Read file with node.js, mongoose, gridfs-stream

Question

I am using mongoose and gridfs-stream to store and read files from mongodb. I am following the example here: https://github.com/aheckmann/gridfs-stream

Writing files into db is working fine but I faced a problem to read files.

What the mongodb looks (show collections)

fs.chunks
fs.files

What the file index looks (db.fs.files.find())

{ "_id" : ObjectId("5140392659851df70b000001"), 
"filename" : "cover", 
"contentType" : "binary/octet-stream", 
"length" : 85734, 
"chunkSize" : 262144, 
"uploadDate" : ISODate("2013-03-13T08:30:30.299Z"), 
"aliases" : null, 
"metadata" : null, 
"md5" : "4476b26067daa0677978ba501308a35d" }

Then I use this code to get file named "cover"

...
var gfs = Grid(mongoose.connection.db, mongoose.mongo)
var readstream = gfs.createReadStream('cover')

An error occured:

Error: cover does not exist
at self.collection.self.fileId (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/gridfs/gridstore.js:198:26)
at Cursor.nextObject (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:654:35)
at Cursor.close (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:960:5)
at Cursor.nextObject (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:654:17)
at Cursor.nextObject.commandHandler (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:631:14)
at Db._executeQueryCommand (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:1702:5)
at g (events.js:185:14)
at EventEmitter.emit (events.js:115:20)
at Server.Base._callHandler (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/base.js:130:25)
at Server.connect.connectionPool.on.server._serverState (/mypath/node_modules/mongoose/node_modules/mongodb/lib/mongodb/connection/server.js:517:20)

I googled it and found some possible related links:

https://github.com/mongodb/node-mongodb-native/issues/621

Why gridfs get isn't working on file id (ObjectId) only by filename

Solution

The example code on GitHub was a little bit misleading; I initially received the same error message you did. In my case, it was due to the fact that I was attempting to read the file before the write stream had finished. I resolved this by doing the read inside the event handler for "close":

var fs = require("fs"),
    mongo = require("mongodb"),
    Grid = require("gridfs-stream"),
    gridfs,
    writeStream,
    readStream,
    buffer = "";

mongo.MongoClient.connect("mongodb://localhost/gridfs_test", function (err, db) {
    "use strict";
    gridfs = Grid(db, mongo);

    // write file
    writeStream = gridfs.createWriteStream({ filename: "test.txt" });
    fs.createReadStream("test.txt").pipe(writeStream);

    // after the write is finished
    writeStream.on("close", function () {
        // read file, buffering data as we go
        readStream = gridfs.createReadStream({ filename: "test.txt" });

        readStream.on("data", function (chunk) {
            buffer += chunk;
        });

        // dump contents to console when complete
        readStream.on("end", function () {
            console.log("contents of file:\n\n", buffer);
        });
    });
});