I am new to JPA
I want to insert a record into the database (Insert and not Update).
But when I use repository.save() method, then it acts as an Update query if the record is already present.
How to do only insert in this case(throw an exception if record already exists)?
How spring data JPA decides to call entityManager.persist(…) or entityManager.merge(…) method
You could use the exists() method of the repository and call save() only if the record does not exist.
Related
I have a question about methods deleteById and delete in spring-data.
what is the difference between these methods? When should I use delete/deleteById?
I search google for one day but i have no answer for it
The method deleteById will throw an EmptyResultDataAccessException if the supplied id does not exist, whereas the method delete will silently return if the supplied entity hasn't been persisted yet, or for whatever reason it cannot be found by the EntityManager.
Also, as #manish noted in their comment, the method deleteById actually calls the delete method internally if the findById method is able to find an entity.
As of Spring-Boot 3.x and it's respective version of spring-data-jpa,
the method deleteById will no longer throw the Runtime exception of EmptyResultDataAccessException in case the provided id did not existed in database to be deleted.
So the only difference from now on between deleteById(Id id) and delete(T entity) is that the first one will take as parameter the id and try to locate the respecting entity in database with that id to be deleted, while the second one will take as parameter directly the entity to be deleted.
I am trying to implement transaction management in EJB application with Openjpa as ORM tool.
I am trying to implement a scenario where if a db update operation fails for an entity, then db operations for all other entities in same transaction
also rollback. So I have an entity A and I explicitly set one of it's non-nullable field to null and call entitymanager.merge() method for this entity.I expect that due to non-nullable constraint db operation would fail and PersistenceException would be thrown. But nothing of that sort happens, though A's state is also not persisted.
But if I first call find() using A's id and then call merge(), I get exception.
I used to think that merge() alone is sufficient to take care of all. Why do I need to explicitly call find() before merge?
Changes are not required to be synchronized to the database until you call em.flush(), or commit the associated transaction.
How does jpa entity call back method work?
are they only notified when doing single jpa operations like em.merge() and em.create() ? or they will be notified if i use em.createQuery().executeUpdate()? (also for namedQueries)
Can i use them instead of real database triggers?
I did not find a direct statement, but from the quote below (JPA 2.1 spec,
Chapter 4.10 Bulk Update and Delete Operations), I understand that in a BULK update or delete, the listeners are not called, because the persistence context won't see the changed entities:
[In a bulk update or bulk delete] The persistence context is not synchronized with the result of the
bulk update or delete.
So the answer is: only in single JPA operations will the listeners be changed.
A listener is not the same as a database trigger: a constraint of JPA listeners is that you should not change relationships or other entities inside them (although some JPA providers may support this).
I am attempting to update an existing record using JPA. The following link seems to suggest that the only way to update a record would be to write the update query for it
enter link description here
Which is fine. But again, I am wondering why am I pulling this out of stored proc to use all f the magic of open JPA?
I thought that If I had an instance of a JPA object that if I tried to persist to the database using a call similar to this
emf.persist(launchRet)
the JPA framework would check to see if the record allready exists, if so, it would then proceed to make the changes to that record, if not, it would just add a new record. Which would be really cool. Instead, I am going to have to end up writing all that logic myself in an update query. Which is fine, But why can't I just use a stored proc and just pass it all the necessary values?
UPDATE: CODE EXPLAINING WHAT MY LAST COMMENT IS ALL ABOUT
try{
launchRet = emf.find(QuickLaunch.class, launch.getQuickLaunchId());
if(launchRet==null){
emf.getTransaction().begin();
emf.persist(launchRet);
emf.getTransaction().commit();
}
else{
emf.refresh(launchRet);
}
}
The variable launch is passed into the method...
public QuickLaunch UpdateQuickLaunchComponent(QuickLaunch launch)
Would I simple just set the found launch launchRet equal to the launch that was passed in?
Read the link that you posted:
You can modify an entity instance in one the following ways:
Using an Updating Query
Using the Entity's Public API
[...]
The way used in 99% of the cases is the second way:
Foo someExistingFoo = em.find(Foo.class, someExistingFooId);
someExistingFoo.setSomeValue(theNewValue);
// no need to call any persist method: the EM will flush the new state
// of the entity to the database when needed
Of course, the entity can also be loaded via a query, or by navigating through the graph of entities.
If you have a detached entity, and you want to persist its state to the database, use the EntityManager.merge() method. It finds the entity with the same ID as the detached one passed as argument, copies the state from the detached entity to the attached one, and returns the attached one:
Foo attachedModifiedFoo = em.merge(detachedFoo);
If the detached entity isn't persistent (i.e. doesn't have any ID), then it is created and made persistent.
I use EntityManager to save/update my entities in database and Hibernate as jpa provider. My transactions are handled by container.
The problem: I need to add an entity that might have been already stored in database, so an exception will be thrown. In this case I need to repeat insertion but with another value. But as long as an exception is thrown the session has gone bad and I need to create a new session and rollback the transaction. How can I do this when I'm using CMT? Or if there is another way to do this?
Thank you.
You could use the TransactionAttribute(REQUIRES_NEW) for your persistence method. If the bean invoking your method will catch an exception, it might do some changes and invoke the method once again.
This will rollback just the persistence-method transaction - not the invoking bean one.
However, remember that if your Use Case doesn't require you to do EntityManager#persistence(-), you might be interested in EntityManager#merge(-) operation. It will persist the entity if it doesn't already exist or update it if it already exists (the existence is checked based on the PK).
HTH.
You might want to use EntityManager#find(Class, PK) to check for an already persisted entity. A null result means there's no such entity ( ----> persist(.) ), otherwise you update with the merge(.) method.