LazyInitializationException on REST services

[jmiddleton]

Hi All,

Checking the code, I realised that REST services can throw LazyInitializationException when the code is trying to access a relationship. The transaction has been completed but the code is accessing a lazy relationship which requires a transaction.

To replicate the issue, in web.rest.AccountResource.getAccount(HttpServletResponse) I added the following line:

log.debug("User authorities size: " + user.getAuthorities().size());

Then, I logged in the app and in the log I saw the following exception:

[ERROR] ar.com.tunuyan.conf.DispatcherServletConfiguration - An error has occured: failed to lazily initialize a collection of role: ar.com.tunuyan.domain.User.authorities, could not initialize proxy - no Session
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: ar.com.tunuyan.domain.User.authorities, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:566)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:186)
at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:137)
at org.hibernate.collection.internal.PersistentSet.size(PersistentSet.java:156)
at ar.com.tunuyan.web.rest.AccountResource.getAccount(AccountResource.java:53)

[jdubois]

This is "normal" with JPA, if you access a lazy relationship outside of a transaction.

Normally, you should use a service layer, with a transaction. For instance, the UserService class is perfect for doing this job.

Now, I understand this is a pitfall with JPA, so we should work on two possible solutions (outside of documenting the issue):

• Using the Open Session In View pattern. This is not my favorite solution, as it is mostly a hack, and it's bad for scalability
• Have a look at the extended persistence context pattern. I'm not sure we can make it work correctly with JHipster, but this would be my favorite solution. See the "PersistentContext.EXTENDED" attribute on the persistence context.

[jdubois]

As I feared we can't use an extended persistence context with our stack.

So the only two options we have left is:

• Using the open session in view pattern. I don't like it, as it hides the problem from the developer: he should use JPA correctly.
• Letting people use JPA correctly: that's why I won't correct this issue. You have many ways to go around this problem, either by using eager relations or by using a transaction and a Spring service. That's how JPA is supposed to be used, and Spring controllers, in my opinion.

[jmiddleton]

Agree with you, I don't like open session view pattern coz some exceptions (db exceptions) are only detected when the transaction is committed which happens outside of the controller.

What about to provide an option during the generation of the app where the developer can automatically include or not a open session in view filter?

Thanks,
Jorge

[jdubois]

This could be a solution: I don't want to have too many options when generating the app, but some options come and go depending on how we evolve. For me this is not a very high priority option, but I'll see that in a couple of versions (I think we will lose some options soon)

[phstudy]

In fact, this is a pitfall with Hibernate, not JPA.