title: what is the best way to manage FCM registration ID in database server?
body: <p>I'm trying to use firebase cloud messaging service for my android application and I'm trying to find the best way to manage registration ID in database server.
  I was thinking to create new table with <code>userID,registrationId</code> (where userID is unique for each user) in my database and insert new record once the user logs in successfully and remove that record when the user logs out. but there are some situation that the registration Id will be refreshed, I can get the new registration Id to save it in the database. but how can I get the old registration Id to remove it?</p>
  
  <p>Are there better way to manage the registration Id in database?</p>
  
  <p>note: a device can access one account but there are might be many devices that use the same account.</p>