当MongoDB上的唯一索引失败时生成替代方案

Question

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:

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

Answer 1

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 } 

2. 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.