The issue is the following: in ma Karaf container, I have two modules, the first one is used to fetch data in the DB via a JPA interface implemented by Hibernate. Collections are fetched in a lazy way.
The second module gets the object containing the collections. When trying to access elements of a collection, an error is thrown:
failed to lazily initialize a collection of role:
mapp3.model.ProductDefinition, could not initialize proxy - no Session
It has no session to access the DB and fetch the missing elements.
I know in J2EE there is a concept of Sticky Session that makes a Thread create and share the same session across all beans.
It there something similar in Karaf/OSGi or is there another way of properly acheiving lazy loading between different modules ?
I have just implemented a similar feature in Aries JPA 2.1.0. It uses the OSGi Coordinator spec to share an EntityManager session on a thread. It works together with Aries transaction blueprint 1.3.0 which now also uses a Coordination. Both are available in Apache Karaf 4.0.1.
So to achieve a session that is kept over several calls between beans you annotate the outermost method involved with #Transactional. If you do not want an actual transaction but just the shared EM then you can use #Transaction with type Support. So starting from this method all calls made downwards will share the same em.
So for example you can do something like this:
#Transactional
public void myServiceMethod() {
Person person = personRepo.getPerson();
List<Task> person.getTask();
}
So in the example above the PersonRepo would inject the EntityManager using #PersistenceContext and work with it.
MyService.myServiceMethod would be on the service layer and should not know about jpa or the EntityManager. Still using the #Transactional annoation the method would provide a coordinaton over the execution of the method that holds the EntityManager.
Also see my example Apache Karaf Tutorial Part 9 - Annotation based blueprint and JPA. The example does not show the overarching #Transactional but should get you started easily if you want to dig into it. As soon as the upcoming Aries releases are done I will also create an example that shows exactly the case you are looking for.
Related
I have a Spring-boot project where I have a service bean with 2 #Transactional annotated methods.
These methods do read-only JPA (hibernated) actions to fetch data from an HSQL file database, using both JPA repositories and lazy loaded getters in entities.
I also have a cli bean that handles commands (Using PicoCLI). From one of these commands I try to call both #Transactional annotated methods, but I get the following error during execution of the second method:
org.hibernate.LazyInitializationException - could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:602)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:217)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:581)
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:148)
at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:188)
at java.util.Spliterators$IteratorSpliterator.estimateSize(Spliterators.java:1821)
at java.util.Spliterator.getExactSizeIfKnown(Spliterator.java:408)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
at <mypackage>.SomeImpl.getThings(SomeImpl.java:<linenr>)
...
If I mark the method that calls both #Transactional annotated methods with #Transactional itself, the code seems to work (due to there now only being 1 top level transaction I presume?).
I just want to find out why I cannot start multiple transactions in a single session or why the second transaction doesn't start a new session if there are none.
So my questions are:
Does this have to do with how hibernate starts a session, how transactions close sessions or anything related to the HSQL database?
Is adding an encompassing transaction the right way to fix the issue
or is this just fighting the symptom?
What would be the best way to be able to use multiple #Transactional annotated methods from one method?
EDIT: I want to make clear that I don't expose the entities outside of the transactional methods, so on the surface it looks to me like the 2 transactional methods should be working independently from one another.
EDIT2: for more clarification: the transactional methods need to be available in an api and the user of the api should be able to call multiple of these transactional methods, without needing to use transactional annotations and without getting the LazyInitializationException
Api:
public interface SomeApi {
List<String> getSomeList();
List<Something> getThings(String somethingGroupName);
}
Implementation:
public class SomeImpl implements SomeApi {
#Transactional
public List<String> getSomeList() {
return ...; //Do jpa stuff to get the list
}
#Transactional
public List<Something> getThings(String somethingGroupName) {
return ...; //Do other jpa stuff to get the result from the group name
}
}
Usage by 3rd party (who might not know what transactionality is):
public someMethod(String somethingGroupName) {
...
SomeApi someApi = ...; // Get an implementation of the api in some way
List<String> someList = someApi.someList();
if (someList.contains(somethingGroupName) {
System.out.println(someApi.getThings(somethingGroupName));
}
...
}
It seems that you are accessing some not initialized data from your entities after the transactions have ended. In that cases, the persistence provider may throw the lazyinitialization exception.
If you need to retrieve some information not eagerly loaded with the entities, you may use one of two strategies:
annotate the calling method also with #Transactional annotation, as you did: it does not start a new transaction for each call, but makes the opened transaction active until your calling method ends, avoiding the exception; or
make the called methods load eagerly the required fields USING the JOIN FETCH JPQL idiom.
Transaction boundaries requires some analysis of your scenario. Please, read this answer and search for better books or tutorials to master it. Probably only you will be able to define aptly your requirements.
I found that hibernate out of the box doesn't reopen a session and therefore doesn't enable lazy loading after the first transaction has ended, whether or not subsequent jpa statements are in a transaction or not. There is however a property in hibernate to enable this feature:
spring:
jpa:
properties:
hibernate.enable_lazy_load_no_trans: true
This will make sure that if there is no session, then a temp session will be created. I believe that it will also prevent a session from ending after a transaction, but I don't know this for sure.
Partial credit goes to the following answers from other StackOverflow questions:
http://stackoverflow.com/a/32046337/2877358
https://stackoverflow.com/a/11913404/2877358
WARNING: In hibernate 4.1.8 there is a bug that could lead to loss of data! Make sure that you are using 4.2.12, 4.3.5 or newer versions of hibernate. See: https://hibernate.atlassian.net/browse/HHH-7971.
So, I have an application running on WildFly10, which uses JSF, Spring (DI), JPA, Spring Data;
Right now we're trying to move it to CDI and remove Spring(DI). For now we'll keep Spring Data.
So, I set up CDI and made an EntityManager producer.
#Produces
#Dependent
#PersistenceContext
public EntityManager entityManager;
So, I'm able to inject repositories with CDI and all.
However on my original environment we had a custom repository factory,that was defined in my SpringConfiguration like this:
#EnableJpaRepositories(basePackages = {"com.foo.repository" }, repositoryFactoryBeanClass=CustomJpaRepositoryFactoryBean.class)
So, the question is, how can I define this repositoryFactoryBeanClass=CustomJpaRepositoryFactoryBean.class on a CDI environment?
The current implementation doesn't allow the configuration of the JpaRepositoryFactoryBean as one can see from the code where it gets instantiated.
So I guess you have the following options:
reimplement the instantiation process.
open a feature request.
do 2. and 1. in a reusable way and submit the result as a PR for the issue.
When trying to solve this problem I found that the custom impl was not being picked up. The solution suggested in this question helped me however: https://stackoverflow.com/a/38541669/188624
Basically is uses Java8 default interface method to provide the additional functionality. I had to use the "CDI.current().select" method to get hold of the entity manager though as property injection of course won't work.
I tested with Spring Data JPA 2.0.0
For personal education I am currently developing a little application framework around Guice to learn-by-doing how Spring etc. work behind the scenes.
Intro
Just for the sake of context, here is what I have so far and plan to do so you get a feeling for what I try to archive:
Context (Core)
ApplicationContext/-Configuration
Modules (auto discovered, setting up the Guice bindings)
Extensions
Config: #Config
Locale: #Locale and i18n services
Resources: #Property, #Resource and some classes providing easy access to resources
Persistence: Problems - there we go!
Question
I'd like to use the JDO standard (and its reference implementation DataNucleus) for the persistence layer. Setting up the PersistenceManagerFactory was easy, so was using it in a basic manner. I am however targeting a typical service / repository layer architecture, e.g.:
Person
PersonRepository (JDO)
PersonService (Transactions, using PersonRepository)
That alone wouldn't be too hard either, but as soon as I tried properly integrating transactions into the concept I got a bit lost.
Desired
class PersonService {
#Transactional(TxType.REQUIRED)
public Set<Person> doX() {
// multiple repository methods called here
}
}
class PersonRepository {
private PersistenceManagerFactory pmf;
public Set<Person> doX() {
try (PersistenceManager pm = pmf.getPersistenceManager()) {
pm.....
}
}
}
Difficulties
DataNucleus supports RESOURCE_LOCAL (pm.currentTransaction()) as well as JTA transactions and I would like to support both as well (the user should not have to distinguish between the two outside the configuration). He should not have to bother about transaction handling anyway, that is part of the annotation's method interceptor (I guess).
I'd love to support the #Transactional (from JTA) annotation that can be placed on service layer methods. Knowing that annotation is not per-se available in JDO, I thought it could be made usable as well.
How exactly should the repository layer "speak" JDO? Should each method get a PersistenceManager(Proxy)from the PersistenceManagerFactory and close it afterwards (as in the example) or get a PersistenceManager injected (rather than the factory)? Should each method close the PersistenceManager (in both scenarios)? That would not work with RESOURCE_LOCAL transactions I guess since a transaction is bound to one PersistenceManager.
What I tried
I have a JDOTransactionalInterceptor (working with pmf.getPersistenceManagerProxy) and a JTATransactionalInterceptor (very similar to https://github.com/HubSpot/guice-transactional/blob/master/src/main/java/com/hubspot/guice/transactional/impl/TransactionalInterceptor.java working with a ThreadLocal)
Summary
I am aware that my question may not be as clear as desired and mixes the service / repository layer questions (which is my main problem I think) and transaction stuff (which I could figure out once I understand how to properly use PMF/PM in repository layer I think)
There is no scope à la RequestScoped etc. I just want the first #Transactional method call to be the starting point for that whole thing (and that is the point: Is this impossible and the PMF/PM have to be scoped before and I have to direct my thinkings into that direction?)
Thanks for any clarification / help!
This is with reference to JPA 2.0: Adding entity classes to PersistenceUnit *from different jar* automatically and Unable to call Hibernate/QueryDSL from another maven subproject
It seems that Hibernate 4 had a great way to dynamically load entity classes using
org.hibernate.integrator.spi.Integrator service.
Now when using Hibernate 5, the Integrator interface's integrate method gives me
public void integrate(Metadata metadata, SessionFactoryImplementor sessionFactory,
SessionFactoryServiceRegistry serviceRegistry)
{
}
Where metadata is of type org.hibernate.boot.Metadata
I am unable to call addAnnotatedClass(), neither I am able to obtain the original Configuration object that was there in Hibernate 4.
How do I get around with this?
I am using maven and jetty.
I am not using spring (so please do not provide any spring based solution)
This was actually related to something I was wrestling with over the weekend in getting caught up on Hibernate 5. You can read about the planned changes related to the Configuration class in the latest Javadoc for Hibernate 4. The new place for getting info on all loaded entity classes including annotated entities is the Metadata class you mentioned. It has a getEntityBindings() method that will return the PersistentClass entity metadata representation for known all entities. This Collection is immutable however.
Recommendation is that you rethink using an Integrator to add entity bindings at runtime. This may have worked in the past, but the docs clearly point towards that not being intentional as this should be done at the time of initialization. The Metadata and SessionFactoryImplementor are for the most part immutable once built, and so the Integrator's intended purpose is not to modify these configuration items but instead use them as information on how to configure new Service integrations using the SessionFactoryServiceRegistry.
And if you're finding it annoying to configure your Session to find all your annotated classes at runtime, I suggest you try using the EntityManagerFactory approach for initializing Hibernate as it is far more straightforward and uses standard JPA syntax that can be switched to a handful of other providers if you ever need to. This will automatically scan for annotated entities on your behalf. The API is a bit more simplified and limited, but if you really ever need the power of native Hibernate-specific functionality there is a way to access the native underlying API.
I am using following code
TestDAO {
Session session = null;
public TestDAO() {
this.session = HibernateUtil.getSessionFactory().getCurrentSession();
}
//...more code create,update ...
//each method starts a transcation using "tx= session.beginTransaction();"
}
1)Now should i commit the transcation using tx.commit for a fetch operation too or only for save/update operation??
2)Should i create a seperate instance of TestDAO every time i need?Or should i create a singleton class that returns a single instance of DAO everytme?Will this have a problem?
You don't need tx.commit() for fetch operation. That is only needed for any save, update or delete. Close the session after data fetching.
If your application connect to only one database then use of single DAO is better. Spring framework encourages this. You will find more details about this on the following link
Don't repeat the DAO!
Transactions should not be the responsibility of the DAO, those really need to be controlled at a higher level. A DAO should be something that does queries and updates without being aware of the bigger picture, calls to DAOs can be grouped within an object like a Spring service or EJB session bean which is responsible for deciding what needs to go together in a transaction. This makes your DAO code more reusable since it doesn't have to know as much about the context in which it's operating.
Look at how Spring does it (in the sample applications like petstore that come with Spring), or better, look at the King/Bauer Hibernate-JPA book, which has a chapter on creating DAOs.