hibernate unique key validation

Question

I have a field, say, user_name, that should be unique in a table.

What is the best way for validating it using Spring/Hibernate validation?

Answer 1

I think it is not wise to use Hibernate Validator (JSR 303) for this purpose. Or better it is not the goal of Hibernate Validator.

The JSR 303 is about bean validation. This means to check if a field is set correct. But what you want is in a much wider scope than a single bean. It is somehow in a global scope (regarding all Beans of this type). -- I think you should let the database handle this problem. Set a unique constraint to the column in your database (for example by annotate the field with @Column(unique=true)) and the database will make sure that the field is unique.

Anyway, if you really want to use JSR303 for this, than you need to create your own Annotation and own Validator. The Validator have to access the Database and check if there is no other entity with the specified value. - But I believe there would be some problems to access the database from the Validator in the right session.