title: Firestore exclude data serialization
body: <p>I've got several properties that should not be transferred to Firestore, such as metadata ("id" or "parent"), and with Firebase Realtime database, there was the option to set them to protected and make a getter to make them accessible to the outside world but not serialize to Firebase.</p>
  
  <p>With Firestore the only option to prevent a property from serialization is to create a class with a private property and extend that. But this is not really useful as the property is not even accessible from inside the class.</p>
  
  <p>Can you help me find a solution to create class properties that don't serialize to Firestore? (Maybe annotations?)</p>
  
  <p>Any help is greatly appreciated!</p>