[FLOW3-general] Validate if an object is unique

[Widmer Cornel]

In my application it is possible to create new users. The e-mail adress is used as identifier for the username (account). When I create a new user over the form with an existing e-mail flow throws the error: "Integrity constraint violation: 1062 Duplicate entry".

How can I validate this?

I tried to validate on the controller-action with "UniqueEntity" but then i got the error: "The object supplied for the UniqueEntityValidator must have at least one identity property."

Is there a way on the model to achive this?