You may want to read the very interesting discussion of MVC/Cairngorm on Sho Kuwamoto’s blog:

http://kuwamoto.org/2005/08/16/mvc-considered-harmful/

Interesting Analysis…

Though you can access Databases more or less using Flex Data Services (now known as LiveCycle DataServices).

I am no expert, but I found the Commands to be great at encapsulating ALL of the code that affects the model away from the View or Delegate.

I think the delegates are good to be kept seperate from the Commands to allow for unit testing, also, it means that 99% of the code is handled in the command… which is immensely useful in debugging a complex application.

Jon,

Great write-up on Cairngorm. I’ve also wondered about a few of your points, but you definitely raised some new questions for me. Do you think that Cairngorm could be improved to better leverage the client-server model for a more “natural” SoC?

I would really like to see a response from a Cairngorm “expert” or someone on the development team. It’s always beneficial to see multiple perspectives.

Hey Jon,

I’m glad you are looking at Cairngorm. I’m working on an article about MVC in Flex. Sometimes Cairngorm is overkill. For simple applications with a single developer you can just use the Service Locator, Model Locator, Delegate, and Value Object patterns. But I think in most non-trivial Flex applications those are a minimum. If you are just using those patterns Cairngorm probably isn’t necessary but it might be helpful if you plan to someday be using Cairngorm in your app. Anyways, this is a great write-up! Thanks!

-James

I forgot to say… This blog helps me to know what to focus on in the article I’m writing. need… coffee…… too… early…

Thanks for the comment Mark.
To clarify a bit, Flex does not offer any client side ways of accessing a database that I am aware of. If they ever do, it seems to me that it would get a bit scary from a security perspective. As you said though, they absolutely have Flex Data Services (server side) for providing access to backend services like the db, thus the natural SoC I am referring to in the deployment model.

I couldn’t agree more. I ended up rolling one consisting of view, controller, dataManager (service and data tranformation in one), session (modelLocator + transient session data)

I come from a Flash / designer background, so here are my responses.

1. why do I need this level of abstraction when there is a natural SoC in the client-server like programming model of Flex?

Delegates are invaluable when your backend is:
A) not done
B) not using Remoting

For A, if the API changes, the rest of my app gets the same data, I only have to change 1 class per call.

For B, if I’m not using Remoting, I have to parse data and make ValueObjects out of it. The Delegate handles all this mess with Factories. Again, the rest of my app gets the same data, no matter what the data is (XML, URL encoded vars, etc.).

Commands are then allowed to focus on just data handling, typically the core of the app. Since the Views are bound to that data, this heavy lifting code is not polluted with data parsing.

I can see later you dig Business Delegates too. You must understand, though, Commands can get VERY hairy since you are doing the most important updateing and changing of data. Keeping these classes simple and short makes your most important code easy to read, upodate, and maintain.

2. why introduce a Front Controller into an event programming model like Flex?

Agreed. To me, it’s just a formality. There ARE people who build wrappers around this that address the concerns you talk about, hence Cairngorm v2.2 having the ability to use weak listeners as well as removing commands programmatically. I still feel it’s a leftover to make Java devs comfortable.

Hey Jon, interesting point of view…
Maybe you’d like to take a look to guasax framework(http://www.guasax.com/blog), we are working in a altenative to cairngorm for resolve the same problem.
I hope you found this information useful.

I’m a fan of using Delegates with Remoting.
I’m not sure how others are using them but my delegates basically mirror the DAO classes.
That way i have a client-side interface of the exposed DAOs.

Some areas of Cairngorm initally seemed overkill to me as well until I was assimilated and accepted that it is an industry standard framework and hopefully new developers coming into my project will find it easier to grasp because of their familiarity with Cairngorm.

I am always interested to read and try alternatives

I am just startig in Flex, interesting topics raised here

Overkill!!! Perhaps to pacify the Java fans. The Cairngorm just seems way to much for being practical. Value Objects are ok. It seems to me that Flex2 is naturally event driven, but some of these frameworks seem to complicate even the simplest of things.

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