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Hibernate version: 3.05

Mapping documents:

GroupOfApplicants.hbm.xml
<hibernate-mapping>
<class
name="org.tbag.dom.GroupOfApplicants"
table="GroupOfApplicants">
<id
name="id"
column="ID"
type="java.lang.Integer">
<generator class="sequence">
<param name="sequence">GroupOfApplicants_SEQ</param>
</generator>
</id>
<version
name="latestVersion"
column="LATEST_VERSION"
type="int"
unsaved-value="negative" />
<set
name="applications"
inverse="true"
cascade="save-update"
lazy="true"
sort="unsorted">
<key column="GROUP_OF_APPLICANTS_ID"></key>
<one-to-many
class="org.tbag.dom.Application" />
</set>
<set
name="customers"
table="CUSTOMER_GROUP_OF_APPLICANTS"
lazy="true"
cascade="save-update"
sort="unsorted">
<key column="GROUP_OF_APPLICANTS_ID"></key>
<many-to-many
class="org.tbag.dom.Customer"
column="CUSTOMER_ID"
outer-join="auto" />
</set>
<property
name="lastUpdatedBy"
type="string"
update="true"
insert="true"
column="LAST_UPDATED_BY"
length="20" />
<property
name="lastUpdated"
type="date"
update="true"
insert="true"
column="LAST_UPDATED" />
</class>
</hibernate-mapping>

Application.hbm.xml
<hibernate-mapping>
<class
name="org.tbag.dom.Application"
table="Application">
<id
name="id"
column="ID"
type="java.lang.Integer">
<generator class="sequence">
<param name="sequence">Application_SEQ</param>
</generator>
</id>
<version
name="latestVersion"
column="LATEST_VERSION"
type="int"
unsaved-value="negative"/>
<property
name="applicationNumber"
type="java.lang.String"
update="true"
insert="true"
column="applicationNumber"/>
<property
name="existingCustomer"
type="boolean"
update="true"
insert="true"
column="existingCustomer"/>
<many-to-one
name="groupOfApplicants"
class="org.tbag.dom.GroupOfApplicants"
cascade="none"
outer-join="auto"
update="true"
insert="true"
column="GROUP_OF_APPLICANTS_ID"
not-null="true"/>
<property
name="lastUpdatedBy"
type="string"
update="true"
insert="true"
column="LAST_UPDATED_BY"
length="20"/>
<property
name="lastUpdated"
type="date"
update="true"
insert="true"
column="LAST_UPDATED"/>
</class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():
public void testSaveGroupOfApplicants()
{
// Setup fixture
BaseDAOHibernate groupOfApplicantsDAO = new GroupOfApplicantsDAO();

// deleteFromTables();

Application a1 = new Application();
a1.setApplicationNumber("num1");
a1.setExistingCustomer(true);

Application a2 = new Application();
a2.setApplicationNumber("num2");
a2.setExistingCustomer(false);

GroupOfApplicants goa = new GroupOfApplicants();
goa.addApplication(a1);
goa.addApplication(a2);

// Execute method under test
groupOfApplicantsDAO.saveObject(goa);

// Verify results
assertNotNull(goa.getId());
}

Full stack trace of any exception that occurs:

java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:782)
at java.util.HashMap$KeyIterator.next(HashMap.java:818)
at org.hibernate.engine.Cascades.cascadeCollection(Cascades.java:860)
at org.hibernate.engine.Cascades.cascade(Cascades.java:739)
at org.hibernate.engine.Cascades.cascade(Cascades.java:817)
at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:361)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:263)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:158)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:107)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:96)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:416)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:411)
at org.springframework.orm.hibernate3.HibernateTemplate$18.doInHibernate(HibernateTemplate.java:673)
at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:358)
at org.springframework.orm.hibernate3.HibernateTemplate.saveOrUpdate(HibernateTemplate.java:670)
at com.nr.infrastructure.dao.hibernate.BaseDAOHibernate.saveObject(BaseDAOHibernate.java:67)
at org.tbag.dom.GroupOfApplicantsTest.testSaveGroupOfApplicants(GroupOfApplicantsTest.java:40)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at junit.framework.TestCase.runTest(TestCase.java:154)
at junit.framework.TestCase.runBare(TestCase.java:127)
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:118)
at junit.framework.TestSuite.runTest(TestSuite.java:208)
at junit.framework.TestSuite.run(TestSuite.java:203)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:478)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:344)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

Name and version of the database you are using: Oracle 10.1.0.2.0

Other comments:
Note GroupOfApplicants object uses a HashSet, as the implementation of the Set used to reference associated Application objects.

I have done some investigation and run some tests and have discovered the following:
1. If there is only one Application object injected into the GroupOfApplicants object the code works.
2. If I remove the "version" properties from both GroupOfApplicants and Application hbm files (and the database) then this code works.

you iterate in set and hibernate (or you) change value in iterator (probably)
try leave version, but remove unsaved-value and see if work then