Tuesday, December 2, 2008

GXT Tree and Loading ... Alternative Design

This is a followup blog to my previous blog entry on GXT Tree and Loading from Restful URLs. While this approach worked, I had concerns over the number of AJAX requests as the tree is fully "expanded". As well, I was considering another possible issue:
  • The BaseModel objects representing the Country, Album objects are used elsewhere in the client (not just within my tree).
In this sense, the tree model is really a "view" into the real data. Having the tree be dynamically loaded prevents me from really being able to easily sync up changes made to the real data used elsewhere. I had already recognized that I likely needed to provide a singleton store pattern for obtaining countries and albums. The only problem was I was using this for lists and selection drop-downs which are modeled as ListStores (which co-incidentally are incompatible with TreeStores). However the fact that I have data being manipulated in two places just seems rather dangerous to me. For this reason, I think the process I intend to use here is still to use a DataProxy for the TreeStore, but instead have it's load method pull values from the corresponding singleton CountryStore and AlbumStore, and then provide some form of a Binder such that I can bind my TreeStore to the CountryStore (thus when a Country is created, deleted or modified, the TreeStore will be notified of the change in the CountryStore and take appropriate action). This also means I might be able to use a lighter-weight "representation" of the Country in the Tree (for example, just the "name" (for display) and "id" (as the foreign key to the CountryStore). In this case, my tree would really boil down to a BaseTreeModel object with three attributes ("name", "id", "type"). I'd want the type so that I can:

  1. Know the singleton store to access (if I need to full model)
  2. Toggle/display to proper icon in the tree
  3. Handle the leaf/childless cases (such as for Country)
One challenge in this case is I would need to ensure the AlbumStore, CountryStore and StampCollectionStore's are loaded prior to initializing/loading the tree store. As well, I would need to make sure the JSON output from the Album and StampCollection Restful Web Services includes an array of the ids of their children. (It actually is doing this today - but I bring this up as a point that others might consider). For example, an Album JSON String might look like the following:

In the above example, the album for Australia contains references to the countries 1104, 733 etc. If the StampTreeDataProxy came across a parent BaseModel which was an Album reference, I could obtain the concrete Album from the AlbumStore to get the Country references and thus create an output list for the Callback.onSuccess() method.

While this above approach will take me more time to implement, I think it will provide one major performance improvement. The tree building time is strictly driven by tree AJAX calls to obtain the concrete Country, Album and Stamp Collection data models, as opposed to "N" calls for each node in the tree. It would also give a consolidated view of the tree and allow management of the models to be controlled by their respective stores in a more uniform fashion.

Finally, using a ReferenceModel approach, I actually do not even need the DataProxy. I'd have to test this out, but it looks like I can simply use the TreeBinder to bind a Tree to a TreeModel, and the TreeModel can be built programatically once the singleton data stores are created.

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