When switching from Hibernate to JPA a lot of people are dismayed to find that method missing. And figuring out what piece of code persisted (or merged or retrieved) that other entity is harder than figuring out why we get a "detached entity passed to persist" message.
If the primary key already present in the table, it cannot be inserted.
based upon your requirement for persisting object into Database.
To understand the methods better it is good to understand the different states Hibernate managed entities go through.
The starting point for new entities is the transient state.
This is the central API class abstracting the notion of a persistence service.
The lifecycle of a Session is bounded by the beginning and end of a logical transaction. Those of you that have worked with plain Hibernate will probably have grown quite accustomed to using the method figures out whether the object is new or has already been saved before.In the first case the entity is saved, in the latter case it is updated.I can create the objects, but when I load one, change a property and call save Or Update I can't see any update ...How come save Or Update does not work for the save part but does work for the update?(Long transactions might span several database transactions.) The main function of the Session is to offer create, read and delete operations for instances of mapped entity classes.