I'm creating 2 not-persisted objects and they have the same persisted object as instance variable. if i try to persist the new objects, i got a Duplicate entry violation. i know what it means, but i don't know what is wrong. can you please look at these small classes and point what is missing? Thank you. @Entity | public class Gene implements java.io.Serializable { | @Id @GeneratedValue private Integer id; | | private String name; | | @OneToMany() | private List<CancerType> cancerTypes; | public Gene() { } | | // Setters and Getters | } Table CancerType is filled with some data after table creation! @Entity | public class CancerType implements java.io.Serializable { | @Id @GeneratedValue private Integer id; | | private String name; | | public CancerType(){ } | | // Setters and Getters | } And the main: Session session = new AnnotationConfiguration().configure().buildSessionFactory().getCurrentSession(); | session.beginTransaction(); | | Gene g1 = new Gene(); | g1.setName("name"); | Gene g2 = new Gene(); | g2.setName("name"); | | List<CancerType> cts = BasicDAO.session.createQuery("from CancerType").list(); | | g1.setCancerType(cts); | g2.setCancerType(cts); | | session.save(g1); | session.save(g2); | | session.getTransaction().commit(); | Output: Hibernate: select cancertype0_.id as id0_, cancertype0_.name as name0_ from CancerType cancertype0_ | Hibernate: insert into Gene (name) values (?) | Hibernate: insert into Gene (name) values (?) | Hibernate: insert into Gene_CancerType (Gene_id, cancerTypes_id) values (?, ?) | Hibernate: insert into Gene_CancerType (Gene_id, cancerTypes_id) values (?, ?) | 00:01:39,109 WARN JDBCExceptionReporter:77 - SQL Error: 1062, SQLState: 23000 | 00:01:39,109 ERROR JDBCExceptionReporter:78 - Duplicate entry '1' for key 1 | 00:01:39,109 ERROR AbstractFlushingEventListener:301 - Could not synchronize database state with session | org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update | at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71) | Exception in thread "main" org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update | at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71) | at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) | at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:253) | at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:235) | at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:143) | at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298) | at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) | at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:253) | at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:235) | at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:143) | at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298) | at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27) | at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000) | at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338) | at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106) | at tvsas1.Main.a2(Main.java:58) | at tvsas1.Main.main(Main.java:64) | Caused by: java.sql.BatchUpdateException: Duplicate entry '1' for key 1 | at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1237) | at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:936) | at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48) | at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:246) | ... 9 more | at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27) | at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000) | at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338) | at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106) | at tvsas1.Main.a2(Main.java:58) | at tvsas1.Main.main(Main.java:64) | Caused by: java.sql.BatchUpdateException: Duplicate entry '1' for key 1 | at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1237) | at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:936) | at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48) | at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:246) | ... 9 more | View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4060587#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...