dropDups true not working mongodb

Question

I am using mongoDB shell with version 3.0.2 I am trying to ensure uniqueness constraint over a username field in collection users.

This is what I gave:

db.users.ensureIndex({"username": 1},{unique: true})

It gave me following error:

{
    "createdCollectionAutomatically" : false,
    "numIndexesBefore" : 1,
    "errmsg" : "exception: E11000 duplicate key error index: mybackend.users.$username_1 dup key: { : \"rahat\" }",
    "code" : 11000,
    "ok" : 0
}

Then i used, dropDups: true in the command:

 db.users.ensureIndex({"username": 1},{unique: true, dropDups: true})

Then too I get the same error:

 {
    "createdCollectionAutomatically" : false,
    "numIndexesBefore" : 1,
    "errmsg" : "exception: E11000 duplicate key error index: mybackend.users.$username_1 dup key: { : \"rahat\" }",
    "code" : 11000,
    "ok" : 0
}

I also saw this SO link but here it already had one index. Mine does not have one.

db.users.getIndexes() ->

[
    {
        "v" : 1,
        "key" : {
            "_id" : 1
        },
        "name" : "_id_",
        "ns" : "mybackend.users"
    }
]

I looked for this issue on github and restarted the mongo but to no use. What am I doing wrong? I think I am doing a silly mistake. Please help.

Answer 1

The drop duplicates functionality on index creation is no longer supported since Mongo version 3.0. See the compatibility changes page for the 3.0 release.