I've built out most of the functionality, now I'm getting stuck...
I am creating a private, web application that has an invite only registration system. An admin user sends an email invitation to a user, the user clicks the link, and takes them to a page where they can create an account that has been linked to their email address.
When the form is submitted and does not have any validation errors, the data is inserted into the database for the first time. The email column of the invitations table is unique, so this is the token that the user needs in order to verify that they have permission to create an account.
The situation that I am confused about is when the admin user tries sending an invitation to the same email address. The email address column is unique so there is an SQL error. I don't know if I should do a check for that email address before inserting that record in the database, or what I should do.
I want to create a re-send invitation feature for emails that get lost, or accidentally deleted. Which is why I didn't want the admin user to be able to send a duplicate email to the same person, rather, they should use the re-send feature.
I hope this is all making sense. Any insights would be appreciated.