Single Responsibility Principle

• A class has a single responsibility
• Avoids bugs
• Avoids merge conflict

Open Close Principle

• Open to extension, closed for modification
• Approaches
• Decorator Pattern
  • Instead of modifying an implementation, use polymorphism for a custom implementation
  • Dependency injection at run time
• Extension Methods

Liskov Substation Principal

• A child class can do everything a parent class can
• Wrong:
  • Adult -> Child class
• Correct:
  • Human -> Adult
  • Human -> Child

Interface Segregation Principle

• Avoid bloated interfaces
  • Interfaces with methods unused by all implementors
• Solution make finer grain interfaces

Dependency Inversion

• High level modules should not depend on low level modules, they should both depend on abstraction
• Wrong Service -> Repository
• Correct Service -> IRepository (interface)
  • Inject Repository instance when instantiating Service