Hi,
i have written one sample application ,and i used MySql database.

when i used the below code ,the data what ever i have given is stored into the table.
Transaction tx = session.beginTransaction();
tx.begin();
Book book=new Book();
book.setId(5);
book.setBookName("abc");
session.save(book);
tx.commit();

but if i use session.saveOrUpdate(book); instead of session.save(book);
previous data is deleting and current data only storing into the table.

and one more thing if i want retrive the data from table
i used below code for that

Criteria criteria = session.createCriteria(Book.class);
System.out.println(criteria.list());


in output ,it is showing as

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select this_.id as id0_0_, this_.bookName as bookName0_0_ from book this_
[]


it is showing empty in the criteria.list(),

any one help me , i am not getting the problem is from code or MySql .