eolas/Databases/MongoDB/Introduction.md

---
tags:
- Databases
- mongo_db
---

# MongoDB: Introduction

MongoDB is not a relational database system like SQL, instead it is document-based which means you do not neeed to design database tables and schema, you are simply storing data as JSON and there is no transformation of the data. 

Most of the notes on Mongo will introduce it within the context of Node.js backend. We will be sending Javascript objects and arrays to Mongo and returning them as JSON. 

## Setting-up a MongoDB database

First create a directory for the database and set permissions:
```bash
$ mkdir /data/db
$ sudo chown -R `id -un` /data/db
```

Then start the Mongo daemon
```bash
mongod
```
This will run continuously in the terminal and should say somewhere that it is waiting for connections on port 27017. This command must be used before you run any backend that interacts with the Mongo database. 
### MongoDB Compass
_Compass_ is a graphical interface for viewing and interacting with the data in your Mongo database. It will automatically load to the default Mongo port: 27017.

![](/img/mongo-compass.png)

### Arch Linux troublshooting
```bash
# Check that the systemd service is runnign for Mongo
sudo systemctl status mongodb

# If not, enable and start service (only need to do this once for machine)
sudo systemctl enable --now mongodb
sudo systemctl start --now mongodb

# If issues with Mongo daemon...
# Remove the current socket
rm mongodb-27017.sock

# Kill running Mongo process...
# Identify PID
sudo lsof -iTCP -sTCP:LISTEN -n -P
sudo kill [pid]
```

## Mongoose 

Now that we have installed and configured MongoDB, we need to connect from it via Node.js.Mongoose is a simple API for interacting with a Mongo database via Node.

With this installed we can connect to a database. We don't have any Mongo databases yet beyond the defaults but the following Mongoose connection logic will create and connect to a new database called `playground`:

```js
mongoose
  .connect("mongodb://127.0.0.1/playground")
  .then(() => console.log("Connected to MongoDB"))
  .catch((err) => console.error(err));
```