I want to create a unique user name for my users, but this will be not system generated. Users can choose his/her user name.

DB

MongoDB

Ex

Github user name

Current process

1. sign-up
2. get a verification link on the email
3. go to the link, like example.com/verify?token=xyz...

On verify page user can enter a user name, that user name must be unique across the DB.I don't want to keep duplicate user names.

Many websites have implemented this feature, like Github, GitLab, etc. But, I have explored some web about implementing this feature and I didn't get the desired result.

4. After entering the user name in step 3, the browser will make a POST request to the server.

5. Server will then check the DB that if this user name already exists or not, if this already exists then throw an error or process the user name otherwise.

This is working on my local PC, but I am not sure whether this will work when multiple users make a request with the same username within a time interval. Then, in this case, there may be some duplicates in DB.

case

There are two users A and B wants to create their user name on the system at the same time.

both are requesting the same user name

1. A: make the request for the user name u1
2. Server: check for A's user name is present or not in DB
3. B: make the request for user name u1
4. Server: A's user name is not present, save u1 as A's user name
5. Server: B's user name is not present, save u1 as B's user name

You can see, in the end, both users's haveing the same user name.

Is there any way to avoid this??

CodePudding user response：

The solution depends on your Database. If you are using SQL database, you can just add UNIQUE constrain to the field, so the database will enforce the uniqueness of an attribute value in the table. The first row will be inserted while another row will fail to insert with an error that the field is not unique.

Speaking of MongoDB, you also have a unique index.

CodePudding user response：

-> As the above answer suggested have a unique constraint on DB for user name and if the insert didn't happen send an error response stating username already taken also -> We do not need to wait until the user submits the request, as the user types in the user name, call an API to check if the username already exists, and while calling this cancel the previous request which we haven't got a response back. For example when the user types vi you send a request and it is still in progress but the user has typed vig now before sending the new request with 'vig' data, cancel the previous request. ( Ans simultaneously show the status whether taken or not as you get the responses )

• This improves the user experience. -> The cancelling of the requests can be done using cancel tokens in Axios, if you are going with Axios.

For MongoDB: If you can create an additional unique index based on a combination of fields, can't you use an additional dummy field ( which has the same data for all users), so now your username would stay unique? (I haven't used MongoDB a lot to be sure of this. )

OR this is mentioned in the Mongo DB documentation , create a proxy collection to maintain this username as a unique key, following the first segment in the below document https://docs.mongodb.com/manual/tutorial/unique-constraints-on-arbitrary-fields/