working with indexes in mongo db

from mongo console :
# a few usefull command on mongo cli
show dbs
use sharypic_development

# adding sparse index
db.users.dropIndex("invite_code_1")
db.users.ensureIndex({invide_code: 1}, {sparse: true, unique: true})

# rename a datbase
use 'sharypic-staging'
db.copyDatabase("sharypic-staging", "sharypic_development", this)
db.getCollecitonNames()

# querying object id
{_id: ObjectId('blah')} 

# removing stuffs
db.pictures.remove({ $and: [ {"event_id": ObjectId('4e11adb84fcd230001000044')}, {"_type": {$ne: "TwitterSource"}}] })

# restore a db
mongorestore -vvv sharypic_development