Dependency Injection and Service Lifetimes in .NET Core

Dependency Injection (DI) simplifies software development by promoting loosely coupled code, aligning with the Dependency Inversion Principle of SOLID. In this guide, we'll explore how to implement Dependency Injection and delve into the significance of different service lifetimes in .NET Core applications.

What is Dependency Injection?

Dependency Injection involves providing dependencies to a class externally, facilitating dependency inversion. In simpler terms, it allows a class to receive its dependencies rather than creating them internally.

In .NET Core applications, Dependency Injection is extensively used, with the framework providing native support. Leveraging Dependency Injection offers various advantages:

  • Eliminates hardcoded dependencies, promoting flexibility in code modification.
  • Encourages loosely coupled code, simplifying maintenance, extension, and testing.
  • Enhances testability, allowing easier testing of loosely coupled code segments.
  • Facilitates parallel development, enabling developers to work on independent functionalities simultaneously.
  • Improves code readability and cleanliness.

Example of Dependency Injection

Consider the following code snippet:

public class CategoryService
    private readonly ICategoryRepository _categoryRepository;

    public CategoryService(ICategoryRepository categoryRepository)
        _categoryRepository = categoryRepository;

In this example, CategoryService relies on an interface ICategoryRepository, adhering to Dependency Injection principles. By injecting dependencies through the constructor, the code becomes decoupled from specific implementations, promoting flexibility and ease of modification.

DI Containers

Dependency Injection containers, such as the native container in ASP.NET Core, automate the process of creating and injecting dependencies. While ASP.NET Core provides its container, alternative options like Simple Injector and Autofac are also available.

Service Lifetimes

Service lifetimes dictate how long instances of services persist within the application. In .NET Core's Dependency Injection container, three lifetimes are available:

  1. Transient: Instances are created anew each time they are requested.
  2. Scoped: Instances are created once per request, promoting efficient memory usage in web applications.
  3. Singleton: Instances persist for the entire lifespan of the application, ensuring consistency across requests.

Practical Example

To illustrate the concept of service lifetimes, let's consider a web application with three classes: ExampleTransientService, ExampleScopedService, and ExampleSingletonService. Each class generates a GUID, and the application displays these GUIDs to visualize instance creation.

By examining the GUIDs generated, we observe:

  • Transient objects produce unique GUIDs upon each request.
  • Scoped objects yield identical GUIDs within the same request.
  • Singleton objects generate consistent GUIDs throughout the application's lifespan.


Dependency Injection enhances code maintainability, testability, and flexibility. Understanding and selecting appropriate service lifetimes is crucial for optimizing application performance. By grasping these concepts, developers can streamline development and ensure robust, scalable applications.

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