There are, generally speaking, 2 ways to refer to an entity's identifier property:

References to composite identifier properties follow the same naming rules. If the entity has a non-identifier property named id, the composite identifier property can only be referenced by its defined named; otherwise, the special id property can be used to rerference the identifier property.

Note: this has changed significantly starting in version 3.2.2. In previous versions, id always referred to the identifier property no matter what its actual name. A ramification of that decision was that non-identifier properties named id could never be referenced in Hibernate queries.