I have worked with Code Igniter almost exclusively for the last nine months. In that time, I have found it to be a massive step ahead over working with some of the major CMS systems on the market (WordPress, I am looking at you). Nevertheless, there remains some major architectural and blind spots that exist in CodeIgniter as a framework. Some of these issues are resolvable (CodeIgniter’s presumption that you would only ever want to validate the POST superglobal), while others are inherent in it’s design. In this series I hope to look at some of these issues that I have found with CodeIgniter, showcase work-arounds where I can, or simply rant where no good solution exists. Today’s topic will be of the latter variety.
The God Object AntiPattern
Lets dip over to WikiPedia for the definition of a God Object:
In object-oriented programming, a god object is an object that knows too much or does too much… a program’s overall functionality is coded into a single “all-knowing” object, which maintains most of the information about the entire program and provides most of the methods for manipulating this data. Because this object holds so much data and requires so many methods, its role in the program becomes god-like (all-encompassing). Instead of program objects communicating amongst themselves directly, the other objects within the program rely on the god object for most of their information and interaction.
The God Object in CodeIgniter
CodeIgniter started as an early MVC framework that has maintained backwards compatibility with PHP5.2. It’s maintainers have insisted on maintaining this compatibility which has limited CI from taking advantage the advances that PHP5.3, 5.4, and 5.5 introduced to the language.
There remains nothing truly wrong with PHP5.2. While 5.3+ offers us many great advantages, a SOLID framework is still possible using the older version. CI’s architectural issues do not stem necessarily from it’s usage of the older version but rather the violation of SOLID principles in archetyping it’s interpretation of MVC.
In CI we have the CI super class (the idea of a super class alone should be a
code smell) that is globally available via the
get_instance() function. This
returns an instance of
CI_Controller, our main application controller handling
the current request. This instance is our elusive beast. The God Object itself.
We’ll call this object CI from here on out.
In any one request there can be only one instance of CI – it is essentially a singleton responsible for:
- Loading models
- Processing the request
- Returning the response
Here is where we get into the meat and potatoes.
The CI object begins its life by loading resources, that is it begins by loading various models and libraries and maintaining links to each of them like so:
This code instantiates an instance of the news model and assigns a reference to news. It then instantiates an instance of events. In this manner every model that comes into existence during request process is held as a reference by the CI object and can be access latter on in the request, e.g.
Once more, something very peculiar is done during this process. CI not only instantiates an instance of the given model but it also copies these references to every subsequently loaded model.
Thus every object that is loaded in this manner becomes aware of every object that had been loaded up-to that point regardless of whether that object really needed access to the behaviors of those objects. The model becomes unnecessarily bloated and the difficulty of debugging the behaviors of a given model increases. Unintended behaviors might be caused not by the model itself but by the combination of that particular model and the order or selection of previously loaded models.
Examine a Model’s State? No way.
Take for example the simple act of using
var_dump to see the state of an
object in memory. If we were to
var_dump our instance of
news we might as
well call it a day as
news contains a reference to everything that has been
loaded into memory for our request. The server will proceed to dump the entirety
of our application to the screen for us to wade through!
No Public Property is Safe
A larger issue is the assigning of the references themselves. Since the first act of initiating the model object is to copy CI’s massive registry of references to the model any properties or references set in the model’s constructor is at the mercy of the controller overwriting the model. Take for example, the events model. Let’s say the following was in the constructor:
Following substantiation of the events object the Events object CI will
immediately overwrite the news property with it’s own instance of the news
property. Thus the events model would either need to make the news property
protected which would generate an error when CI attempts to
access it or we would always need to take care to keep our model properties from
existing in the same namespace as CI.
I actually ran into a horrible bug where this very thing happened. I had a class
Validator that I loaded in with the controller. I also intended each of
my models to load their own instances of the
Validator class and to initialize
their instances with own unique validation parameters. However, since the
controller had already loaded an instance of
Validator it immediately
overwrote each of my model’s
Validator’s forcing them all to use the same
instance of the class. The resolution to this problem was to have to name each
Validator something different, thus we had