How to make user create on system only once ?

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I m facing a problem, I have API that sends a request with a list of email addresses, now what system does it check each email address from the database, if it exists then it ok we use userid else we create a new user.

The problem arises when we send multiple requests with the same list of email addresses then it throws an exception.because I have set a unique constraint on email column in DB.

What I have tried:

I think I have to create a singleton DB context and this context only create a user and return to the caller function.

Posted 25-Nov-17 8:00am

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Dave Kreskowiak 25-Nov-17 14:35pm

Your question makes little sense.

Are you asking how to check to see if an email address is in your user database first before trying to add it?

If you attempt to add the email address now, you're getting an exception because the email address already exists? Then handle the exception and return the user back to the page to pick a new email address and include an error message in the page that says that address is already in use.

Code Atom 26-Nov-17 0:10am

the use case is, first check if the user exists in DB or not, if not then create a new one else use existing one, now two threads parallelly try to create a user in their own thread scope and they try to commit their changes it basically throws an exception.

Dave Kreskowiak 26-Nov-17 0:21am

And the exception is?

Code Atom 26-Nov-17 0:24am

Transaction abort exception

Code Atom 26-Nov-17 0:26am

Am I need to add row version in user table for concurrency? and I am using serializable isolation in the transaction.

Dave Kreskowiak 26-Nov-17 9:40am

Are both threads trying to create the same email address?

Code Atom 26-Nov-17 11:54am

yes

Dave Kreskowiak 26-Nov-17 12:45pm

OK, so I already told you what to do. Handle the exception and tell the client that that email address has already been used.

You DO know what a try/catch block is for, right?

Code Atom 27-Nov-17 12:27pm

I have API when calling this API parallelly, it creates a user with an email address multiple times.

Dave Kreskowiak 27-Nov-17 15:13pm

Without seeing your API code, it's impossible to tell you what you did wrong.

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