I have an existing database of a film rental system. Each film has a has a rating attribute. In SQL they used a constraint to limit the allowed values of this attribute.
The problem is, I think, that JPA was never incepted with the idea in mind that we could have a complex preexisting Schema already in place.
I think there are two main shortcomings resulting from this, specific to Enum:
Help my cause and vote on JPA_SPEC-47