Object equality in context of hibernate / webapp

Question

How do you handle object equality for java objects managed by hibernate? In the \'hibernate in action\' book they say that one should favor business keys over surrogate keys

Answer 1

I use to do it that way: equal and hashcode use the key when it has been set, otherwise equals uses the base implementation (aka ==). It should work too if hashcode() returns super.hashcode() instead of 0.

@Override
public int hashCode() {
    if (code == null) {
        return 0;
    } else {
        return code.hashCode();
    }
}

@Override
public boolean equals(Object obj) {
    if (obj instanceof PersistentObject && Hibernate.getClass(obj).equals(Hibernate.getClass(this))) {
        PersistentObject po = (PersistentObject) obj;

        if (code == null) {
            return po.code == null && this == po;
        } else {
            return code.equals(po.getCode());
        }
    } else {
        return super.equals(obj);
    }
}