Reading-Notes

Dependency Injection & Repository Design Pattern

This topic is important to me because I want to have code that is reusable and more organized.

Retrospective 13

References

Dependency Injection

Repository Pattern

Repository Design Pattern

SOLID Principles

Why SOLID Matters

SOLID Principles in Pictures

Notes

Dependency Injection is a software design pattern used to manage dependencies between components in a more flexible and maintainable way. It involves providing external dependencies to a class rather than letting the class create them internally.

Key Concepts

• Dependency: A service or object that another class depends on to perform its tasks.

• Dependency Injection Container: A container or framework that manages the creation and lifetime of dependencies. It resolves and injects dependencies into classes that require them.

• Injection: The process of passing dependencies to a class from the outside, usually through constructor parameters or setters.

Benefits

1. Decoupling: Components are decoupled from their dependencies, making the codebase more modular and adaptable to change.

2. Testability: DI makes it easier to test components in isolation by injecting mock or test implementations of dependencies.

3. Flexibility: You can easily swap or change dependencies without modifying the dependent classes.

4. Readability: Dependencies are explicitly declared, enhancing code readability and understanding.

5. Maintainability: Changes to dependencies impact only the registration code, reducing the ripple effect of changes.

6. Inversion of Control (IoC): DI is a key part of IoC, where control over object creation is inverted to a central container.

How to Implement DI

1. Identify Dependencies: Determine which classes require dependencies to function properly.

2. Create Interfaces: Define interfaces for dependencies to enable loose coupling.

3. Configure Container: Set up a DI container or framework (e.g., ASP.NET Core’s built-in container) to manage dependencies.

4. Register Dependencies: In the container’s configuration, register interfaces with their corresponding implementations.

5. Inject Dependencies: In classes requiring dependencies, use constructor injection or property injection to receive the dependencies.

Types of Injection

1. Constructor Injection: Dependencies are passed through the constructor when creating an instance of the dependent class.

2. Property Injection: Dependencies are set as properties of the dependent class after its creation.

3. Method Injection: Dependencies are provided as parameters to methods where they are needed.

Best Practices

1. Use Interfaces: Depend on interfaces rather than concrete implementations to allow for flexibility and easy mocking.

2. Limit Container Usage: Only use the DI container at the composition root to maintain clear control over dependencies.

3. Keep Dependencies Simple: Dependencies should do one thing well and have a clear purpose.

Dependency Injection is a powerful pattern that improves code quality, testability, and maintainability. It encourages loose coupling and allows for better control over dependencies in complex applications.

Key Concepts

• SOLID Principles: SOLID is an acronym that stands for Single Responsibility Principle (SRP), Open-Closed Principle (OCP), Liskov Substitution Principle (LSP), Interface Segregation Principle (ISP), and Dependency Inversion Principle (DIP).

SOLID Principles

1. Single Responsibility Principle (SRP):
   • A class should have only one reason to change.
   • A class should have one primary responsibility.
2. Open-Closed Principle (OCP):
   • Software entities should be open for extension but closed for modification.
   • New features can be added without altering existing code.
3. Liskov Substitution Principle (LSP):
   • Subtypes must be substitutable for their base types without affecting program correctness.
   • Inheritance should not break behavior or contracts.
4. Interface Segregation Principle (ISP):
   • Clients should not be forced to depend on interfaces they do not use.
   • Smaller, more specific interfaces are preferable to larger, general ones.
5. Dependency Inversion Principle (DIP):
   • High-level modules should not depend on low-level modules. Both should depend on abstractions.
   • Abstractions should not depend on details. Details should depend on abstractions.

Applying SOLID Principles

1. Identify Responsibilities: Break down classes into single responsibilities.

2. Abstraction and Encapsulation: Use interfaces and abstract classes to define contracts and hide implementation details.

3. Inheritance and Polymorphism: Ensure that derived classes can be substituted for base classes without altering program behavior.

4. Dependency Injection: Design classes so that they depend on abstractions rather than concrete implementations.

Benefits

• Code Maintainability: SOLID principles lead to code that’s easier to understand, extend, and modify.

• Flexibility: Code adhering to SOLID principles can adapt to changing requirements and new features.

• Testability: SOLID code is more testable, as classes can be isolated and dependencies injected.

Practical Use Cases

• Large Codebases: Applying SOLID principles helps manage complexity and maintain large projects.

• Collaborative Development: SOLID principles facilitate collaboration among developers by promoting clean and modular code.

Conclusion

SOLID principles provide a guideline for designing well-structured, maintainable, and flexible code. By adhering to these principles, developers can create software that’s easier to maintain, extend, and test.

Things I want to know more about

I want to learn more about using Dependency Injection, and why I would use it for my projects.

I want to learn more about practicing SOLID principles so I can be a more proficient programmer.