Reusing gridfs with mongoose

I'm using gridfs-stream with mongoose. The docs say to connect using:

var conn = mongoose.createConnection();
conn.once("open", function () {
    var gfs = Grid(conn.db, mongoose.mongo);
});

I assume that it's preferred to reuse one Grid (gfs above) throughout the app. (True?) Accordingly, I have a module gridfs.js containing

module.exports = Grid(mongoose.connection.db, mongoose.mongo);

which, relying on node's module caching, will reuse the Grid. However, my main file (app.js) is structured like this:

app.use("/path1", require("controllers/path1.js"));
// ...
mongoose.connect(...);
mongoose.connection.once("open", function () {
    app.listen(port);
});

Issue is: the controller required on the first line of the snippet has a require("gridfs.js") line, and that comes before mongoose connects.

Questions:

• 
  

  Is it proper to reuse a Grid throughout an app, or should I create one in each route handler? (Note that it would have to be in the route handler callback itself, not at the top of the module, for the above reason.)

  
  


• 
  

  If reuse is proper, what's the right way to fix the above problem? Load all my routes/controllers in the mongoose.connection.once("open") callback?