Dependency Injection Pattern

Dependency Injection (DI) is a design pattern used in software development and primarily in object-oriented programming. It is a technique where one object supplies the dependencies of another object, rather than the object itself creating those dependencies. This approach is commonly used to implement loose coupling between software components and to facilitate easier testing and maintenance.

Usage Scenarios

1. Unit Testing: In unit testing, DI allows easy substitution of real dependencies with mock objects or stubs.
2. Modularity and Reusability: DI facilitates the separation of concerns by allowing modules to focus on specific functionalities.
3. Flexibility in Configuration: Different configurations (e.g., production, staging, testing) may require different implementations of dependencies.
4. Decoupling Components: DI helps decouple components by removing the responsibility of creating dependencies from the dependent classes.
5. Framework Integration: Many frameworks and libraries in modern development (e.g., ASP.NET Core, Spring Framework) integrate DI containers or support dependency injection natively.
6. Plugin Architecture: Applications that support plugins or extensions benefit from DI to dynamically load and inject dependencies for plugins.
7. Cross-Cutting Concerns: DI is useful for injecting cross-cutting concerns such as logging, caching, and security into multiple parts of an application.
8. Database Access and Repository Pattern: Repositories and data access layers benefit from DI to inject database connections or ORM (Object-Relational Mapping) dependencies.

Key Concepts

1. Dependency:
   • A dependent object relies on another object (dependency) for some functionality.
2. Injection:
   • The process of providing dependencies to a dependent object.
   • Dependencies are typically provided through constructors, properties, or methods.
3. Types of Dependency Injection:
   • Constructor Injection: Dependencies are provided through the constructor of the dependent class.
   • Setter Injection (Property Injection): Dependencies are provided through public setter methods or properties of the dependent class.
   • Method Injection: Dependencies are provided through method parameters when calling methods on the dependent class.