We have a legacy db where all dates are stored as integers and nulls represented by zeros. We have user types that models the integer in database as Joda time, and it can handle translation of nulls into zero through the user type. However, for queries, I'm not sure what we'd have to do to translate the "is null" into "=0" when it goes from HQL to SQL. Is there a way to specify this behavior either in the user type, or the dialect class or elsewhere?

So this is what I ended up doing in the user type:

define a
public static final DateTime ZERO_DATE_TIME = new DateTime(0);

and translate that as zero when converting to database:

public void nullSafeSet(PreparedStatement st, Object value, int index, SessionImplementor session)
throws HibernateException, SQLException {
if (value == null || value == ZERO_DATE_TIME) {
st.setInt(index, 0);
} else {
doInstanceCheck(value);
DateTime cal = (DateTime) value;
st.setInt(index, getDate(cal));
}
}

So in the query is just set to this special date and it seems to work.

Well. It was awesome the way you solved it.