Model View Controllers (MVC)

1. Model View Controllers (MVC) Barack Karavani

2. Outline • What is MVC? • Why use the MVC Pattern? • MVC and the Web • Benefits of MVC in Web Applications • Modern MVC Frameworks

3. What is MVC • MVC is a pattern • Patterns are commonality that we find amongst software • Architectural Pattern - Provide solutions to various issues in Software Engineering • Design Patterns - Provide solutions to repeated issues in Software Development • MVC solves common issues by separating important parts into three subsystems.

4. Why MVC • Decouple the interaction between user interfaces and data stores. • Provide a clear separation of concern between components. • Promote the development of reusable components.

5. MVC and the Web Model View Controller

6. Benefits of MVC in Web Applications • Websites and Web Applications are great candidates for the MVC Pattern. • Inherently clear distinction for models, views, and controllers. • Multiple frameworks exist in various languages which support and encourage the MVC Pattern and other great coding principles!

7. Popular MVC Web Frameworks • Open Source frameworks are actively being developed • Promote the MVC Pattern • Definitions of MVC may change depending on the framework philosophy, READ THE DOCS!

8. Popular MVC Web Frameworks • MVC Frameworks exist both on the client-side and server-side Client Side (JS): • Backbone • AngularJS • EmberJS Server Side: • Django (Python) • Laravel (PHP) • Rails (Ruby)

9. Benefits of MVC in Web Applications • By promoting the use of reusable components, we prevent ourselves from writing “spaghetti” code. • Spaghetti Code - One-off code which interleaves business logic (model/controller) with view responsibilities • Hard to maintain • Hard to read • Does not scale well • Provide commonly used tools to web developers

10. Example of Spaghetti Code <? if(($child_assent || $adol_assent) && $form['short_name'] == 'parental_consent' && $canEdit): ?> <div class="form-helpers"> <? else: ?> <div class="form-helpers hide"> <? endif; ?>

11. Common Tools • Active Record and Object Relational Mapping (ORM) • Routes • Templating • Form and Input Validation • Security and Authentication • Testing & Test Cases

12. Views in Laravel, Django, Rails • Typically views for web applications consist of the HTML/CSS/JS side of things • Do not interact directly with the model • All three frameworks implement their version of a templating system. • Contain either simple logic or none at all • Prevents spaghetti code (by not allowing ANY code) • Promotes developing small templates to be reused and combined in multiple places

13. Templating {% if latest_poll_list %} <ul> {% for poll in latest_poll_list %} <li>{{ poll.question }}</li> {% endfor %} </ul> {% else %} <p>No polls are available.</p> {% endif %} <% @books.each do |book| %> <tr> <td><%= book.title %></td> <td><%= book.content %></td> </tr> <% end %> Django Rails

14. Models in Laravel, Django, Rails • Models are defined as objects. • Instances of models represent rows within the database table. • Frameworks will automatically build database tables based upon models. • Controller can interact with the models as native language objects.

15. Controllers in Laravel, Django, Rails • Controllers are functions that are called when a user accesses certain pages. • One controller can be called for multiple URLs. • Processes input data from the user. • Returns data to be styled in the view for the user to interpret.

16. Questions?