I am still a beginner in hibernate.I have started reading the user guide in which i found this architecture.
I know that hibernate is a jpa implementation and the jpa jar contains only interfaces.But i want to understand why JPA API is in the same level as Hibernate native api.
And if JPA contains only Interfaces how can we call for example entityManger.persist(entity) and normaly the entity manager is an interface.
where is the entity manger implementation ???
I know that hibernate is a jpa implementation and the jpa jar contains only interfaces.But i want to understand why JPA API is in the same level as Hibernate native api.
Because you can either use the JPA API (EntityManager, EntityManagerFactory etc) or Hibernate native API (Session, SessionFactory etc) to interact with the ORM entities and the database.
And if JPA contains only Interfaces how can we call for example entityManger.persist(entity) and normaly the entity manager is an interface. where is the entity manger implementation ???
JPA API like EntityManager, EntityManagerFactory etc are implemented by Hibernate (one of the JPA implementations, other like EclipseLink etc do exist). You will find that implementation in one of the hibernate jar files. .
A quick ref of Hibernate implementation of EntityManagerFactory here on grepcode
Related
I have a service with spring data jpa which uses multiple datasource. One of the datasource is used as the main storage and Entity is used there and repositories are described. Other datasources are used simply to call stored procedures and functions.
Can you please tell me if I can somehow create a spring data jpa repository for datasource without an entity and use the #Procedure annotations to force the function to call the stored procedure I need?
I read about https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.custom-implementations and just wrote my repository implementation. Looking for alternative, more convenient use cases for the spring data jpa api.
You need to use some entity as JPA is domain driven, refer Any way to use the `#Procedure` annotation without an entity?
and
Using Spring #Procedure to call StoredProcedure without binding to a table
In my opinion, you should use Just use JDBC template.
The problem is how to implement tracking of data changes on e.g. master detail tables i.e. two entities in one to many relationship in Spring Boot/Spring Data.
After storing data, to be able to get the master entity with its details at specific version, and to have functionality to revert it to specific version.
You can use Hibernate Envers to audit and version your persistence entities changes.
The Envers project aims to enable easy auditing of persistent
classes. All that you have to do is annotate your persistent class or
some of its properties, that you want to audit, with #Audited. For
each audited entity, a table will be created, which will hold the
history of changes made to the entity. You can then retrieve and query
historical data without much effort.
Similarly to Subversion, the library has a concept of revisions.
Basically, one transaction is one revision (unless the transaction
didn't modify any audited entities). As the revisions are global,
having a revision number, you can query for various entities at that
revision, retrieving a (partial) view of the database at that
revision. You can find a revision number having a date, and the other
way round, you can get the date at which a revision was commited.
The library works with Hibernate and requires Hibernate Annotations or
Entity Manager. For the auditing to work properly, the entities must
have immutable unique identifiers (primary keys). You can use Envers
wherever Hibernate works: standalone, inside JBoss AS, with JBoss Seam
or Spring. source
You can query for historic data in a way similar to querying data via
the Hibernate criteria API. The audit history of an entity can be
accessed using the AuditReader interface, which can be obtained with
an open EntityManager or Session via the AuditReaderFactory. source
With Hibernate Envers you can record your data changes and then access it whether using your persistence context or SQL in order to apply your version changes using the provide revision id. With it you've the 80% of the task done.
Check this tutorials
Setting up Hibernate Envers with Spring Boot
Auditing with JPA, Hibernate, and Spring Data JPA
Hibernate Envers: Simple Implementations
If you use JPA, object auditing frameworks like hibernate envers or javers might help
I know that Spring Data JPA uses Hibernate, however, I have some questions that need clarification.
Will I be able to use other Hibernate features such as C3P0, Hibernate second level caching, or Hibernate sessions if I use Spring Data JPA?
What are the advantages of using #Query for writing custom queries over using hibernate sessions and HQL?
Is there any performance difference between using Spring Data JpaRepository query methods and using Hibernate HQL?
I have seen the other similar questions here and they don't answer these questions.
I know that Spring Data JPA uses Hibernate
No. It uses JPA. Even though Hibernate is the default JPA implementation of Spring Boot, and the most popular JPA implementation, any JPA engine can be used.
Will I be able to use other Hibernate features such as C3P0
C3P0 has nothing to do with Hibernate. It's a connection pool. You can use any connection pool you wnt both with Spring and with Hibernate. Spring Boot uses HikariCP by default, and I would stick to that (it's a very good pool).
Hibernate second level caching
Yes.
or Hibernate sessions if I use Spring Data JPA?
There's really no good reason to use the old, proprietary Hibernate Session API, instead of using the standard JPA API. If you really need to, I don't see why you couldn't use it, but I wouldn't (and never had to).
What are the advantages of using #Query for writing custom queries over using hibernate sessions and HQL?
Query takes a HQL (JPQL, to be exact) query. If you use Query, you use HQL. The advantage is that you just need to declare the query. the binding of parameters, execution of the query, paging, etc. are done for you by Spring. But you can use custom repository implementations and use the native JPA API if you need to.
Is there any performance difference between using Spring Data JpaRepository query methods and using Hibernate HQL?
No.
My application is using Spring 2.5, and native TopLink 10g. I want to migrate my application from native TopLink to EclipseLink.
Currently each DAO in my application extends TopLinkDaoSupport.java (in Spring 2.5), in order to use the #getSession() method for all DB operations, but the return type of the method is oracle.toplink.sessions.Session instead of org.eclipse.persistence.sessions.
Is there any solution of said problem?
I would also recommend to use JPA instead of the old TopLink API.
If you really need access to Session object, you can get it from EntityManager too. Check org.eclipse.persistence.internal.jpa.EntityManagerImpl in EclipseLink - this is a class that implements EntityManager. There is a getDelegate() method implemented that returns this (EntityManagerImpl) so ((org.eclipse.persistence.jpa.JpaEntityManager)[EntityManager].getDelegate()).getActiveSession() gives you org.eclipse.persistence.sessions.Session.
I'm using Hibernate Validator 4.0.2, Spring 3.0 and Hibernate 3.3.2 (which, as I understand it, is pre-JPA2) as a JPA 1 provider.
I've found it easy to integrate the Validator into the MVC layer (it just works) but can't see how to integrate the validator automatically into the JPA entityManager (JPA 1).
Basically, I have some entities that will be persisted but that do not come from the web layer and have therefore not already been validated. I'd like a neat way of running them through the validator pre-persist.
Is there an easy way of doing this? I'm aware that if I was using a JPA 2 provider (like Hibernate 3.5 when it is released), it'd be almost automatic. That's roughly what I'm looking for.
You need to write an entity listener and to trigger validation on #PrePersist, #PreUpdate and even #PreRemove (there are valid use-case for that). See Bean Validation with JPA 1.0 for a code sample.