[OJB-developers] ojb-0.7.343 - Single table inheritance still broken

[<Dal...@bd...>]

I tried out my original code on OJB v0.7.343 and it appears single table
inheritance is still be broken, or at least the bug I was encountering still
exists. This specific bug shows up when you have descendent classes with
*additional* fields. None of the OJB inheritance test cases have descendent
classes with additional fields, so the bug never appears. This is strange,
because having a bunch of classes with the exact number of fields is an
unrealistic example of inheritance.

Anyway, this bug has to do with having a descendent with additional fields, for
example:

class Foo {
     public int id;
     public String ojbConcreteClass;
     public String foo_value;
     ....
}

class Bar extends Foo {
     public Date bar_date;
     ....
}

TABLE FOOBAR (contents)

ID   CLASS_TYPE     FOO_VALUE BAR_DATE
---- ----      ----      ----
1    'Foo'          'A Foo'        NULL
2    'Bar'          'A Bar'        02/03/2002

The repository.xml file maps Foo's fields to the first 3 columns, and Bar's
fields to all 4 columns. If I try to map this type of class hierarchy with OJB
and do a query for all instances of Foo, the first instance, which is *a Foo*,
will get read in fine. However, when OJB goes to read in the Bar instance, I get
this exception:

[ojb.broker.accesslayer.RsIterator] ERROR: 3
3
     at
ojb.broker.accesslayer.RowReaderDefaultImpl.readObjectFrom(RowReaderDefaultImpl.java:72)
     at
ojb.broker.accesslayer.RsIterator.getObjectFromResultSet(RsIterator.java:251)
     at ojb.broker.accesslayer.RsIterator.next(RsIterator.java:142)
     at
plprototype2.tests.SingleTableInheritanceTest.testSingleTableInheritance(SingleTableInheritanceTest.java:81)
     at java.lang.reflect.Method.invoke(Native Method)
     at junit.framework.TestCase.runTest(TestCase.java:166)
     at junit.framework.TestCase.runBare(TestCase.java:140)
     at junit.framework.TestResult$1.protect(TestResult.java:106)
     at junit.framework.TestResult.runProtected(TestResult.java:124)
     at junit.framework.TestResult.run(TestResult.java:109)
     at junit.framework.TestCase.run(TestCase.java:131)
     at junit.framework.TestSuite.runTest(TestSuite.java:173)
     at junit.framework.TestSuite.run(TestSuite.java:168)
     at junit.textui.TestRunner.doRun(TestRunner.java:74)
     at junit.textui.TestRunner.start(TestRunner.java:234)
     at junit.textui.TestRunner.main(TestRunner.java:112)
     at
plprototype2.tests.SingleTableInheritanceTest.main(SingleTableInheritanceTest.java:39)
[plprototype2.tests.SingleTableInheritanceTest] INFO: Inheritance query failed!
java.util.NoSuchElementException
     at ojb.broker.accesslayer.RsIterator.next(RsIterator.java:151)
     at
plprototype2.tests.SingleTableInheritanceTest.testSingleTableInheritance(SingleTableInheritanceTest.java:81)
     at java.lang.reflect.Method.invoke(Native Method)
     at junit.framework.TestCase.runTest(TestCase.java:166)
     at junit.framework.TestCase.runBare(TestCase.java:140)
     at junit.framework.TestResult$1.protect(TestResult.java:106)
     at junit.framework.TestResult.runProtected(TestResult.java:124)
     at junit.framework.TestResult.run(TestResult.java:109)
     at junit.framework.TestCase.run(TestCase.java:131)
     at junit.framework.TestSuite.runTest(TestSuite.java:173)
     at junit.framework.TestSuite.run(TestSuite.java:168)
     at junit.textui.TestRunner.doRun(TestRunner.java:74)
     at junit.textui.TestRunner.start(TestRunner.java:234)
     at junit.textui.TestRunner.main(TestRunner.java:112)
     at
plprototype2.tests.SingleTableInheritanceTest.main(SingleTableInheritanceTest.java:39)

What's happening is that OJB is getting the definition for the number of fields
to expect from Foo's mapping definition, but Foo has only been defined with 3
columns: ID, CLASS_TYPE, and FOO_VALUE. When it reads in the Bar instance, the
RowReader returns an array of *4* columns: ID, CLASS_TYPE, FOO_VALUE, and
BAR_DATE. When it tries to initialize the BAR_DATE value into the object, it
goes past the 3 items in the Foo mapping definition and the system throws the
java.util.NoSuchElementException. The only way inheritance works is if Foo and
Bar had exactly the same fields, like this:

class Foo {
     public int id;
     public String ojbConcreteClass;
     public String foo_value;
     public Date bar_date;
     ....
}

class Bar extends Foo {
}

But of course, this is not inheritance at all and contrary to how most real
inheritance trees look. It is my suspicion that this may be a sticky bug to fix,
but I hope I'm wrong. Anyway, let me know if this makes any sense or not.

Dale Davis