How to create a nested index in MongoDB?

To create nested index in MongoDB, you can use createIndex() or ensureIndex(). The syntax is as follows −

db.yourCollectionName.createIndex({"yourOuterFieldName.yourInnerFieldName.yourSecondInnerFieldName": 1});

To understand the syntax, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.nestedIndexDemo.insertOne(    ... {       ...       ... "CustomerId":101,       ... "CustomerDetails":       ... {          ... "CustomerListDetails":          ... {             ... "CustomerName":"Larry",             ... "CustomerProjectName": "Project-1",             ... "CustomerCountryName":"US"          ... }       ... }    ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5c8fc565d3c9d04998abf010") }

Display all documents from a collection with the help of find() method. The query is as follows −

> db.nestedIndexDemo.find().pretty();

The following is the output −

{    "_id" : ObjectId("5c8fc565d3c9d04998abf010"),    "CustomerId" : 101,    "CustomerDetails" : {       "CustomerListDetails" : {          "CustomerName" : "Larry",          "CustomerProjectName" : "Project-1",          "CustomerCountryName" : "US"       }    } }

Here is the query to create a nested index in MongoDB:

> db.nestedIndexDemo.createIndex({"CustomerDetails.CustomerListDetails.CustomerCountryName": 1}); {    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }

Here is the query to display index −

> db.nestedIndexDemo.getIndexes();

The following is the output −

[    {       "v" : 2,       "key" : {          "_id" : 1       },       "name" : "_id_",       "ns" : "test.nestedIndexDemo"    },    {       "v" : 2,       "key" : {          "CustomerDetails.CustomerListDetails.CustomerCountryName" : 1       },       "name" : "CustomerDetails.CustomerListDetails.CustomerCountryName_1",       "ns" : "test.nestedIndexDemo"    } ]