Common MongoDB and Mongoose Pitfalls

And their solutions

MongoDB and Mongoose are commonly used with Node JS projects. In this article, you’ll find a small list of pitfalls that can be easily avoided and save you hours of debugging time.

If you are new to Mongo and Mongoose, I highly recommend the Mongoose quick start guide:

Mongoose Quick Start v4.10.8

Everything in this article will be loosely based on the examples given in the quick start guide.

Pitfall #1: Overthinking the guide

When reading the quick start guide, adding a kitten named ‘Silence’ feels like creating a new collection instead of inserting a document into the kitten collection.

So this:

var silence = new Kitten({ name: 'Silence' });

creates a new document, not a new collection.

Pitfall #2: Remember to save

It’s easy to do this:

var fluffy = new Kitten({ name: 'fluffy' });

But forget about doing this:

fluffy.save(function (err, fluffy) {   
  if (err) return console.error(err);   
  fluffy.speak(); 
});

If you ever have trouble finding your version of fluffy in the collection, check if you have saved it first.

Pitfall #3: MongoDB connection error when starting a new project

When this problem occurs, there is a high possibility that you still have mongod running for your previous project which is creating a conflict.

The error message may look something like this:

npm ERR! code ELIFECYCLE
npm ERR! errno 48
npm ERR! <file location> db-start: `mongod --dbpath ./database/data/db`
npm ERR! Exit status 48
npm ERR!
npm ERR! Failed at the <file location> db-start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

Go to your project folder in the terminal and type this:
(press enter after each line)

mongo
use admin
db.shutdownServer()

Pitfall #4: db.collection.find()

The ‘.find()’ returns every line in the specified collection. Here’s an example:

1. You have a db called ‘test’
2. Inside ‘test’, you have a collection called ‘items’

If you want all the data inside items, type this into terminal:
(press enter after each line)

mongo
use test
db.items.find()

and these do not work:

test.items.find()
items.find()

Other useful tips

When testing: use db.dropDatabase() to delete the entire database after testing connections, schemas, or after you finished testing.

Creating a database: after you have defined a new schema and model, a new database is automatically created after you insert the first document into the schema. Don’t waste your time looking for how to create a new database.

Other helpful resources: The official Mongoose Docs and MongoDB docs are quite handy in solving most of the problems that you might have.