Use a own class for interaction with database. DONT do this in the entity itself!
Solution1:
You can use @Version
for current object. https://weblogs.java.net/blog/2009/07/30/jpa-20-concurrency-and-locking . You get a Exception when its not the newest version and you tried to merge it.
Solution2:
You can use find(...)
http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#find%28java.lang.Class,%20java.lang.Object%29
With class and ID from the current Item to load the actual state from DB (or Persistence Context if already exists in it).