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ASP.NET MVC Basics

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Applying Software Design Principles

3:26 with James Churchill

In this video, we’ll learn about software design principles and how we can use them to improve the overall code quality of our controller.

As I mentioned at the end of the previous video, 0:00
something is amiss in our comic books controller class. 0:03
No worries, though. 0:07
In this video, we'll dissect the issue and propose a solution. 0:08
Here's our ComicsBooksController class. 0:13
Our controllers Detail action method is currently responsible for 0:15
creating the comic book model instance that we pass to our view. 0:19
Ideally, our controller wouldn't be concerned with that aspect of our app. 0:23
Why? 0:28
Let's take a look at a scenario. 0:29
Imagine that we had another method in another class that needed a comic book 0:31
model instance for Amazing Spider Man, number 700. 0:36
With our current implementation, we'd need to repeat this code in the second method. 0:41
Doing this would violate a design principle called DRY or 0:46
Don't Repeat Yourself. 0:50
So, how do we avoid repeating ourselves? 0:52
We move our code that creates a comic book model instance into its own method named 0:55
GetComicBook. 1:01
Now, any method in our website that needs an instance of that comic book model, 1:03
can call the GetComicBook method. 1:07
Eventually, we're going to need a method 1:10
that will return an array of comic books for our comic books list page. 1:13
We can put that method in a class along with the GetComicBook method. 1:18
We can think of this class as a central location, or repository, for 1:23
storing and managing our comic book model instances. 1:28
Let's name this class ComicBook Repository. 1:32
By organizing our data access code in this way, 1:36
we're implementing the Repository Design Pattern. 1:39
Creating a design where we don't repeat ourselves allows for 1:44
our classes to naturally be more tightly focused. 1:48
Each class should have a single responsibility, or concern, and 1:51
not overlap with any other classes on our website. 1:56
This is known as the separation of concerns design principle. 2:00
Separating concerns also helps make our website easier to maintain. 2:05
With our improved design, if we wanted how our comic book model instances are created 2:10
or retrieved, we'd only need to change the comic book repository class. 2:16
The MVC design pattern is also an example of 2:22
the Separation of Concerns Design Principle. 2:25
The model is concerned about our website's data and business logic. 2:28
The view is concerned about providing a visual representation of the model. 2:32
And the controller is concerned about processing requests and 2:38
preparing responses. 2:42
Separating our website's concerns using the MVC design pattern 2:44
makes our code easier to understand and more maintainable. 2:48
Software design principles represent a set of guidelines 2:53
that help us avoid running into problems with our code in the long run. 2:56
Across all software development platforms and languages, these principles have 3:01
originated from lots of developers solving the same problems over and over again. 3:06
There are other design principles, 3:13
aside from the ones that we've mentioned in this video. 3:14
See the teacher's notes for links to additional resources. 3:17
In the next video, let's add the comic book repository class to our project. 3:21