Indexing in MongoDB

Welcome to a tutorial on Indexing n MongoDB.

Indexes in SQL programming are special data structures used to easily and quickly locate the record in a given table of the database without being required to traverse through each and every record of the table.

Also, indexes are easily generated by making use of one or more columns of a given table. Note that the data structure used by an index is a Binary Tree (B-Tree).

Indexes play an important role in the efficient execution of the queries in MongoDB. Typically, if no index is defined in MongoDB, then it has to scan all the documents of a given collection. So, an index is used by MongoDB to reduce the number of documents to be scanned in a given collection. 

More importantly, MongoDB's index is quite similar to the indexes used in other relational databases. Also, it defines the indexes at the collection level and supports indexing on any fields in a MongoDB collection.

Default Index in MongoDB

A default index named _id is provided by MongoDB, which acts as a primary key to access any document in a collection. This _id index avoids the insertion of 2 documents with the same value for the _id field.

Creating an Index using createIndex()

Run the command below to create an index in MongoDB.

db.collection_name.createIndex({field : value })

Now, to create an index on the field regNo for a student collection, run this command db.student.createIndex({regNo : 1})

The output of this command is shown below.

 {
"createdCollectionAutomatically": false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}

Also, we can create Index on multiple fields by running a single command: db.student.createIndex({regNo : 1, address : -1})

Types of Indexes in MongoDB

Therefore, having all these features, index management is an important and central part of the MongoDB application.