Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Node.js - Mongoose - Check if a collection exists

I need to insert some data using mongoose but the name of the collection is provided by the user at the moment of the insertion, so I first have to check if the collection exists.

The way I know how to check if a collection exists is by querying the system.namespaces collection. I can see 3 possible approaches to doing that.

  1. Find a way to query system.namespaces using mongoose (maybe defining a schema that matches the one in the db).
  2. Getting some underlying node-mongodb-native object from mongoose and performing the query manually. In any case, this is something I would like to learn how to do.
  3. Using a separate instance of a node-mongodb-native (or some other driver) to perform the query

Number 3 is the least elegant and the one i'm trying to avoid, I don't want to load another instance of the driver nor create a new connection when mongoose already created one.

I'm going to try number 1 after writing this. I just checked system.namespaces and the schema looks quite simple

I'd still like to hear some opinions.

Thanks!

like image 765
Juan Campa Avatar asked Nov 18 '12 21:11

Juan Campa


People also ask

How to check if collection exists in MongoDB Nodejs?

The collectionExists method can be used to check whether a collection is present or not: MongoClient mongoClient = new MongoClient("localhost", 27017); DB db = mongoClient. getDB("baeldung"); String testCollectionName = "student"; System.

Is exist in mongoose?

What is exists() in Mongoose? exists is a Mongoose method or function that is used to check if at least one document exists that matches a specified filter. If there is a match, true is returned. Otherwise, false is returned.

Does MongoDB Create collection if not exists?

If a collection does not exist, MongoDB creates the collection when you first store data for that collection. You can also explicitly create a collection with various options, such as setting the maximum size or the documentation validation rules.

Does Mongoose model create collection?

Mongoose by default does not create any collection for the model in the database until any documents are created. The createCollection() method is used to create a collection explicitly.


2 Answers

Option 2 is probably the cleanest. Assuming you have a Mongoose Connection object named conn that's been opened using mongoose.createConnection, you can access the native mongo Db object via conn.db. From there you can call collectionNames which should provide what you're looking for:

conn.db.collectionNames(function (err, names) {     // names contains an array of objects that contain the collection names }); 

You can also pass a collection name as a parameter to collectionNames to filter the results to just what you're looking for.

Mongoose 4.x Update

In the 2.x version of the MongoDB native driver that Mongoose 4.x uses, collectionNames has been replaced by listCollections which accepts a filter and returns a cursor so you would do this as:

mongoose.connection.db.listCollections({name: 'mycollectionname'})     .next(function(err, collinfo) {         if (collinfo) {             // The collection exists         }     }); 
like image 146
JohnnyHK Avatar answered Sep 22 '22 02:09

JohnnyHK


This works for me (mongoose version 5.1.1):

const mongoose = require('mongoose'); const mongoURI = 'mongodb://localhost:27017/mydb' // notice the mongoose.createConnection instead of mongoose.connect const conn = mongoose.createConnection(mongoURI); conn.on('open', function () {     conn.db.listCollections().toArray(function (err, collectionNames) {       if (err) {         console.log(err);         return;       }         console.log(collectionNames);         conn.close();     }); }); 
like image 40
V. Lipunov Avatar answered Sep 21 '22 02:09

V. Lipunov