[jboss-as7-dev] detecting JPA usage in AS7 applications...

[Scott Marlow]

On 06/10/2011 03:13 AM, Jaikiran Pai wrote:
> On Friday 10 June 2011 01:07 AM, Scott Marlow wrote:
>>
>> This is wrong I think.  We probably only need to look for the presence
>> of @PersistenceUnit @PersistenceContext and same in deployment
>> descriptors (which we currently also do).
> In earlier versions of JBoss AS, we used to (optionally) bind the
> EntityManager and the EntityManagerFactory to a global JNDI name within
> the server. This was a JBoss specific feature (@see
> jboss.entity.manager.jndi.name and
> jboss.entity.manager.factory.jndi.name in Table 3.1 here
> http://docs.jboss.org/ejb3/docs/reference/1.0.7/html/entityconfig.html).
> Do we still do this in AS7 or do we plan to do this? Probably allow them
> to bind to java:jboss/ namespace?

We already support some other global abilities to reference PUs in other 
applications ().  I'm not against adding support for the 
jboss.entity.manager.jndi.name + jboss.entity.manager.factory.jndi.name 
extension into AS 7.x.

>
> The reason I ask this is because if we introduce this feature, then just
> relying on @PersistenceUnit and @PersistenceContext annotations won't be
> enough, since users might lookup the EntityManagerFactory/EntityManager
> via JNDI and in such cases too we will require the JPA module
> dependencies to be added implicitly.

It would be nice if users had the ability to explicitly mark a 
deployment as an EE JPA deployment or not a EE JPA deployment.

>
>>
>> I don't want to inject the JPA dependencies just because there is
>> persistence unit definition (we can still parse it and have it available
>> for use).
>>
>> This might help us deploy native Hibernate applications that don't use
>> EE JPA.
> I haven't looked at the code related to this (yet), but I'm curious
> about how this works and whether this implicit Hibernate dependencies is
> going to cause any issues. So:
>
> 1) When we say, we are adding implicit JPA dependencies to the
> deployment, what exact modules are we adding? JPA spec API module
> (javax.persistence.* classes) is fine. Are we adding Hibernate module as
> a dependency too?

In JPADependencyProcessor, we are currently adding modules:

  javax.persistence.api
  javaee.api
  org.jboss.as.jpa
  org.hibernate
  org.javassist
  org.jboss.as.naming

We might not need all of these any more (javassist + naming especially).

>
> 2) If we are adding a implicit Hibernate dependency, then, is there an
> (easy) way for users to specify that this implicit Hibernate dependency
> *not* be added? That way, users can package their own version of

We should introduce a way for that to be expressed.  We currently don't 
have an easy way for users to specify that.  It might be as easy as 
detecting that a persistence provider is already packaged with the app. 
  I'd like a way to:

- Choose which persistence provider to use for deployment.
- use something like jboss-ignore.txt (used in earlier releases) to 
ignore the provider jar in a deployment
- Perhaps adding extensions for provider version tags.
- Add a provider toolkit, that allows additional metadata/tooling for 
using the provider on AS7+.  One question is whether the SPI for this 
belongs in the AS7 project (obvious advantages to that) or should be 
external.

> Hibernate within their deployments. Note that this is probably going to
> be pretty common question from users, because in AS7 we are shipping
> Hibernate 4.x version which isn't yet used by many applications.
> Hibernate 3.x is the stable version, so I believe users would want to
> package that version in their app and use it.

Either package it or share it as a top level deployment.  I looked at 
this a bit but pushed it off to 7.1 as it didn't seem to be a priority 
for AS 7.0.

>
> 3) If we are adding a implicit Hibernate dependency, then, is there an
> (easy) way for users to use a different JPA provider (like EclipseLink)?

Not yet but I want to get there soon.  We do keep a 
(PersistenceProviderResolver) global list of providers that could be 
made more dynamic (to at least support providers that are top level 
deployments).  We will need to introduce a persistence.xml version tag 
property, to uniquely identify different instances of the same provider 
class.


>
> -Jaikiran
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