Week 15 - Compound Design Patterns

Compound Design Pattern¶

Classification¶

• Compound: Multiple design patterns working together to solve a common problem.

Pattern Definition¶

• Definition: Multiple smaller design patterns working together to solve a common problem. It is only a compound design pattern if it has been used to solve multiple problems, not just because it uses multiple design patterns.

Representations¶

Mermaid Graph - MVC Pattern¶

UML¶

• Combination of:
  • Composite: View
  • Strategy: Controller
  • Observer: Model

MVC Usage¶

• View object is responsible for user input and output/presentation.
• The controller object implements the logic for the allowable transactions that can be performed on the model.
• The model object encapsulates the fine-grained business logic and data then notifies view/controller of updates.

MVC Sequence Diagram¶

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sequenceDiagram
    Web User->>+View: 1. Need some information
    View->>+Controller: 2. Handle Event/User Request
    Controller->>+Model: 3. Query Information
    Model-->>-Controller: 4. Result Set/Model Data
    Controller->>+Controller: 5. Validation
    Controller-->>-View: 6. Update the View
    View-->>-Web User: 7. Notify User

Real World Usages¶

• ASP.Net MVC
• Django
• Magento
• Spring

Java Code Example¶

• MVC Example Design Pattern

Main Take-Aways from the textbook¶

• The Model View Controller (MVC) Pattern is a compound pattern consisting of the Observer, Strategy, and Composite Patterns.
• The model makes use of the Observer Pattern so that it can keep observers updated yet stay decoupled from them.
• The controller is the Strategy for the view. The view can use different implementations of the controller to get different behavior.
• The view uses the Composite Pattern to implement the user interface, which usually consists of nested components like panels, frames, and buttons.
• These patterns work together to decouple the three players in the MVC model, which keeps designs clear and flexible.
• The Adapter Pattern can be used to adapt a new model to an existing view and controller.
• MVC has been adapted to the web.
• There are many web MVC frameworks with various adaptations of the MVC pattern to fit the client/server application structure.

Main OOP Principles of State Pattern¶

• All principles that apply to Strategy, Composite, and Observer Design Patterns.
• Loosely Coupled: Separation of concerns, the controller decouples the view from the model and vice versa.