Generate Alternative when Unique Index fails on MongoDB

Question

Generate Alternative when Unique Index fails on MongoDB

So when users sign up via Google, Twitter or such, names can overlap. Within my app, usernames have a unique index. Since a new document is put into the collection whenever someone signs in for the first time, sometimes the unique index fails. The code for signing up a user goes like this:

module.exports.findOrCreateUser = (provider, id, data, done) ->
    User.findByAuth provider, id, (err, user) ->
        if err? then done err
        else if user? then done null, user
        else
            user = new User
                auth: [{id: id, provider: provider}]
                name: data.name
                email: data.email
            user.save (err) ->
                if err? then done err else done null, user

So I have two problems here:

How can I check if err is a unique index error?
What is the most efficient way to append an unique suffix to the user's name?

node.js
mongodb
oauth
coffeescript

Answer 1

The err object has a message attribute that matches the error message the mongo shell would give. Checking if there's a unique index error should look something like this:
```
if (err && err.message.indexOf('E11000 ') !== -1) {
    // this _id was already inserted in the database
}
```
I agree with @innoSPG to append the service name to username. If you don't want indication of the service associated with the username just append a counter to the username and increment it every time it's used.