MongoDB Tutorial: Getting Started The Easy Way

What Is MongoDB?

MongoDB is a relatively recent non-relational database management system of the NoSQL variety. As ‘NoSQL’ implies, it doesn’t use SQL, and is a document store that utilizes key-value pairs similar to those in JSON. MongoDB stores data in the BSON format, which is reminiscent of JSON.

This condensed MongoDB tutorial will make it easy to get started with the MongoDB CLI easily. It also includes optional SQL notes for SQL users to pick it up even faster.

Table Of Contents

How To Install MongoDB In Ubuntu.
CRUD Operations (Create, Read, Update, Delete).
Read Operations.
Write Operations.
Update Operations.

Installing MongoDB On Ubuntu Linux

Repositories have made it easy to install MongoDB on Ubuntu and Debian. Just run these two commands:

sudo apt-get update
sudo apt-get install -y mongodb

Once the installation is complete, there are a number of security concerns and tweaks that are required for all databases (read more at the bottom).

You can now type sudo service start mongod, although it’s likely that it has already been started post-installation, and will automatically start with your computer in the future. You can shut down the MongoDB server by typing sudo service mongod stop.

‘Mongod’ is the Mongo daemon. That’s the server/DBMS. To use the MongoDB CLI, you just type ‘mongo’ at the Ubuntu command prompt and you should see a ‘>‘ or similar symbol show up in the terminal window (it is called the Mongo client).

That is the prompt at which you will type MongoDB commands, such as queries required to create databases, find records, write record to databases, and much more. You’ll need this tool to check for and delete/correct errors in databases every now and then.

MongoDB CRUD Operations

Let’s jump right into the creation of a database! (once you’ve started the mongo client), one of the most important aspects of this MongoDB tutorial. To create a database, you simply type use [databasename]. This command is also how you enter an existing database. Let us use the database name ‘mydb’ for this exercise.

use mydb

That’s it! Now you can insert a record. In MongoDB, that would be called a ‘document’. Documents contain key-value pairs, and are formatted as JSON objects. If you know JSON, that will be convenient, as that is what you’ll use to build your MongoDB queries. End your queries with a semicolon.

You can now insert a record in your MongoDB database (mydb) by typing the following:

db.fruits.insert({Name: 'Avocado', PotassiumContent: 708, ServingSize: 146});

This query inserts a document containing information about avocados into a collection called ‘fruits‘. A drawer of files pertaining to fruits is somewhat analogous to a MongoDB collection. The drawer can be considered the collection, and each file could be considered the document. Collections are automatically created using insert queries, so you don’t have to go create a collection beforehand.

Notes for SQL users

MongoDB doesn’t use tables, therefore I will provide little hints about what relates to what (no pun intended) with regards to MongoDB jargons so you can hit the ground running.

A collection is not the same as, but is the MongoDB equivalent of a table in SQL. A document is the equivalent of, but not the same as a row.

The SQL equivalent of the db.fruits.insert() command above is (the INSERT command is to be entered separately):

CREATE TABLE fruits (

name varchar(80),

potassiumcontent int,

servingsize int

);

INSERT INTO fruits VALUES('Avocado', 485, 100);

MongoDB Find Operations: Searching For A Record In A MongoDB Database

One way to find back our avocado record is to use the db.collection.find(); command as shown below.

db.fruits.find();

That command will find all documents (records) in the ‘fruits’ collection, because the brackets are empty. Currently, there is only one record in our fruits collection, and that’s fine for now. Let’s keep things short and simple until you get more comfortable with MongoDB.

You could have typed {Name: ‘Avocado’} between the brackets if you wanted to search only for documents with ‘Avocado’ in the name field.

The first (blank) MongoDB find query is equivalent to the following SQL query:

SELECT * FROM fruits;

MongoDB Write Operations

Now go ahead and enter some more fruits by typing the commands below. That’s called a MongoDB write operation. It makes for good practice, and we will update one of these records to make comparisons easier. Also remember that these commands must be typed at a Mongo client prompt. So if you closed the terminal window or exited the Mongo client, relaunch it.

db.fruits.insert({Name: 'Orange', PotassiumContent: 237, ServingSize: 131});

db.fruits.insert({Name: 'Kidney Beans', PotassiumContent: 405, ServingSize: 100});

MongoDB Update Operations

We now have three fruits in the database, but the serving size for the orange record is not the same as that of the other fruits. Therefore, we cannot do a fair comparison of these fruits/vegetables’ potassium content, because there is more orange than there is of the others.

To correct this we can update the record using the ‘$set‘ operator as shown below. Bear in mind that you need to use this instead of the ‘insert’ command, because the insert command will just create another record, resulting in duplicate documents.

db.fruits.update( {Name: 'Orange'}, { $set: {PotassiumContent: 181, ServingSize: 100} } );

You could do this in SQL by typing the following:

UPDATE fruits

SET potassiumcontent=181, servingsize=100

WHERE name=’Orange’;

Using The Greater Than Or Equal To Operator In MongoDB:

In MongoDB, there is a greater than or equal to operator ($gte) which you can use to display records containing fields which have a value greater than or equal to what you’re searching for. As an example, we will use the ‘$gte’ operator to find fruits which contain more than 200 mg of potassium, as shown below. I also squeezed in the optional ‘pretty()‘ function in the second example below to make the output less messy, as MongoDB’s output is generally jumbled. That is usually called ‘pretty printing’.

db.fruits.find({ PotassiumContent: {$gte: 200} });

Such a simple, short, yet useful command!

You can also use:

$gt: Greater than:

db.fruits.find({ PotassiumContent: {$gt: 200} }).pretty();

$lt: Less than:

db.fruits.find({ PotassiumContent: {$lt: 200} });

$lte: Less than or equal to:

db.fruits.find({ PotassiumContent: {$lte: 200} });

Notes for SQL users.

In SQL, you could use the ‘>‘ and ‘<‘ operators as shown in the example below.
SELECT * FROM fruits

WHERE potassiumcontent > 200;

How to create a new user in MongoDB and set their privileges

There are helpful tutorials explaining how to secure your MongoDB database server. They include, but are not limited to:

Managing Users And Their Permissions (must read)

Enabling Authentication (must read)

Configure MongoDB With Kerberos Authentication