Working With Databases In MongoDB

Introduction

In this article, we will learn about Databases in MongoDB. If you are new to MongoDB, then I would recommend you go through the previous articles in this series.

• Part 1 -How To Set Up And Start With MongoDB
• Part 2 -Configure A Windows Service For MongoDB

Before starting, let’s see the terminologies we are going to use frequently in this write-up, as well as in the upcoming articles, of this series.

• A field is a name-value pair and its concept is much similar to the Columns of RDBMS.
• The document follows the JSON syntax known as BSON and it's quite similar to the Rows in RDBMS.
• A collection is a group of documents in MongoDB and it is similar to the Tables in RDBMS.
• A Database is a container for all the collections and a single node of MongoDB Server can store multiple databases.

In RDBMS, we use joins in order to get the data from the multiple tables, whereas in MongoDB, the data is stored in a single collection but separated by Embedded Documents.

Before creating a database, we need to connect the MongoDB Client with the use of a Mongo Shell command. We already saw how to do that in the previous article of the series.

Let’s begin.

db Command

The db command is used for checking the currently selected database. By default, it shows you the test database as the selected database.

show dbs

The show dbs command shows you the database list available on MongoDB.

There are several database names that are reserved and will be shown initially.

1. admin: If a user is added to the admin database, then the added user automatically inherits permission to access all the databases and also, helps to run the commands that can only run from the admin database.-
2. local: A local database stores data used in the replication process. In replication, the local database stores internal replication data for each member of a replica set.-
3. config

Usage

The use command is used to create a new database if the database does not exist. And if it exists, then it will select the existing database.

In the above example, we created a new database, i.e., MongoDB tutorial, and after that, checked the active or currently selected database. But still, if you try to check the database list using the show dbs command, you will not be able to see the MongoDB tutorial database as we have not added any collection in that base. Now, add a collection (we will learn more about the collection, in-depth, in the next article of the MongoDB series). We can add collection in a database with the use of the createDatabase() method which accepts the name of the database as a parameter. After adding a collection, the database will be shown in the database list.

dropDatabase()

In MongoDB, we can drop the database with the help of the dropDatabase() method. Before dropping the database, make sure that you have selected the right database with the db command. As, for example, we first checked the selected database and then dropped it with the dropDatabase() method.

Hope this will help you.

Thanks.