Dec
30
2008
Few days ago, I read a post (the post is a bit old) about the the design concept of fat model, skinny controller. After going through that post and this one, for few days I have been thinking and trying to analyze the implementation impact of the concept. I guess I have been petty much impressed after doing some research on the web and going through blogs of experts in this subject.
It won’t be wrong if MVC is called the de-facto pattern of developing web applications. But still, the implementation mechanism of MVC and understanding the overall logic of MVC can be different from developer to developer.
MVC, being mostly implemented in the presentation layer provide powerful mechanism to developers to reuse code (reusing could have been easy if there were only one language or platform to deal with but while developing web applications developers need to deal with many languages and technologies that may or may not integrate well with each other) and significantly apply the concept of object oriented principles and agile methodologies.
Most of the developers and their code I have encountered especially in the PHP seem to embrace the idea of putting business logic in the controller rather than in the model. They regard model as the way only to deal with CRUD operations. It is true that MVC frameworks like Cake and Symphony provide quite powerful ORM capabilities without the need of writing a single SQL query embedding the principles popularized by Rails i.e. convention over configuration, DRY and YAGNI.
But in my opinion, models should not be treated as the the component for dealing with CRUD operations. Model should be responsible for more than that. It’s also true that applying business logic only through models is almost kinda impossible. It’s something like coupling which needs to be reduced but can’t be eliminated completely.
I view controllers as a tunnel that should be responsible for accepting input from the view and passing to the model and accepting raw output from the model and passing it to the view. Making the controller petty fat could make the code difficult to re-use. In reality all these things are easier to say but making the best use of the MVC by making model responsible for most of the business logic and let controllers and views perform their native task can be quite difficult because of the complex nature of the web. Complexity in the sense that there are other languages and technologies as well in the same layer that needs to be integrated and be dealt with. For eg; Server side Flash / SilverLight components, JavaScripts and so on.
So I have been trying for few days to apply the concept of fat model and skinny controller and as expected facing some difficulties especially to make my model more responsible and controller more light or in other word more skinny. Since I was involved in that project from middle so, attaching the business logic only to the model seems quite impossible. So, I am looking forward to do some small project in MVC applying the concept of Fat Model and Skinny Controller.
Until then, I can not claim that this concept must be followed though I still believe this concept should be followed to write re-usable and loosely coupled code.
As usual it would be great if you provide comments and criticisms and I can also know if I am wrong or right.
Oct
15
2008
Model-view-controller (MVC) is both a design pattern and an architectural pattern used in software engineering. - Wikipedia
Historical Background
MVC was started by Ward Cunningham and Kent Beck who were working with SmallTalk and designing GUIs at Xerox PARC. The original implementation is described in depth in the influential paper Applications Programming in Smalltalk-80: How to use Model-View-Controller.
What is Pattern?
A pattern is a solution to a problem in a given context. Christopher Alexander says each pattern is a three-part rule which expresses a relation between a certain context, a problem, and a solution. Pattern in the software development was especially popularized from the publication of the book named Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides or often referred to as Gang of Four (GoF). Design patterns represents a solutions to problems that arise when developing software within a particular context.
What is MVC?
MVC can be defined as an architectural pattern that is used while developing interactive application on the web. As the name suggests there are three major components of MVC:
- Model: Encapsulates core data and logic. Model is often related with the business logic of the application. It knows all the data that needs to be displayed. It is always isolated from the User Interface (UI) and the way data needs to be displayed.
- View: It is the UI part of the application. It uses read-only methods of the model and queries data to display them to the end users. It may be a window GUI or a HTML page. View encapsulates the presentation of the data, there can be many views of the common data
- Controller: It acts as a interacting glue between models and views. It accepts input from the user and makes request from the model for the data to produce a new view.
How it works?
Advantages
- Separation of Concern: Since MVC has three components whose operations are quite isolated from each other. For example; people working on view part can concentrate only on the UI and the part visible to the end users; people working on model part can concentrate on the business logic and the functional requirements of the system or ‘What’ part of the system and finally people working on the controller section may have knowledge of both view and model section so that interaction between other two components could be made easily. There is clear designation of roles for each stakeholder of a system.
- Modularized Development: Modularization is the process of dividing any complex problem into smaller sub-modules and we human have been following this approach from the time unknown. In MVC, we divide our system into three parts in order to reduce complexity.
- Pattern based development: As defined in the earlier section, pattern is the proven solution for any problem in a particular context. MVC itself is a pattern implemented in the presentation layer where it handles user’s interaction (controller) with a particular model through view. MVC is a proven solution for many contexts especially interactive web applications so following it in order to build a system may be comparatively more effective and trust worthy.
- More Control over URLs: Almost all MVC based frameworks have the feature of URL routing that gives us more control over the URL we desire. For example; http://www.foo.com/prajwal/edit where ‘prajwal’ may be unique ID and ‘edit’ may be controller action.
- Maintainability and Code Reuse: The Modular design of MVC supports the design goal of reusable software. As MVC requires a definite rule and style for coding, the result can be much more maintainable and reusable software.
- Test Driven Development: By following MVC, one can easily tests each and every part of the system. Moreover, most of the MVC frameworks do have one or more built-in testing frameworks.
- Platform and language independent: MVC is simply a pattern which can be implemented in any language or any platforms. Most of the popular languages and platforms like Java, .NET, PHP, Ruby, Python have one or more MVC based frameworks. So you once you know the MVC funda, you can implement in the platform of your choice.
Disadvantages
- Adds additional level of complexity: MVC can increase the level of complexity of a system since. MVC requires in depth planning so, any wrong decision taken early could impact the whole application life cycle.
- More files to manage means more headache: This may be context dependent. Some people might feel odd when dealing withe more files. A MVC based system has comparatively more number of files than a non-MVC based system.
- Rigorous separation between the model and view can sometimes make debugging more difficult: In my experience, debugging a MVC application is still quite difficult as compared to a non-MVC application. I am talking about my experience while working with CodeIgniter, a PHP based MVC framework. But the same is not true when talking about ASP.NET MVC.
Implementations of MVC as web-based frameworks
.NET
PHP
Python
Ruby
Java
Conclusion
As the benefits of MVC out number the disadvantages, in my opinion one should follow this approach when creating interactive web applications with high degree of agility.
