,994 INFO Test Persist Save Merge:237 - Save entity ,002 DEBUG SQL:92 - select nextval ('hibernate_sequence') ,042 INFO Test Persist Save Merge:240 - Commit transaction ,096 DEBUG SQL:92 - insert into Author (first Name, last Name, version, id) values (? It delays the execution of the SQL INSERT statement for the new entity until it flushes the persistence context. But almost all of these differences disappear when you take a look at the internal implementation.,368 INFO Test Persist Save Merge:237 - Save entity ,482 DEBUG SQL:92 - select tbl.next_val from hibernate_sequences tbl where tbl.sequence_name=? ,584 INFO Test Persist Save Merge:240 - Commit transaction ,655 DEBUG SQL:92 - insert into Author (first Name, last Name, version, id) values (? The only ones that remain are 2 corner cases in which Hibernate might delay the retrieval of the primary key, the return type of the method and the support by other JPA implementations.
You will find persistence with JPA easier to understand if you think about object state management, not managing of SQL statements.
If you don't know the identifier values of the objects you are looking for, you need a query.
to a natural identifier, Hibernate only performs an SQL INSERT statement when it flushes the persistence context. Hibernate then delays the INSERT statement until it flushes the persistence context. ) You shouldn’t use the TABLE strategy because it requires row level locks on the primary key table and doesn’t scale well.
,979 INFO Test Persist Save Merge:237 - Save entity ,052 INFO Test Persist Save Merge:240 - Commit transaction ,123 DEBUG SQL:92 - insert into Author (first Name, last Name, version, id) values (? In this example, the flush happens when the transaction gets committed. If you use this strategy anyways, Hibernate performs an SQL SELECT statement to retrieve the next primary key value from the database and writes the new value to the database table. ) method behave differently because there are a few differences between the JPA specification and the Javadoc of Hibernate’s proprietary methods.
to store the changes of a detached entity in the database.
That’s why a lot of developers are wondering which of these methods they should use.In almost all situations, Hibernate generates the primary key value immediately and triggers an SQL statement if necessary, when you call the method.Which and when it does that depends on your primary key generation strategy: If you set the primary key value programmatically, e.g. ) And if you use the SEQUENCE, Hibernate performs an SQL SELECT statement to retrieve the next value from the database sequence.JPA’s merge method copies the state of a detached entity to a managed instance of the same entity.Hibernate, therefore, executes an SQL SELECT statement to retrieve a managed entity from the database.The missing dirty check causes an unnecessary SQL UPDATE statement when the entity and the corresponding database record contain the same values. ,191 INFO Test Persist Save Merge:335 - Before commit ,193 DEBUG SQL:92 - update Author set first Name=?