[wildfly-dev] Favour jboss-persistence.xml if present

[Jason Greene]

On Jan 29, 2014, at 2:11 PM, Scott Marlow <smarlow at redhat.com> wrote:

> On 01/29/2014 02:44 PM, David M. Lloyd wrote:
>> On 01/29/2014 01:39 PM, Klein, Christopher wrote:
>>> Hey guys,
>>> I already filled out a feature request in JIRA (https://issues.jboss.org/browse/WFLY-2816).
>>> 
>>> We have the situation that our development environment (currently JBoss AS 7.1.1) differs from the production instance (WebSphere 8.5). Our persistence.xml has to be adjusted for production environment: different jta-data-source, different properties. The dirty solution for this problem would be to generate separate build artifacts for both environments. As you can imagine I don't like the idea of having two binaries just because of a few different settings. Other options (WildFly or WebSphere specific JPA properties; extending Hibernate persistence provider) do not work.
>>> 
>>> A much nicer solution would be: WildFly checks on deployment process for the existence of a jboss-persistence.xml. If it does, the jboss-persistence.xml is used for configuring the JPA subsystem. Otherwise it falls back to the standard persistence.xml. The jboss-persistence.xml would use the XML schema from persistence.xml.
>>> 
>>> I lookup into the WildFly sources and this change should be an easy patch which I would provide.
>>> 
>>> So here are my questsions:
>>> 1. Are you generally interested in accepting such a pull request or is it a feature you don't want?
>>> 2. Does another solution exists to my problem apart from generating different artifacts which makes this pull request needless?
>> 
>> It sounds like a reasonable idea that actually applies generally.  If I
>> recall correctly, we have something of a mix today of descriptors which
>> override versus supplementing existing configuration.  But overall the
>> unofficial policy for new descriptors has been to add them in to
>> jboss-all.xml as subdescriptors, FWIW.
>> 
> 
> I'm not sure that jboss-all.xml would be a good place for the 
> persistence unit definitions.

I would agree that this is probably impractical.

> 
> I think that the proposed jboss-persistence.xml (or 
> wildfly-persistence.xml) could be helpful for anyone that wants to only 
> develop on WildFly but deploy on other application servers.  I suppose 
> this could help someone that wants to migrate off of WildFly as well (to 
> prepare for a switch to something else).  Is that what you mean by the 
> proposed solution applying generally?

It does sound a lot like a vendor specific alt-dd feature. We have some other solutions as well that might be relevant:

1) Deployment overlay feature - This allows you to override the descriptors in a deployment without modifying the deployment. These are added in a separate management op with a match pattern, and preserved outside the lifecycle of the deployment. Available in WildFly 8 and EAP 6.2 (can’t recall if it made EAP 6.1).

2) Property Substituion - There is a flag you can optionally enable in standalone/domain.xml that allows descriptors to contain property expressions. However, this only works for this use case if all venders are using the same expression language (unlikely). I just thought I would mention it.


> 
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--
Jason T. Greene
WildFly Lead / JBoss EAP Platform Architect
JBoss, a division of Red Hat