField()
  isModerator     = BooleanField(default=False)
  description     = StringField()
  location        = GeoPointField()
  email           = EmailField()
  settings        = DictField()
  </code></pre>
  
  <p>^From this document I should receive:</p>
  
  <pre><code>["nickName","password","joinDate","lastVisited"]
  </code></pre>
  
  <p>as results for being required fields. Is this possible? If so, how can I achieve the desired result.</p>
  
  <p>Thanks in advance!</p>