Funguje to pro mě na příkladu níže
run () ->
application:start (mongodb),
{ok, Conn} = mongo:connect (localhost),
{ok, Docs} = mongo:do (safe, master, Conn, test, fun() ->
mongo:delete (foo, {}),
mongo:insert_all (foo, [{x,1}, {x,2}, {x,3}, {x,0}, {x,-1}]),
Cur = mongo:find (foo, {'$query', {}, '$orderby', {x,1}}, {'_id',0}, 0, 3),
mongo:rest (Cur) end),
mongo:disconnect (Conn),
[{x,-1}, {x,0}, {x,1}] = Docs.