Create Causal Consistency code samples for MongoDB 3.6 page

// 2. Tunable consistency controls

String connectionString = "mongodb://localhost/?readPreference=secondaryPreferred";

MongoClient client = new MongoClient(new MongoClientURI(connectionString);

MongoDatabase database = client.getDatabase("myDatabase");

MongoCollection<Document> collection = database.getCollection("myCollection");

// Start client session, which is causally consistent by default

try (ClientSession session = client.startSession(ClientSessionOptions.builder().build())) {

  //Run causally related operations within the session

  collection.insertOne(session, ...);

  collection.updateOne(session, ...);

  try (MongoCursor<Document> cursor = collection.find(session).filter(...).iterator()) {

    while (cursor.hasNext()) {

      Document cur = cursor.next();

    }

  }

}