title: How to filter out certain documents in a firestore query
body: <p>I'm looking to implement a friends search function in my social app. For this I try to query for every user's document in the <code>users</code> collection of the DB, but it should exclude some specific documents like users who the current user is already friends with or request pending.</p>
  <p>Is it possible to query for all the users documents, excluding specific documents by passing those documents reference ID's in Firestore.</p>
  <p>If not, can somebody say a way to structure the data so that I can implement this functionality. Thanks.</p>