anchor.diff:  do_create_server(#state{topology = Topology}, Rec) ->
       Map = to_map(server, Rec),
       Callback = fun(Worker) ->
  -                       mc_worker_api:insert(Worker, ?COLLECTION_SERVERS, Map)
  +                       mc_worker_api:insert(Worker, ?COLLECTION_SERVER, Map)
                  end,
       Item = mongoc:transaction(Topology, Callback),
       do_create_result(Item, server).
  
positive.code:                        Key = #{<<"_id">> => id_to_objectid(Rec#server.id)},
                         Command = #{<<"$set">> => maps:remove(<<"_id">>, Map)},
                         {
                           mc_worker_api:update(Worker, ?COLLECTION_SERVERS, Key, Command),
                           mc_worker_api:find_one(Worker, ?COLLECTION_SERVERS, Key)
                         }
                 end,
      {Res, ResMap} = mongoc:transaction(Topology, Callback),
  
negative.code: 
  do_get_server(#state{topology = Topology}) ->
      Callback = fun(Conf) ->
                         mongoc:find_one(Conf, ?COLLECTION_SERVER, #{}, #{}, 0)
                 end,
      Item = mongoc:transaction_query(Topology, Callback),
      do_get_result(Item, server).
  