[hibernate-issues] [Hibernate-JIRA] Created: (HHH-2598) Mapping a collection of entities from two different classes with the same collection name results in duplicate backref property exception if collection keys are not null

[Guido Scalise (JIRA)]

Mapping a collection of entities from two different classes with the same collection name results in duplicate backref property exception if collection keys are not null
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                 Key: HHH-2598
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2598
             Project: Hibernate3
          Issue Type: Bug
          Components: core
    Affects Versions: 3.2.3, 3.2.2, 3.2.1
         Environment: Proven on Hibernate 3.2.2 and 3.2.3, PostgreSQL 8.2.3, WindowsXP, Java 1.5
            Reporter: Guido Scalise
         Attachments: backref.patch, Hibernate-bug.zip

Mapping a child entity collection from two different parent entities results in duplicate backref property exception when configuring the session factory if the collection keys are marked not null and the collection names are the same in both parents.

Log is: 
(cfg.Environment                     509 ) Hibernate 3.2.3
(cfg.Environment                     542 ) hibernate.properties not found
(cfg.Environment                     676 ) Bytecode provider name : cglib
(cfg.Environment                     593 ) using JDK 1.4 java.sql.Timestamp handling
(cfg.Configuration                   1426) configuring from resource: /hibernate.cfg.xml
(cfg.Configuration                   1403) Configuration resource: /hibernate.cfg.xml
(cfg.Configuration                   553 ) Reading mappings from resource : com/bbsw/tests/ParentA.hbm.xml
(cfg.HbmBinder                       300 ) Mapping class: com.bbsw.tests.ParentA -> PARENT_A
(cfg.Configuration                   553 ) Reading mappings from resource : com/bbsw/tests/ParentB.hbm.xml
(cfg.HbmBinder                       300 ) Mapping class: com.bbsw.tests.ParentB -> PARENT_B
(cfg.Configuration                   553 ) Reading mappings from resource : com/bbsw/tests/Child.hbm.xml
(cfg.HbmBinder                       300 ) Mapping class: com.bbsw.tests.Child -> CHILD
(cfg.Configuration                   1541) Configured SessionFactory: null
(cfg.HbmBinder                       2375) Mapping collection: com.bbsw.tests.ParentA.children -> CHILD
(cfg.HbmBinder                       2375) Mapping collection: com.bbsw.tests.ParentB.children -> CHILD
Exception in thread "main" org.hibernate.MappingException: Duplicate property mapping of _childrenBackref found in com.bbsw.tests.Child
	at org.hibernate.mapping.PersistentClass.checkPropertyDuplication(PersistentClass.java:459)
	at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:449)
	at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
	at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
	at HBTest.main(HBTest.java:17)


The problem seems to be originated during the second Collection binding pass in org.hibernate.cfg.HbmBinder, as the Backrefs and IndexBackrefs names are created like this:

(Excerpts from HbmBinder.java r10921 2006-12-05 14:39:12Z steve.ebersole at jboss.com, contained in the Hibernate 3.2.3.ga source)

line 2242:			IndexBackref ib = new IndexBackref();
line 2243:			ib.setName( '_' + node.attributeValue( "name" ) + "IndexBackref" );

and

line 2478:			Backref prop = new Backref();
line 2479:			prop.setName( '_' + node.attributeValue( "name" ) + "Backref" );

in both cases the node name value is the collection name. So for every collection that points to a child, Hibernate creates a backref property without considering the posibility of more than one entity declaring the same collection name.

I've patched the code to add the collection owner's entity name to the property name, and it worked without problems.

I'm attaching: 
* ParentA, ParentB and Child classes
* Mappings for ParentA, ParentB and Child
* hbm.xml file
* Main test case. (HBTest.java)
* Proposed patch in unified diff format.

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