[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3870) Hibernate proxies Groovy's getMetaClass method breaking proxies when used with Groovy

[Emmanuel Bernard (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=32973#action_32973 ] 

Emmanuel Bernard commented on HHH-3870:
---------------------------------------

One last question (hopefully). 

Assuming the unproxying of metaclass.

class A {
  String getName() { return name; }
}

class C extends A {
  String getFoo() {
    return "foo " + name;
  }
}

now someone does in Groovy
a.getFoo();
with the metaclass thingy, we call c.getFoo() which calls c.getName().
Now name is not loaded yet (lazy) => we are in trouble because we have bypassed the proxy. Right?

> Hibernate proxies Groovy's getMetaClass method breaking proxies when used with Groovy
> -------------------------------------------------------------------------------------
>
>                 Key: HHH-3870
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3870
>             Project: Hibernate Core
>          Issue Type: Bug
>    Affects Versions: 3.2.6, 3.3.0.CR1, 3.3.0.CR2, 3.3.0.GA, 3.3.0.SP1, 3.3.1
>            Reporter: Graeme Rocher
>            Assignee: Emmanuel Bernard
>            Priority: Critical
>
> Say you have a class hierarchy like A->B-C and you obtain a proxied instance of C
> {code}
> A a = session.load(A, 1L)
> {code}
> When Groovy invokes a method it looks up the objects metaclass by calling the getMetaClass() method on A. The pseudo code for Groovy method dispatch is something like:
> {code}
> a.getMetaClass().invokeMethod(a, "foo")
> {code}
> The problem is that the getMetaClass() method is being proxied onto the underlying instance of C so when a.getMetaClass() is called you get the MetaClass for the class C, but because of the way Hibernate creates proxies it is not an instance of C at all, but instead an dynamically created subclass of A. The result is you get an IllegalArgumentException that is hard to debug.
> In Grails we have worked around this by customizing Hibernate's proxy creation mechanism to not proxy the getMetaClass() method. The problem this mechanism is currently insanely difficult to customize and also usage of Groovy on its own outside of Grails is still broken with Hibernate (such as inside JBoss Seam)
> It would be great if one of two things could be done:
> a) Hibernate does not proxy the getMetaClass() method at all this could be done by modifying JavassistLazyInitializer and the associated cglib one as follows:
> {code}
> 	private static final MethodFilter FINALIZE_FILTER = new MethodFilter() {
> 		public boolean isHandled(Method m) {
> 			// skip finalize methods
> 			return !( m.getParameterTypes().length == 0 && (m.getName().equals( "finalize" ) || m.getName().equals( "getMetaClass" ) ));
> 		}
> 	};
> {code}
> b) The mechanism for creating proxies is made easier to customize so that the getMetaClass() method can be easily excluded via some configuration or something. However, this would still mean that out of the box Hibernate is broken when used with Groovy unless the solution a) is applied too

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