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From "Willis Blackburn (JIRA)" <>
Subject [jira] Commented: (OPENJPA-1804) NPE in line 1514
Date Tue, 21 Sep 2010 13:55:33 GMT


Willis Blackburn commented on OPENJPA-1804:

Rick, you asked, "Perhaps we need to have a stronger warning message when this feature is
enabled? ... or disable it all together?"

I saw on the roadmap that OpenJPA 2.1 will require Java 6.  I think that if OpenJPA is not
going to support Java 6, then there is no need to support working with unenhanced classes.
 The strategy of using the attach API to install the agent will work for casual users, and
the others can pass the agent on the command line, use the J2EE container hooks, or use the
build-time enhancer.  The behavior of OpenJPA when using unenhanced classes is different from
its behavior when using enhanced classes (no lazy loading, changes only detected at flush),
so anything that users actually develop in that mode is not going to be production-ready.
 At some point developers will have to figure out how to get the agent or the build-time enhancer
working and test their code under that configuration.  Given how easy it is to use the attach
API enhancer under Java 6, there's not a strong case for having a less-functional alternative.

Have I added enough comments to this issue yet?  I think I'm going for a personal record.

> NPE in line 1514
> ---------------------------------
>                 Key: OPENJPA-1804
>                 URL:
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: Enhance, UnenhancedClasses, usability
>    Affects Versions: 2.0.1
>            Reporter: Willis Blackburn
> I am encountering a NPE at line 1514.  I'm sorry I don't have time to
prepare a test case right now.  I'm not even 100% sure what is causing the problem, but it
seems to be something like this:
> I have classes Organization, Group, User, and AddressBook.
> Group has a reference (many-to-one) to Organization.
> I'm using field-level access and the Java 6 runtime enhancer.  (NOT the build-time enhancer
or the agent.)
> In ManagedClassSubclasser.prepareUnenhancedClasses, the code receives a list of Class
objects--the ones in persistence.xml.  They are not in the same order as they are in persistence.xml,
but I don't know if that's important.  The first one is Group.  During the processing of Group,
the code invokes ClassMapping.setTable to set the table name, which is "group_table."  This
comes from the @Table annotation of Group.  So far, so good.  Then the code does some additional
processing on the relationship mappings of Group, which include the reference to Organization.
 During the processing of that relationship, the code calls MappingInfo.mergeJoinColumn. 
On line 1367, the method calls rel.getTable.  The "rel" variable points to the ClassMapping
for Organization.  Remember that prepareUnenhancedClasses hasn't gotten to Organization yet--it's
still working on Group--and so I assume that this Organization mapping was created on-demand.
 However, rel.getTable returns null.  The Organization class has a @Table attribute, and I
can see that the table name has been loaded in the ClassMappingInfo instance attached to the
ClassMapping for Organization, however the table name has not yet been copied from ClassMappingInfo
to ClassMapping.  Later, the mergeJoinColumn method attempts to dereference the null table
name and generates the NPE.
> Bottom line:  When using the Java 6, runtime enhancer, if class A has a reference to
class B, and both classes have @Table annotations (at least), and class A is processed first,
then it produces a NPE.

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