mongodb - How can I get a native driver database context with Mongoose?

Question

I'm using Mongoose, and I'd like to use the native driver for some things. One of the things I'd like to do is make a query for a GridFS file. You normally do that as such:

db.fs.files.findOne({});

However, mongoose.connection.db doesn't have fs defined. So I need a native driver db object, not the Mongoose one. Is there a way that I can get such an object from Mongoose?