Unique Index on a mongodb's collection

unique_index.js

// Let's say there is a fruits collection where it contains a pear document
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

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

// Let's push a new document that has different name than to the existing one
db.fruits.insert({'name':'apel'})

// Then push another new document whose name is same as an existing document's in the collection
db.fruits.insert({'name':'pear'})