MongoDB Administrator's Guide

How to do it...

1. Check the total number of documents in our collection and number of documents without the language field:

db.mockdata.count()

The preceding command should return 100000:

db.mockdata.find({language: {$eq:null}}).count()

The preceding command should return 12704.

2. Create a sparse index on the document:

> db.mockdata.createIndex( {first_name:1}, {partialFilterExpression: { language: {$exists: true}}})

This should give you output similar to this:

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

3. Confirm that the index was created:

db.mockdata.getIndexes()

The preceding command should give you output similar to this:

[  {    "key": {      "_id": 1    },    "name": "_id_", "ns": "mydb.mockdata", ...