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From "Willis Blackburn (JIRA)" <>
Subject [jira] Commented: (OPENJPA-1804) NPE in line 1514
Date Tue, 21 Sep 2010 02:15:32 GMT


Willis Blackburn commented on OPENJPA-1804:


Maybe I'm not using the right terminology.  I understand that I can use OpenJPA in one of
four ways.  First, I can run the class enhancer during the build process.  Second, I can define
a Java agent when I run the JVM that will enhance the classes as they're loaded.  Third, if
I'm using Java 6, OpenJPA will install a classloader hook of some kind that will also enhance
the classes as they're loaded.  And fourth, if I'm running Java 5, OpenJPA will dynamically
build persistent subclasses of my entity classes.  In all cases we ultimately get classes
that extend PersistenceCapable, but in the first three strategies, the PersistenceCapable
classes are the application's own classes, while in the last case, they're subclasses of the
application's classes.  I understand that the fourth method (dynamically-generated subclasses)
has certain drawbacks, some by necessity (it not being possible to intercept field set operations
for example), and some because it is still experimental.  I believe that I'm using the third
method, Java 6 with the classloader hook.

That said, I did have to set openjpa.runtimeUnenhancedClasses=supported in order to get the
program to run at all.  Am I in fact using the Java 5 dynamic subclassing strategy?

> 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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