How are managed the sequences by JPA and Hibernate?

Posted by romaintaz on Stack Overflow See other posts from Stack Overflow or by romaintaz
Published on 2009-01-21T08:50:53Z Indexed on 2010/05/28 18:02 UTC
Read the original article Hit count: 196

Filed under:

hibernate

|

jpa

|

sequences

Hi all,

I am using Hibernate in my project, and many of my entities use a sequence for their technical keys. For example:

@Entity
@Table(name = "T_MYENTITY")
@SequenceGenerator(name = "S_MYENTITY", sequenceName = "S_MYENTITY")
public class MyEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_MYENTITY")
    @Column(name = "MY_ENTITY_ID")
    private Long entityId;

    ...

}

I have two questions about the ID generated by Hibernate when a new object of this class is persisted:

Why SequenceGenerator (from javax.persistence) has a default value of allocationSize set to 50 instead of 1? What are the interests of that?
What is the default algorithm used by Hibernate to calculate the generated ID? It seems that Hibernate uses the value returned by the sequence hosted by my Oracle database, but then modify it before assigning it to my entity...

© Stack Overflow or respective owner

Related posts about hibernate

Hibernate unable to instantiate default tuplizer - cannot find getter

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to use Hibernate to persist a class that looks like this: public class Item implements Serializable, Comparable<Item> { // Item id private Integer id; // Description of item in inventory private String description; // Number of items described by this inventory item private int… >>> More
Hibernate + PostgreSQL : relation does not exist - SQL Error: 0, SQLState: 42P01

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello, I am having some problems trying to work with PostgreSQL and Hibernate, more specifically, the issue mentioned in the title. I've been searching the net for a few hours now but none of the found solutions worked for me. I am using Eclipse Java EE IDE for Web Developers. Build id: 20090920-1017… >>> More
Problem connecting to Hsqldb via Hibernate when running a Eclipse GWT project.

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I'm trying to run a simple GWT project where I'm trying to do a simple persitence via hibernate to a HSQLDB database. The database I'm using I have been using for at least 2 years with several osgi applications without any problems. So all I done is reused the same configuration and added a simple… >>> More
Hibernate : load and

as seen on Stack Overflow - Search for 'Stack Overflow'
According to the tutorial : http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=27hibernateloadvshibernateget, If you initialize a JavaBean instance with a load method call, you can only access the properties of that JavaBean, for the first time, within the transactional context in which it… >>> More
Hibernate Exception, what wrong ? [[Exception in thread "main" org.hibernate.InvalidMappingException

as seen on Stack Overflow - Search for 'Stack Overflow'
I use netbean 6.7.1 to write "hello world" witch hibernate, but I get some errors, plz help me, thank you very much. my exception init: deps-module-jar: deps-ear-jar: deps-jar: Copying 1 file to F:\Documents and Settings\My Dropbox\DropboxNetBeanProjects\loginspring\build\web\WEB-INF\classes compile-single: run-main: Oct… >>> More

Related posts about jpa

Detach an entity from a JPA persistence context (JPA 2.0 / Hibernate / EJB 3 / J2EE 6)

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I wrote a stateless EJB method allowing to get an entity in "read-only" mode. The way to do this is to get the entity with the EntityManager then detach it (using the JPA 2.0 EntityManager). My code is the following: @PersistenceContext private EntityManager entityManager; public T getEntity(int… >>> More
AndroMDA maven code generation and JPA Annotations

as seen on Stack Overflow - Search for 'Stack Overflow'
I am using the AndroMDA plugin for maven to generate code from an uml diagram made in MagicDraw. When the code is generated, AndroMDA desings the JPA annotation for the persitence layer. I think that at the compilation process AndroMDA uses Naming Strategies to determine the Table and Column names… >>> More
How to populate Java (web) application with initial data using Spring/JPA/Hibernate

as seen on Stack Overflow - Search for 'Stack Overflow'
I want to setup my database with initial data programmatically. I want to populate my database for development runs, not for testing runs (it's easy). The product is built on top of Spring and JPA/Hibernate. Developer checks out the project Developer runs command/script to setup database with initial… >>> More
Eclipselink problem in a javase project

as seen on Stack Overflow - Search for 'Stack Overflow'
I am getting this error when I am running my eclipselink project. [EL Warning]: 2008.12.05 11:47:08.056--java.lang.NoClassDefFoundError: org/jboss/resource/adapter/jdbc/ValidConnectionChecker was thrown on attempt of PersistenceLoadProcessor to load class com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker… >>> More
JPA thinks I'm deleting a detached object

as seen on Stack Overflow - Search for 'Stack Overflow'
So, I've got a DAO that I used to load and save my domain objects using JPA. I finally managed to get the transaction stuff working (with a bunch of help from the folks here...), now I've got another issue. In my test case, I call my DAO to load a domain object with a given id, check that it got… >>> More