Unique Key Validation

@UniqueConstraint Annotation does not validate the value of entity field. It will not catch the org.hibernate.exception.ConstraintViolationException.


Example:
@Table(name = "user", uniqueConstraints = @UniqueConstraint(columnNames = "username"))

Error:
ERROR [AbstractFlushingEventListener] Could not synchronize database state with session org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update...


SOLUTION: Custom Validator
----------------------------------------
To solve this problem, I created a custom validator to do the validation in JSF before persist the entity.
Seam provides annotations to allow us to use Seam components as JSF converters and validators.


@Name("usernameValidator")
@BypassInterceptors
@org.jboss.seam.annotations.faces.Validator
public class UsernameValidator implements javax.faces.validator.Validator {


public static final String VERIFICATION_MSG_EXPR = "#{messages['validator.duplicateError']}";

public void validate(FacesContext context, UIComponent cmp, Object value)throws ValidatorException
{

String ejbql = "select u from User u where u.username=:username";

String username = (String)value;

EntityManager em = (EntityManager) Component.getInstance("entityManager");
Query query = em.createQuery(ejbql);
query.setParameter("username", username);

List list = query.getResultList();

if (!list.isEmpty()) {

FacesMessage msg = new FacesMessage();
msg.setSummary(Interpolator.instance().interpolate(VERIFICATION_MSG_EXPR));
msg.setSeverity(FacesMessage.SEVERITY_WARN);
throw new ValidatorException(msg);
}
}
}



In JSF:

Registers the Seam component as a JSF validator. Below example is a validator which injects another Seam component. The injected component is used to validate the value.


<h:inputText id="username" value="#{userHome.instance.username}" validator="usernameValidator"/>