MongoDB database can perform all types of CRUD (Create, Read, Update, Delete) operations. We use a module called mongoose to connect to the MongoDB database.

In the above code, we have connected our project to the MongoDB database. After that we have created a schema, which defines the structure of the data going to be stored. Then we have created a model and exported that to use in the other parts of the application.

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If you have already installed MongoDB.

If Not go-ahead download from here

var MongoClient = require('mongodb').MongoClient;
//Create a database named "testdb":
var url = "mongodb://localhost:27017/testdb";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  console.log("Database created!");
  db.close();
});

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Instead of going page by page in a Book one can get to any Topic by searching on the index.

In MongoDB, these indexes are made of btree. These btree orders the Documents and guide to the required one with a far lesser read operation.

But all this speed doesn’t come for free. Writing operations are inversely proportional to the number of indexes in a DB.

More the indexes more the need to balance them on every write.

Types of indexes:-

• Single Field Index

As the name suggests these are comprised of a single field. This is the simplest form of an index.

db.your_collection.createIndex(
		 { 
		 	field_to_be_indexed: 1 
		 } 
		)

NOTE:- 1 at the end of the command is to index in ascending order.

• Compound Index

The compound index is those index containing more than one fields. In this type of index, order plays an important role as Mongo Db will create Index in Orderly fashion.

db.your_collection.createIndex(
		 { 
		 	first_field_to_be_indexed: 1, 
		 	second_field_to_be_indexed: 1 
		 } 
		)

• Multikey Index

It is an advanced version of the compound index as it can contain array values of subfields in a document. That too multiple of them

db.your_collection.createIndex(
		 { first_field_to_be_indexed: 
		 	[
		 		field1: 1, 
		 		field2: 1
		 	]
		 } 
		)

Multikey indexes are most Complex and needed to execute with utmost precaution as this index can lead to a large index file which can harm the operation of writing anything.

There is more type of indexes that we will talk about in the next part.

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