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From "Willis Blackburn (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-1804) NPE in MappingInfo.java line 1514
Date Mon, 20 Sep 2010 16:00:44 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-1804?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12912556#action_12912556
] 

Willis Blackburn commented on OPENJPA-1804:
-------------------------------------------

Rick,

I just saw the error about there not being any metadata for java.lang.Object.  But I knew
what was causing the problem because I was pursuing a strategy of starting off with running
the enhancer on a single class with a single annotation (@Entity) and then gradually adding
annotations and classes until it stopped working.  It gave me that message after I re-added
the Set<HostName>, so I figured that it was unable to figure out what type was in the
Set.  I subsequently discovered the issue with Scala, which I entered here:

http://lampsvn.epfl.ch/trac/scala/ticket/3857

It would have been helpful if OpenJPA had reported why it was looking for metadata for Object.
 Like "No metadata was found for type 'class java.lang.Object' referenced from Organization.hostNames."
 Also, it might be worth handling missing metadata for Object specially;  it's more likely
that OpenJPA has encountered a raw collection type than that the developer really wants Object
to be persistent but has neglected to provide the metadata.

About the runtime enhancer, why even have it if it's half-baked?  It would be better to simply
remove it and make the code base that much simpler.  If it's there, then people will use it,
and if it doesn't work, then they'll wind up with a bad impression of OpenJPA that may not
be warranted.



> NPE in MappingInfo.java line 1514
> ---------------------------------
>
>                 Key: OPENJPA-1804
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1804
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: Enhance
>    Affects Versions: 2.0.1
>            Reporter: Willis Blackburn
>
> I am encountering a NPE at MappingInfo.java 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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