Learning MVC (Model-View-Controller) Architecture In ColdFusion
by Ben Nadel (http://www.bennadel.com)
My application architecture is not great. While I know a great amount about ColdFusion at a technical level, my understanding of how things fit together in cohesive modules is not that strong. After talking to Steven Neiland at cf.Objective() 2012, I have a new enthusiasm for bringing my architecture skills up to par. This project is an exploration of a better MVC (Model-View-Controller) application architecture in which the controller is really a thin layer that does little more than moderate requests and responses.
Yes - Another ToDo Application
ToDo applications are the new "Hello World" apps in the programming world. They are simple enough to build, yet complex enough to teach some theory. I'll be trying to build a ToDo app using Model-View-Controller. While the app will only be used by a single person, I'll be building in a need to create an account for some added complexity and behavioral concerns.
At first, I was tempted to jump right into the code and start playing around. And, if you look at my GitHub history, you'll see that's exactly what I did. But, not knowing what the app was going to do, I felt completely frustrated and mentally blocked. So, yesterday, I went and actually created a lo-fidelity wireframe with InVision:
It has one basic layout; but, several different areas of concern.
The wonderful thing about having a wireframe is that you have a clear and obvious outline of basic user cases. The following outlines the actions that the user will be able to perform in the ToDo application based on the wireframe above.
- Request password reset.
- Reset password.
- Create a new account.
- Add new task.
- View existing tasks.
- View task detail.
- Update task.
- Delete task.
- Mark task as complete.
- View profile.
- Update profile.
Sometimes, in order to learn how to do something, you have to handicap yourself. To help me learn about separation of concerns and modularity and single-responsibility, I am going into this learning experiment without a database. All data will be cached within Gateway components for the life-cycle of the application. By doing this, I won't be tempted (or be able) to have database queries in places that they shouldn't be; in other words, I won't be able to have gateways that cut across too many tables. Nor will I have service objects that can mutate data caches that don't really belong to them.
All CFScript In The Controller (C) And Model (M)
For the past 10 years, I've been living in a tag-based world. This has made it very easy for me to mix my "controller" and my business logic and my data access. For this exploration, I'm going to go with nothing but CFScript in my Model and my Controller, leaving tags to only the View layer of the application. The intent here is to make it much harder to mix the different parts of the application; at least, it makes it harder to mix the views and the business logic.
What About Reporting?
I understand that, in reality, there are often different points of contact for a given set of data. Reporting is a good example of this. I wouldn't necessarily want my primary data gateways to be used for reporting; rather, I'd probably want a reporting gateway that can flatten, denormalize, and optimize queries for a particular outcome. In this app, however, there is no reporting - the point is to learn about tiered application architecture.
Architecture Notes And Random Thoughts
As I am going through this, I thought I would write down some random thoughts about the various aspects of the applicattion.
Data Gateways And Exceptions
As I'm working on the data access portion of the application stack (data gateways in this context), I've been grappling with whether or not to return a collection of entities; or, just to return a given entity. I like the idea of returning a collection, even when the intent is to find a single entity, as it allows me to always return non-NULL values from the gateway. If I don't return collections, then I am faced with a decision as to what should be done when a given set of data cannot be found? Should I return NULL? Should I throw an exception?
In the case of ColdFusion, the language itself doesn't have great support for NULL values. We now have the isNull() "function"; however, NULL values cannot be passed around. As such, it seems like an attempt to return a given value should result in a data-access exception if the given value cannot be found.
But, which functions of the data gateway layer should be considered to only load a single entity? Getting something based on its unique ID definitely feels like a single-object intent. But what about getting something based on a username and password? This might feel like a single-object intent; but, what if you can have inactive users? Who's to say that a given method will only ever return a single value?
Test-Driven Development (TDD)
I've never actually done anything with Unit Tests before. That's because I've never really organized things into proper "units" of work. For this learning project, I am going to try my hand at doing some test-driven development. First, on the server-side with MXUnit; and then, on the client-side with Jasmine.
For the first tests, I actually created my Model first (Task.cfc and Account.cfc) since I wasn't even sure what I wanted them to do - this is all so new for me. As such, I created my two test specifications (for them) as an afterthought. Hopefully, going forward, I'll try to start with my tests FIRST, and then move onto my green+refactoring steps second.