MongoDB - Indexes

#explain command 
pp db[:zips].find(:state => 'MD').explain

#List all indexes:

db[:zips].indexes.each do |index| 
p index 

#drop_one 
db[:zips].indexes.drop_one('state_1')

#unique command 

db[:users].indexes.create_one({ "user_id":1}, {unique: true})

#sparse index 
db[:users].indexes.create_one({ "user_id:1}, { sparse: true})

#TTL index 
db[:users].indexes.create_one({ "user_id:1}, { expireAfterSeconds: 3600})