Organized Code
and
Application Structure
Objectives
- Gain an appreciation for the extreme scale of industrial software projects.
- Define the term "Design Pattern"
- Define the components of the "MVC" design pattern:
- Model
- View
- Controller
- Design an application structure using "MVC"
Q1 Projects:
- Was it harder to make small changes?
- Did you ever realize you had made a bad decision that you had to fix?
- How did your code style affect your ability to add new features?
- How did the size of the project affect your coding process?
- Contrast this with the shorter assignments you've been used to.
Real Projects Are Huge
Word Press (legitimate huge company):
32,000+ commits
20+ active branches
500,000 lines of php
iLoveOpenSource (small open source project):
255+ commits
2 active branches
26,000 lines of code
Real Projects Are Huge
Kuma, the project powering MDN:
10,000+ commits
30+ active branches
500,000 lines of python, HTML, CSS & JS
Enterprise FizzBuzz, a parody of architecture gone wrong:
2000 lines of Java code to complete fizz-buzz
Managing Complexity
As projects grow adding features becomes harder.
- In order to keep developer efficiency high the structure must of a code base must also be managed.
- Projects are typically "refactored" when the complexity starts to seriously hamper developer effectiveness.
- The decay of code over time is often called "Technical Debt" and should be paid off regularly.
Managing Complexity
-
Developers also create mental models, and design patterns to manage complexity.
-
Many web frameworks (rails, django) force adherence to a specific design pattern
- Design Patterns, even when not strictly enforced, make it easier for developers to find specific pieces of code
Some Simple "Rules"
KISS: Keep It Simple, Stupid!
When you write a feature, ask yourself it could be done more simply.
DRY: Don't Repeat Yourself
If you see the same block of code more than 2 places, put it into a function and reuse it instead.
YAGNI: You Ain't Gonna Need It
If you think you might need something in the future, but you don't need it right now... You ain't gonna need it.
Design Pattern:
"a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations."
Design Pattern:
A design pattern is kind of like a cookie cutter. Any kind of delicious cookie can be cut into the same shape, but remain uniquely flavored.
"classes" and "instances" are such a popular design pattern that they've been built into many programming languages.
Design Pattern:
There are THOUSANDS of design patterns. Do some reading, common patterns for additional research are:
The Factory Pattern
The Singleton Pattern
Continuation Passing Style
Recursion :)
But these are all tabled for later.
Model View Controller
Possibly the most well known web server design pattern
View
Controller
Model
Model View Controller
The Data Model
- Defines the application data and it's structure
- Database tables are typically the 'source of truth' for the model
View
Controller
Model
Model View Controller
The View
- Represents anything seen by the user
- HTML files are an example of views
- Users might interact with the views
View
Controller
Model
Model View Controller
The Controller
- Handles all communication between the model and the view
- Routing is an example of a "controller" task.
View
Controller
Model
Model View Controller
Layered Cake Analogy
MVC applications are like a layered cake. All three layers must be assembled before the cake is complete, and for a bite of cake to be optimally satisfying, all three layers should be eaten at once.
So, why might this be good?
View
Controller
Model
How Do We Apply This?
- MVC applies to how we organize our code.
- We separate the code controlling each layer so that navigating through large code-bases is easier
- We separate the code so that changes to one aspect of the code don't have to cause cascading changes through the whole application
- It's better to actually have "layered cupcakes"
Introspection Time
Think about the Petshop application you.
Without writing any code, identify the components of this application as they fit into our three categories:
Model
View
Controller
Take 5 minutes to look at your own code and decide
Pairing Time
Think about the Petshop application.
Take 5 minutes to discuss with your neighbor what features of your application belong in which categories. Where do you agree and disagree?
Sharing Time
Think about the booklist application you built over the weekend.
Alright everyone, what do you think?
Planning Time
Think about the Petshop application.
We've identified some features. Lets design an application structure together that makes sense for the booklist in an MVC pattern.
Copy of Complexity & MVC
By Hamid Aghdaee
Copy of Complexity & MVC
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