Lesson 1
Last Updated : February, 2023

What is a Mongo Database?

MongoDB is a popular open-source document-oriented NoSQL database that is designed to store and manage large volumes of data. It was developed by MongoDB Inc. and first released in 2009. MongoDB is written in C++, and it provides a flexible and scalable data model that allows developers to easily store and query data in a JSON-like format.

One of the key features of MongoDB is its ability to scale horizontally across multiple servers. MongoDB achieves this through a process called sharding, which allows data to be distributed across multiple servers to improve performance and reduce the risk of data loss.

Another feature of MongoDB is its powerful query language, which supports a wide range of operations and data types. MongoDB also supports full-text search, geospatial queries, and graph processing.

To work with MongoDB, developers typically use a MongoDB driver or an object-document mapping (ODM) tool that provides a high-level interface for working with the database. Some popular MongoDB drivers and ODMs include the official MongoDB driver for various programming languages such as Python, Java, and C#, as well as Mongoose for Node.js, and PyMongo for Python.

Overall, MongoDB is a powerful and flexible NoSQL database that is popular with developers due to its scalability, performance, and ease of use.

The Collections

In MongoDB, a collection is a group of documents. A document is similar to a row in a traditional relational database table. However, unlike a table, a document can have a flexible schema and can contain nested data structures.

In MongoDB, collections are analogous to tables in a relational database, and documents are analogous to rows in a table. Collections are created when the first document is inserted into the collection. The schema for a collection is not enforced, meaning that each document in the collection can have different fields and field values.

Here’s an example of how to create a collection in MongoDB using the Mongo Shell:

> use mydb
switched to db mydb

> db.createCollection("mycollection")
{ "ok" : 1 }

This creates a new collection called mycollection in the mydb database. Once the collection is created, you can insert documents into it using the insert() method:

> db.mycollection.insert({ name: "John", age: 30 })
WriteResult({ "nInserted" : 1 })

This inserts a new document into the mycollection collection with the fields name and age. You can also retrieve documents from the collection using the find() method:

> db.mycollection.find()
{ "_id" : ObjectId("60a0f9c2e57b4307aae5483c"), "name" : "John", "age" : 30 }

This retrieves all documents from the mycollection collection, which in this case is just one document.

Overall, collections in MongoDB provide a flexible way to store and retrieve data, allowing for dynamic and scalable data models.

The Documents

In MongoDB, data is stored as documents in collections. A document is a set of key-value pairs, where the keys are strings and the values can be any valid JSON data type, including strings, numbers, Booleans, arrays, and other nested objects.

For example, here’s a sample document representing a user in a user collection:

  "_id": ObjectId("60f12fbbf99c2d6e1b6e7e81"),
  "name": "John Doe",
  "email": "",
  "password": "password123",
  "age": 30,
  "is_verified": true,
  "created_at": ISODate("2021-07-15T14:03:23.840Z")

In this document, we have several key-value pairs:

_id: A unique identifier for the document. This is automatically generated by MongoDB if not provided explicitly.

name, email, password: String values representing the user’s name, email, and password.

age: A number representing the user’s age.

is_verified: A Boolean value indicating whether the user’s email has been verified.

created_at: A date and time value indicating when the document was created.

Documents in MongoDB can have nested structures as well. For example, here’s a document representing a blog post:

  "_id": ObjectId("60f13024f99c2d6e1b6e7e82"),
  "title": "My First Blog Post",
  "content": "Lorem ipsum dolor sit amet, consectetur adipiscing elit...",
  "author": {
    "name": "John Doe",
    "email": "",
    "website": ""
  "comments": [
      "name": "Jane Smith",
      "email": "",
      "comment": "Great post! Thanks for sharing."
      "name": "Bob Johnson",
      "email": "",
      "comment": "I disagree with your points. Here's why..."
  "created_at": ISODate("2021-07-15T14:10:12.780Z")

In this document, we have several key-value pairs:

_id: A unique identifier for the document.

title, content: String values representing the title and content of the blog post.

author: A nested document representing the author of the post, with name, email, and website fields.

comments: An array of nested documents representing comments on the post, with name, email, and comment fields.

created_at: A date and time value indicating when the document was created.


Schemaless in the context of MongoDB means that there is no fixed schema or structure that needs to be followed when creating documents in a collection. Unlike in a traditional relational database where the schema needs to be defined beforehand, in MongoDB, you can create documents with different fields and field types without any pre-defined structure.

This flexibility in schema design allows for easy and agile development, as the data model can be easily adapted to changing requirements. It also allows for efficient storage of heterogeneous data, as each document can have a unique set of fields and data types.

However, this also means that data validation and consistency need to be handled programmatically or through the use of tools like validators, as there is no built-in mechanism to enforce data consistency or integrity. It is also important to maintain consistency in field names and data types across documents to ensure efficient querying and indexing.

Limitations of Relational databases

Relational databases have been the go-to solution for storing and managing data for several decades, but they also have some limitations. Here are some of the limitations of relational databases:

  • Difficulty handling unstructured or semi-structured data: Relational databases are designed to store structured data in tables with predefined schemas. They are not well-suited to handling unstructured or semi-structured data such as text, images, videos, and audio.

  • Scalability issues: Relational databases are not easily scalable horizontally, meaning that adding more nodes to increase capacity can be difficult and require significant effort. This can limit the ability to handle large amounts of data.

  • Cost: The cost of setting up and managing a relational database can be significant, especially for large-scale applications.

  • Performance issues: The performance of relational databases can degrade as the amount of data grows, and queries become more complex. Indexing can help improve performance, but it can also increase the complexity of managing the database.

  • Data redundancy: Relational databases often require a lot of data duplication to maintain the integrity of the data, which can lead to issues with data consistency and increased storage requirements.

  • Limited support for distributed computing: Traditional relational databases are not well-suited to distributed computing, making it difficult to take advantage of the performance benefits of distributed systems.

These limitations have led to the development of alternative database systems, such as NoSQL databases, which are designed to address some of these issues.

What are the advantages of NoSQL

NoSQL databases offer several advantages over traditional relational databases, including:

  • Scalability: NoSQL databases are designed to handle large amounts of unstructured data and can be scaled horizontally across multiple servers, allowing for easier scaling as data grows.

  • Flexibility: NoSQL databases are schema-less, meaning they don’t require a fixed schema or data model. This allows for greater flexibility in handling data and makes it easier to adapt to changing requirements.

  • Performance: NoSQL databases are optimized for fast read/write operations and can handle high volumes of data with low latency.

  • Cost-effectiveness: NoSQL databases are often open source, making them more cost-effective than traditional relational databases that require expensive licensing fees.

  • Availability: NoSQL databases are designed to provide high availability and can be configured for fault tolerance and disaster recovery.

  • Agility: NoSQL databases allow for rapid development and deployment of new applications and features due to their flexible data model and scalability.

Overall, NoSQL databases are a good fit for modern applications that require high scalability, flexibility, and performance with large amounts of unstructured data.