Unidirection OneToMany causes duplicate key entry violation when removing from list ----------------------------------------------------------------------------------- Key: HHH-1268 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1268 Project: Hibernate Core Issue Type: Bug Affects Versions: 3.1, 3.5.6, 3.6.0 Environment: 3.1 final MySql 4.1.14 using MYISAM tables Reporter: Rex Madden Assignee: Gail Badner Fix For: 3.2.x, 3.3.x Attachments: possible_solution.patch, src.zip Simple OneToMany parent/child relationship using the default table structure (2 tables and a join table) Add 3 children to the parent. Flush. Remove the first child. Flush throws error: Exception in thread "main" org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:69) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:202) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:230) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:143) at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:296) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:980) at UnidirectionalOneToManyRemoveFromListBug.main(UnidirectionalOneToManyRemoveFromListBug.java:27) 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:585) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:86) Caused by: java.sql.BatchUpdateException: Duplicate key or integrity constraint violation, message from server: "Duplicate entry '5' for key 2" at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1461) at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:58) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:195) ... 11 more The problem is that there is a unique key on the relationship table that gets violated. The session removes the last row in the relationship table, then attempts to rewrite the child_id's. It fails since there is a uniqueness constraint on that column.