[jbossseam-issues] [JBoss JIRA] Updated: (JBSEAM-2219) Introduce way to retrieve proxy object of a Seam JavaBean Component

[Wolfgang Schwendt (JIRA)]

     [ http://jira.jboss.com/jira/browse/JBSEAM-2219?page=all ]

Wolfgang Schwendt updated JBSEAM-2219:
--------------------------------------

    Description: 
The EJB programming model requires that a Session Bean never passes a "this"-pointer to other client objects. Instead, 
javax.ejb.SessionContext provides a method getBusinessObject().   If a SessionBean wants to pass a reference pointing to itself to other clients, it first has to retrieve its own EJB object reference by calling SessionContext.getBusinessObject()  which it then can pass to other beans.     This reference returned by javax.ejb.SessionContext.getBusinessObject() is the equivalent to Java's this pointer.     
 
With respect to Seam's interceptor framework, such a feature is missing as far normal JavaBean components are concerned.  It leads to subtle programming errors:

Consider the implementation of   org.jboss.seam.framework.Query. getDataModel():
   /**
    * Wrap the result set in a JSF {@link DataModel}
    * 
    * Delegates to {@link DataModels#getDataModel(Query)}
    * 
    */
   @Transactional
   public DataModel getDataModel()
   {
      if (dataModel==null)
      {
         dataModel = DataModels.instance().getDataModel(this);
      }
      return dataModel;
   }
   

This method method passes a "this"-reference to the org.jboss.seam.faces.dataModels Seam-component.
But this can lead to a behavior not expected by the programmer.    If the (Entity)Query-component gets instantiated as a conversation-scoped component,   Seam wraps the ManagedEntityIdentityInterceptor around this component.
After each method invocation,  that is intercepted by the  ManagedEntityIdentityInterceptor, the  ManagedEntityIdentityInterceptor saves wrappers for all contained Entity references in the conversation context and sets the corresponding reference fields in the Seam component to null.

Now, consider again above implementation of Query.getDataModel().     Because a "this" pointer is passed to the dataModels-component,  any callback conducted by the datamodel-component won't be routed through the ManagedEntityIdentity interceptor.

This leads to a bug as described in JBSEAM-1814.   In order to fix that bug, we would have to change the implementation of Query. getDataModel().    Rather than passing a this pointer to the dataModels component, the correct implementation would be as follows:  ...


  was:
The EJB programming model requires that a Session Bean never passes a "this"-pointer to other client objects. Instead, 
javax.ejb.SessionContext provides a method getBusinessObject().   If a SessionBean wants to pass a reference pointing to itself to other clients, it first has to retrieve its own EJB object reference by calling SessionContext.getBusinessObject()  which it then can pass to other beans.     This reference returned by javax.ejb.SessionContext.getBusinessObject() is the equivalent to Java's this pointer.     
 
With respect to Seam's interceptor framework, such a feature is missing as far normal JavaBean components are concerned.  It leads to subtle programming errors:

Consider the implementation of   org.jboss.seam.framework.Query. getDataModel():
   /**
    * Wrap the result set in a JSF {@link DataModel}
    * 
    * Delegates to {@link DataModels#getDataModel(Query)}
    * 
    */
   @Transactional
   public DataModel getDataModel()
   {
      if (dataModel==null)
      {
         dataModel = DataModels.instance().getDataModel(this);
      }
      return dataModel;
   }
   

This method method passes a "this"-reference to the org.jboss.seam.faces.dataModels Seam-component.
But this can lead to a behavior not expected by the programmer.   ...




[To be completed, more editing follows]


> Introduce way to retrieve proxy object of a Seam JavaBean Component
> -------------------------------------------------------------------
>
>                 Key: JBSEAM-2219
>                 URL: http://jira.jboss.com/jira/browse/JBSEAM-2219
>             Project: JBoss Seam
>          Issue Type: Feature Request
>            Reporter: Wolfgang Schwendt
>
> The EJB programming model requires that a Session Bean never passes a "this"-pointer to other client objects. Instead, 
> javax.ejb.SessionContext provides a method getBusinessObject().   If a SessionBean wants to pass a reference pointing to itself to other clients, it first has to retrieve its own EJB object reference by calling SessionContext.getBusinessObject()  which it then can pass to other beans.     This reference returned by javax.ejb.SessionContext.getBusinessObject() is the equivalent to Java's this pointer.     
>  
> With respect to Seam's interceptor framework, such a feature is missing as far normal JavaBean components are concerned.  It leads to subtle programming errors:
> Consider the implementation of   org.jboss.seam.framework.Query. getDataModel():
>    /**
>     * Wrap the result set in a JSF {@link DataModel}
>     * 
>     * Delegates to {@link DataModels#getDataModel(Query)}
>     * 
>     */
>    @Transactional
>    public DataModel getDataModel()
>    {
>       if (dataModel==null)
>       {
>          dataModel = DataModels.instance().getDataModel(this);
>       }
>       return dataModel;
>    }
>    
> This method method passes a "this"-reference to the org.jboss.seam.faces.dataModels Seam-component.
> But this can lead to a behavior not expected by the programmer.    If the (Entity)Query-component gets instantiated as a conversation-scoped component,   Seam wraps the ManagedEntityIdentityInterceptor around this component.
> After each method invocation,  that is intercepted by the  ManagedEntityIdentityInterceptor, the  ManagedEntityIdentityInterceptor saves wrappers for all contained Entity references in the conversation context and sets the corresponding reference fields in the Seam component to null.
> Now, consider again above implementation of Query.getDataModel().     Because a "this" pointer is passed to the dataModels-component,  any callback conducted by the datamodel-component won't be routed through the ManagedEntityIdentity interceptor.
> This leads to a bug as described in JBSEAM-1814.   In order to fix that bug, we would have to change the implementation of Query. getDataModel().    Rather than passing a this pointer to the dataModels component, the correct implementation would be as follows:  ...

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