XPages MVC: Experiment II, Part 4

Jun 4, 2012, 7:57 PM

Tags: xpages mvc
  1. XPages MVC: Experiment I
  2. XPages MVC: Experiment II, Part 1
  3. XPages MVC: Experiment II, Part 2
  4. XPages MVC: Experiment II, Part 3
  5. XPages MVC: Experiment II, Part 4

To finish up my series on the infrastructure of my guild forums app, I'd like to mention a couple of the down sides I see with its current implementation, which I'd generally want to fix or avoid if re-implementing it today.


One of the strengths of this kind of MVC setup is that it works to separate the front-end code from the data source. It would be (relatively) easy for me to replace the model and collection classes with versions that use a SQL database or non-Notes document storage should I so choose. That's a double-edged sword, though: because I'm not using any of the built-in data sources and controls with Domino knowledge, I had to do everything myself. This means a loss of both some nice UI features - like the rich text editor's ability to upload images inline - and the XPage data sources' persistence and caching features.

The collection code deals with View and ViewEntryCollection classes directly, but they can't be serialized, so I had to write my own methods to detect when the object is no longer valid (say, when doing a partial refresh) and re-fetch the collection. This was good in the sense that I learned more about what is and is not efficient in Domino. For example, getNthEntry(...) on a ViewEntryCollection grabbed via getAllEntriesByKey(...) is fast. Conversely, while retrieving data in a view is usually significantly faster than getting the same data from a document, there's a point where the view index size is large enough that, provided you're fetching only a few documents at a time, it's better to use the document. With a lot of work (and a LOT of collection caching), I ended up with something that's quite fast... but since I wrote all the code myself as part of a side project, it was also pretty bug-prone for the first couple weeks after deployment.

Maybe I'd be able to find ways to piggyback more on the built-in functionality if I re-did it, but, as it stands, it's kind of hairy.

Inconsistent Separation

This isn't a TERRIBLE problem, but I'm kind of annoyed with some of the inconsistent choices I made about where DB-specific code goes. For example, collection managers have very little Domino-specific code... except when they need to know about sorting and searching. Similarly, almost all of the code in the model objects deals with pure Java objects and the clean collections API... except the save() methods, which are big blobs of Domino API work. That makes some sense, but the model classes don't handle creation from the database - that's in the collection classes. Like I said, it's not the end of the world, and it's consistent within its own madness, but there are some weird aspects and internal leaks I wouldn't mind cleaning up.

Lack of Data Sources

This is sort of the flip side to my first problem. All of my collection managers are just objects and the collections are just Lists. This is good in the sense that these things work well in Server JavaScript and with all of the built-in UI elements, but it'd be really nice to write my own custom data sources so I can explicitly declare what data I want on the page - using a xp:dataContext or bit of JavaScript in a value property just feels "dirty", like I'm not embracing it completely. However, this problem isn't as much an architectural one as it is a lack of education - I haven't bothered to learn to write my own data sources yet (even though I expect it's more or less straightforward, for Java), so I could remedy that easily enough.

No Proper Controller

This is just another manifestation of the root cause that has me looking into all this MVC stuff to begin with. Even though my collections and models are better than dealing with raw Domino objects, there's still too much of a tie between the UI and the back-end representation, as well as the requisite dependence on the Domino HTTP stack to handle routing requests. Of course, I'm still working on the correct solution to this.


Overall, my structure as written has been serving me well. New data elements are pretty easy to set up - I wouldn't mind not having to write three classes per, but hey, it's Java - and working with them is a breeze. Though it took a while to get everything working, now that it is, I can make tons of UI changes without worrying much about the actual data representation. I can change the way data is stored or add on-load or on-save computation beyond the capabilities of Formula language without changing anything in the XPages themselves. So in those senses, my forum back-end code is a huge step up from doing it directly xp:dominoDocuments, but it still doesn't feel completely "right".

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