title: Hibernate many to many with extras columns delete parent
body: <p>I have two entities purchase and product, they have many to many relationship
  let's call purchaseProduct her is the DDL for purchaseProduct </p>
  
  <pre><code>CREATE TABLE purchaseproduct
  (
    idpurchaseproduct serial NOT NULL,
    idpurchase integer,
    idproduct integer,
    qty double precision,
    price double precision,
    CONSTRAINT purchaseproduct_pkey PRIMARY KEY (idpurchaseproduct),
    CONSTRAINT purchaseproduct_idproduct_fkey FOREIGN KEY (idproduct)
        REFERENCES product (idproduct) MATCH SIMPLE
        ON UPDATE NO ACTION ON DELETE NO ACTION,
    CONSTRAINT purchaseproduct_idpurchase_fkey FOREIGN KEY (idpurchase)
        REFERENCES purchase (idpurchase) MATCH SIMPLE
        ON UPDATE NO ACTION ON DELETE NO ACTION
  )
  </code></pre>
  
  <p>After performing a delete  to a purchase entity</p>
  
  <p>Here is the code of delete</p>
  
  <pre><code> public boolean delete(Purchase obj) {
          try {
              if (!session.isOpen())
                  session = DatabaseUtil.getSessionFactory().openSession();
              session.beginTransaction();
              Purchase purchase = session.get(Purchase.class, obj.getIdPurchase());
              session.delete(obj);
              session.getTransaction().commit();
              session.close();
              return true;
          } catch (Exception e) {
              e.printStackTrace();
              return false;
          }
      }
  </code></pre>
  
  <p>i got this error:</p>
  
  <pre><code>org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [model.Purchase#89]
      at org.hibernate.engine.internal.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:648)
      at org.hibernate.event.internal.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:101)
      at org.hibernate.event.internal.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:56)
      at org.hibernate.internal.SessionImpl.fireDelete(SessionImpl.java:921)
      at org.hibernate.internal.SessionImpl.delete(SessionImpl.java:860)
      at dao.PurchaseDAO.delete(PurchaseDAO.java:70)
      at controller.purchase.PurchaseController.btnDeleteClicked(PurchaseController.java:262)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:497)
      at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
      at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:497)
      at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
      at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1767)
      at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1653)
      at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
      at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
      at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
      at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
      at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
      at javafx.event.Event.fireEvent(Event.java:198)
      at javafx.scene.Node.fireEvent(Node.java:8390)
      at javafx.scene.control.Button.fire(Button.java:185)
      at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
      at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
      at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
      at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
      at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
      at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
      at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
      at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
      at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
      at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
      at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
      at javafx.event.Event.fireEvent(Event.java:198)
      at javafx.scene.Scene$MouseHandler.process(Scene.java:3758)
      at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3486)
      at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
      at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2495)
      at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:350)
      at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
      at java.security.AccessController.doPrivileged(Native Method)
      at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$350(GlassViewEventHandler.java:385)
      at com.sun.javafx.tk.quantum.GlassViewEventHandler$$Lambda$288/1705705333.get(Unknown Source)
      at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:404)
      at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:384)
      at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
      at com.sun.glass.ui.View.notifyMouse(View.java:927)
      at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
      at com.sun.glass.ui.win.WinApplication.lambda$null$145(WinApplication.java:101)
      at com.sun.glass.ui.win.WinApplication$$Lambda$38/2060456699.run(Unknown Source)
      at java.lang.Thread.run(Thread.java:745)
  </code></pre>