Add unique index while also remove the documents which has duplicated key index

add_unique_remove_duplicates.js

// Let's say there is a fruits collection where it contains documents as follow
db.fruits.insert({'name':'pear'})
db.fruits.insert({'name':'apple'})
db.fruits.insert({'name':'pear'})

// Then, we want to prevent another document with name = pear can be inserted into fruits collection
// In the other words, we want to make the name property become unique.
// And also, duplicated document would be removed

db.fruits.ensureIndex({'name':1}, {'unique':true, 'dropDups':true})