PreserveDataModel behaviour (2)

[Enrique Medina]

Hi again,

I have investigated another interesting behaviour about using PreserveDataModel, which makes my application crash (due to the way I'm working with data tables). Let me explain it to you in a straight-forward manner.

Currently, I use a session scoped bean to work with my objects (e.g. one bean to work with customer objects, one bean to work with the users, etc), due to the fact that I don't want to loose state between requests (yes, I know it could have been done using <t:saveState>...). So within all my session beans, I have defined a ListDataModel variable that holds the data model that is presented to the view every time the view is rendered (nothing strange here, I guess).

>From my views (JSP), I simply use:

<t:dataTable ...... value="#{sessionScopedWhateverBean.listOfObjectsAsListDataModel}" ....>

So whenever the view is rendered, the method "public DataModel getListOfObjectsAsListDataModel()" in my session scoped bean is invoked. Obviously, the first time it will be created, and the subsequent calls simply will return the existing object. Everything's fine here.

The problem comes when using PreserveDataModel because, as explained in the wiki I posted about working with PreserveDataModel, every object in my listOfObjectsAsListDataModel is added to a new ArrayList belonging to a new _SerializedDataModel object, which is the object being really serialized when saving the state by the JspStateManagerImpl. And why is it the problem? Think about the future restoring phase...

When a link is clicked inside the data table to work with a particular object, the event created as a consequence of the "clicked link" has the information about the exact row which has been clicked (specifically in its rowIndex attribute). Following, the state is restored, and the previously serialized data model (as a _SerializedDataModel object) is used to set the information about the "clicked row". What does this mean? It's as simple as this: the "clicked row" information is set on the restored object, so it is really set on the _SerializedDataModel object (nothing to be with our original ListOfObjectsAsListDataModel object).

When afterwards the broadcast calls our action method (the one associated with the link in the data table through usually an HtmlCommandLink tag), our session scoped bean has the original ListOfObjectsAsListDataModel object that was used to create the _SerializedDataModel object when saving the state. But with a definitive difference: the rowIndex from the event was set on the _SerializedDataModel object, not the one we have here now, i.e. our ListOfObjectsAsListDataModel object. And due to the fact that our ListOfObjectsAsListDataModel was used to create the _SerializedDataModel object, now it has its internal rowIndex attribute set to the last row plus one (obviously, as the saveState method iterates through the ListOfObjectsAsListDataModel list of objects to populate the _SerializedDataModel list of objects).

At the end, the result is a call to setRowIndex(last row + 1), which obviously does not exist, so a "IllegalArgumentException: row is unavailable" is thrown. On the other hand, if I don't use preserveDataModel, everything works perfectly, as the ListOfObjectsAsListDataModel object is the one used to save the state (not the _SerializedDataModel).

IMHO, the solution will be as simple as updating my ListOfObjectsAsListDataModel object with the _SerializedDataModel object when restoring the state. But I would like to hear the MyFaces' team experts about this possibility before going deeper into the code.

Is it feasible? Is it possible to work with the preserveDataModel together with a DataModel inside my bean and the getRowData() method? Is the use od preserveDataModel incompatible with using the getRowData() method inside my bean?

Looking forward to hearing your comments :-)