Saving/updating object with hibernate

Question

My class Foo has method:

 protected void saveMany(Collection<T> many) {  
    for(Object one : many) {
            one = session.merge(one); // also tried this commented out
            session.saveOrUpdate(one); // session.merge(one);   
        }

Tried to use saveOrUpdate and also merge, but both gave me this exception:

Error: Invocation of method 'saveMany' in class Foo threw exception class org.hibernate.HibernateException : org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [Bar#581301]

How to fix this?

Side note:

When I truncate my table, the saving part works, but when I have the table populated, and run this method again, thus updating the table, it fails, with this exception

Answer 1

If you have a detached instance of a Class with @Id that already exists in the Hibernate Session cache, then you will have to call merge() to merge the detached instance into the cache. Then you should call saveOrUpdate() .

But you have to be careful to persist the instance returned from the call to merge() and not the instance you passed in as a parameter. So you code has to look like this

mergedOne = session.merge(one);
session.saveOrUpdate(mergedOne);

If you're operating inside a transaction the database will not be updated until the session ends and the transaction commits, or you explicitly call flush()

Answer 2

It says that you are trying to save a new object with an Id already used by another one.

Probably, you do not have properly implemented equals and hashCode . So, hibernate finds that you want to save Object2 with id1, and in the database there is Object2 with id1, but not Object2.equals(Object1)

Answer 3

You have multiple versions of "one" in the cache of your Hibernatesessions!

You must must find the instances of "one" and remove the cache-information from the Hibernatesessions using ".evict(...)".

Finally you can call saveOrUpdate succesuflly!

Answer 4

You are probably trying to Save List<T> which has one or more equals objects.

Use SaveOrUpdate or merge to solve it or simpply try to make all objects unique.