There are reports that messages of this sort were due to bugs in one or more Hibernate releases. But this is also a legitimate error.
I wasted a lot of time before it hit me. The original code was:
@SuppressWarnings("unchecked")
public List<State> getStatesForCountry(String countryID) {
final String SQLCOMMAND =
"SELECT c " + "FROM "
+ State.class.getSimpleName() + " c "
+ " WHERE c.parentCountry = :countryID"
+ " ORDER BY c.StateName ASC";
Query query = entityManager.createQuery(SQLCOMMAND);
query.setParameter("countryID", countryID);
List<State> results = query.getResultList();
return results;
}
It should have been:
@SuppressWarnings("unchecked")
public List<State> getStatesForCountry(String countryID) {
final String SQLCOMMAND =
"SELECT c " + "FROM "
+ State.class.getSimpleName() + " c "
+ " WHERE c.parentCountry = :country"
+ " ORDER BY c.StateName ASC";
Query query = entityManager.createQuery(SQLCOMMAND);
Country country = findCountry(countryID);
query.setParameter("country", country);
List<State> results = query.getResultList();
return results;
}
Where findCountry is simply an entityManager.find(Country.class, countryID);
This is a sneaky one because when the database is laid out, you think in terms of foreign keys. But in ORM, you don’t see those keys directly – they translate to object references. So the original version was attempting to compare an object to the key of the object instead of an instance of the object.
I can only plead distraction. The object model in question had been designed by someone else. Instead of accessor methods, it was using direct field access (which I avoid for a number of reasons). Further aggravating the issue was that the fields were all given names starting with an upper-case letter as though they were independent classes instead of properties.
But even without distractions, it’s not too hard to make this mistake.
