In "Hibernate in Action" I read about the best practice to implement hashcode and equals for the persistent objects.

It is not a good practice to use the "surrogate key" (database identifier property) because Hibernate doesn’t assign identifier values until an entity is saved.

Also it is not a good practice to include all persistent properties of the persistent class because instances from different sessions are no longer equal if one property is modified.

So the solution is to use a "business key" (natural key you’d use if you weren’t using a surrogate key). A business key is never null, it’s
unique, and it changes rarely (if ever).

My question arrises for generated Middlegen code which is something like the following :

public boolean equals(Object other) {
if ( !(other instanceof MyObject) ) return false;
MyObject castOther = (MyObject) other;
return new EqualsBuilder()
.append(this.getId(), castOther.getId())
.isEquals();
}

where "id" is the <id ... > in hibernate xml file.

So I suppose that we cannot rely on equals and hashCode methods generated by Middlegen and we must implement them using the business key. Is that true?

Thanks,
Mike

There is an extensive discussion of the equals/hashCode issue at http://www.hibernate.org/109.html