How to access a preexisting collection with Mongoose?

Question

I have a large collection of 300 question objects in a database test. I can interact with this collection easily through MongoDB's interactive shell; however, when I try to get the collection through Mongoose in an express.js application I get an empty array.

My question is, how can I access this already existing dataset instead of recreating it in express? Here's some code:

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

mongoose.connect('mongodb://localhost/test');
mongoose.model('question', new Schema({ url: String, text: String, id: Number }));

var questions = mongoose.model('question');
questions.find({}, function(err, data) { console.log(err, data, data.length); });

This outputs:

null [] 0

Weird

Answer 1

Mongoose added the ability to specify the collection name under the schema, or as the third argument when declaring the model. Otherwise it will use the pluralized version given by the name you map to the model.

Try something like the following, either schema-mapped:

new Schema({ url: String, text: String, id: Number}, 
           { collection : 'question' });   // collection name

or model mapped:

mongoose.model('Question', 
               new Schema({ url: String, text: String, id: Number}), 
               'question');     // collection name

Stutzman

Where in the docs can i find this information? This really helpped but there's no place explaining the plural thing. – Sawfly

Hi, @Stutzman how can I change the collection name at runtime? I have 5 collections of UserSchema and I want to give each one a different name Eg: users_server1, users_server2, users_server3... – Tanika

Pleae provide example query, e.g. with Model.collection.insert();.. – Barefoot

This does not help me. I have a collection called "widget_data" that I am trying to access (built somewhere else), but when I put var WidgetData = mongoose.model('WidgetData', new Schema(), 'widget_data'); then try to do WidgetData.find() it comes up with nothing. – Goggles

Same here, I spend many hours figuring out this issue, the document is found here mongoosejs.com/docs/guide.html#collection – Ansell

This worked for me. I had a users collection that I mongorestored. To get access to it with mongoose I did mongoose.connect("mongodb://localhost/fromlab"); var Schema = mongoose.Schema; var User = mongoose.model("User", new Schema({}), "users"); User.find({}, function(err, doc){ console.log((doc)) }) – Behlau

I tried the same @jack blank, but now i get a error saying Can not recompile already modelled data. :( – Humiliate

Answer 2

Here's an abstraction of Will Nathan's answer if anyone just wants an easy copy-paste add-in function:

function find (name, query, cb) {
    mongoose.connection.db.collection(name, function (err, collection) {
       collection.find(query).toArray(cb);
   });
}

simply do find(collection_name, query, callback); to be given the result.

for example, if I have a document { a : 1 } in a collection 'foo' and I want to list its properties, I do this:

find('foo', {a : 1}, function (err, docs) {
            console.dir(docs);
        });
//output: [ { _id: 4e22118fb83406f66a159da5, a: 1 } ]

Aristides

This is very helpful when running integration tests on an API – Minnesinger

hi, is this an atomic operation? Suppose I try to then save the document in the callback function. will this be atomic? – Morgue

Answer 3

You can do something like this, than you you'll access the native mongodb functions inside mongoose:

var mongoose = require("mongoose");
mongoose.connect('mongodb://localhost/local');

var connection = mongoose.connection;

connection.on('error', console.error.bind(console, 'connection error:'));
connection.once('open', function () {

    connection.db.collection("YourCollectionName", function(err, collection){
        collection.find({}).toArray(function(err, data){
            console.log(data); // it will print your collection data
        })
    });

});

---

Update 2022

If you get an MongoInvalidArgumentError: The callback form of this helper has been removed. error message, here's the new syntax using async/await:

const mongoose = require("mongoose");
mongoose.connect('mongodb://localhost/productsDB');

const connection = mongoose.connection;

connection.on('error', console.error.bind(console, 'connection error:'));
connection.once('open', async function () {

  const collection  = connection.db.collection("Products");
  collection.find({}).toArray(function(err, data){
      console.log(data); // it will print your collection data
  });

});

Trisyllable

I followed your solution, how do I get the data out of the async function? – Fictional

Answer 4

I had the same problem and was able to run a schema-less query using an existing Mongoose connection with the code below. I've added a simple constraint 'a=b' to show where you would add such a constraint:

var action = function (err, collection) {
    // Locate all the entries using find
    collection.find({'a':'b'}).toArray(function(err, results) {
        /* whatever you want to do with the results in node such as the following
             res.render('home', {
                 'title': 'MyTitle',
                 'data': results
             });
        */
    });
};

mongoose.connection.db.collection('question', action);

Rigorous

This is exactly what I was looking for because mongoose doesn't have any gridFS support. I use this method to grab file metadata from gridfs (gridstore). Just replace question in the code above with fs.files and you're good to go. – Mechanotherapy

Answer 5

Are you sure you've connected to the db? (I ask because I don't see a port specified)

try:

mongoose.connection.on("open", function(){
  console.log("mongodb is connected!!");
});

Also, you can do a "show collections" in mongo shell to see the collections within your db - maybe try adding a record via mongoose and see where it ends up?

From the look of your connection string, you should see the record in the "test" db.

Hope it helps!

Orthopsychiatry

Interesting, it's actually storing the information in a questions collection when the data I'm trying to access is in a question collection. Does Mongoose automatically pluralize collection/model names? – Weird

Yeah I think it does... ha! I'm just getting started myself so I haven't explored all the nooks and crannies... but I recall seeing that li'l chestnut breeze by as I was spinning through the Google Groups. – Orthopsychiatry

Answer 6

Something else that was not obvious, to me at least, was that the when using Mongoose's third parameter to avoid replacing the actual collection with a new one with the same name, the new Schema(...) is actually only a placeholder, and doesn't interfere with the exisitng schema so

var User = mongoose.model('User', new Schema({ url: String, text: String, id: Number}, { collection : 'users' }));   // collection name;
User.find({}, function(err, data) { console.log(err, data, data.length);});

works fine and returns all fields - even if the actual (remote) Schema contains none of these fields. Mongoose will still want it as new Schema(...), and a variable almost certainly won't hack it.

Bufflehead

it gives 'collection name must be string' error to me, Edit : as 'calvinfo' s answer, If you want to give collection name in model constructor you just pass the collection name in string form not object model. so your answer will be true if edit like this, var User = mongoose.model('User', new Schema({ url: String, text: String, id: Number}, 'users')); // collection name; User.find({}, function(err, data) { console.log(err, data, data.length);}); – Dimension

Answer 7

Go to MongoDB website, Login > Connect > Connect Application > Copy > Paste in 'database_url' > Collections > Copy/Paste in 'collection' .

var mongoose = require("mongoose");
mongoose.connect(' database_url ');
var conn = mongoose.connection;
conn.on('error', console.error.bind(console, 'connection error:'));
conn.once('open', function () {
  conn.db.collection(" collection ", function(err, collection){
    collection.find({}).toArray(function(err, data){
      console.log(data); // data printed in console
    })
  });
});

Alverta

Answer 8

I tried all the answers but nothing worked out, finally got the answer hoe to do it.

var mongoose = require('mongoose');
mongoose.connect('mongodb://0.0.0.0:27017/local');

// let model = require('./test1');

setTimeout(async () => {
  
    let coll = mongoose.connection.db.collection(<Your collection name in plural form>);
    // let data = await coll.find({}, {limit:2}).toArray();
    // let data = await coll.find({name:"Vishal"}, {limit:2}).toArray();
    // let data = await coll.find({name:"Vishal"}, {projection:{player:1, _id:0}}).toArray();
    let data = await coll.find({}, {limit:3, sort:{name:-1}}).toArray();
    console.log(data);
    
}, 2000);

I have also mentioned some of the criteria to filter out. Delete and update can also be done by this.

Thanks.

Fumatorium

Answer 9

If you are using a modern version of Mongoose, you can try this solution without specifying a schema:

    const result = await mongoose.connection.db.collection('COLLECTION_NAME').find().toArray()

Don´t use the old callback function:

mongoose.connection.db.collection(name, function (err, collection) { ... })

Will get this error: "The Callback form of this helper has been removed."

Louls

Answer 10

Make sure you're connecting to the right database as well as the right collection within the database.

You can include the name of the database in the connection string.

notice databasename in the following connection string:

var mongoose = require('mongoose');
const connectionString = 'mongodb+srv://username:[email protected]/databasename';

mongoose.connect(connectionString);

Isolde

and how to declare the right collection name? – Hafer

Answer 11

//access-a-preexisting-collection-with-mongoose
const express = require('express');
const mongoose = require('mongoose');

const app = express();

// Define your MongoDB URI
const MONGO_URI = "mongodb://localhost:27017/chat_history";

// Connect to MongoDB
mongoose.connect(MONGO_URI});

// Define a Mongoose schema (if necessary)
// const YourSchema = new mongoose.Schema({
//   // Define schema fields here
// });

// Define a Mongoose model (if necessary)
// const YourModel = mongoose.model('YourModel', YourSchema);


app.get('/transcript', async (req, res) => {
  try {
    // Access the collection
    const collection = mongoose.connection.db.collection("message_store");

    // Query the collection for transcripts with a specific SessionId
    const cursor = collection.find({ SessionId: req.query.session_id });

    // Convert the cursor to an array of documents
    const transcripts = await cursor.toArray();

    // Respond with the transcripts
    res.json(transcripts);
  } catch (error) {
    console.error(error);
    res.status(500).json({ message: "Internal server error" });
  }
});

// Start the server
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Dina