How can I specify a GridFS bucket?

Question

This is my express.js code to upload and download files to GridFS:

var fs = require("fs");
var gridStream = require("gridfs-stream");
var mongoose = require("mongoose");

exports.init = function(app, db)
{
    var grid = gridStream(db, mongoose.mongo);

    app.post("/UploadFile", function(request, response)
    {
        var file = request.files.UploadedFile;

        var meta = request.param("Meta");
        var name = request.param("Name");

        var stream = grid.createWriteStream(
        {
            filename: name,
            metadata: meta
        });

        fs.createReadStream(file.path)
        .on("end", function()
        {
            response.send({ Success: true });
        })
        .on("Error", function(error)
        {
            HandleError(error, response);
        })
        .pipe(stream);
    });

    app.get("/DownloadFile", function(request, response)
    {
        var selector = request.param("Selector");

        response.writeHead(200, { "Content-Type" : "image/png"});
        grid.createReadStream({ filename: "FileUploadNamed" }).pipe(response);
    });
}

It works perfectly, but I'd like to specify a bucket to read and write from, but I'm not sure how to do that. I've seen examples online calling a GridFS constructor, but as you can see I'm not doing that here. The documentation also says that it's possible to supply a different bucket name, but I don't see anything on how.

How can I select which bucket that my files are saved to and read from?

Answer 1

This is not well documented in gridfs-stream or the underlying native mongodb driver it uses, but here is how you do it:

Here is the options object from the gridfs-stream createWriteStream example (note the root option):

{
   _id: '50e03d29edfdc00d34000001', 
   filename: 'my_file.txt',         
   mode: 'w', 
   chunkSize: 1024, 
   content_type: 'plain/text', 
   root: 'my_collection',  // Bucket will be 'my_collection' instead of 'fs'
   metadata: {
       ...
   }
}

Why it works:

gridfs-stream passes through the options object you pass a call to createWriteStream or createReadStream to the underlying mongodb driver to create a gridStore object to represent the file. The mongodb driver in turn recognizes root in the options object as an override of the default "fs" grid bucket prefix string.