You can use dot(.) notation for this. Let us first create a collection with documents −
> db.createIndexOnNestedFieldDemo.insertOne( {"UserDetails":{"UserPersonalDetails":{"UserFirstName":"John","UserLastName":"Smith"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5ce929c778f00858fb12e916") } > > db.createIndexOnNestedFieldDemo.insertOne( {"UserDetails":{"UserPersonalDetails":{"UserFirstName":"Chris","UserLastName":"Brown"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5ce929d678f00858fb12e917") } > db.createIndexOnNestedFieldDemo.insertOne( {"UserDetails":{"UserPersonalDetails":{"UserFirstName":"David","UserLastName":"Miller"}}}); { "acknowledged" : true, "insertedId" : ObjectId("5ce929e378f00858fb12e918") }
Following is the query to display all documents from a collection with the help of find() method −
> db.createIndexOnNestedFieldDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5ce929c778f00858fb12e916"), "UserDetails" : { "UserPersonalDetails" : { "UserFirstName" : "John", "UserLastName" : "Smith" } } } { "_id" : ObjectId("5ce929d678f00858fb12e917"), "UserDetails" : { "UserPersonalDetails" : { "UserFirstName" : "Chris", "UserLastName" : "Brown" } } } { "_id" : ObjectId("5ce929e378f00858fb12e918"), "UserDetails" : { "UserPersonalDetails" : { "UserFirstName" : "David", "UserLastName" : "Miller" } } }
Following is the query to create an index on a nested field −
>db.createIndexOnNestedFieldDemo.createIndex({"UserDetails.UserPersonalDetails.UserLastName":1});
This will produce the following output −
{ "createdCollectionAutomatically" : false, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 }