Advanced Dependency Injection Techniques in C#

Welcome to today's technical tutorial! We're back again with another article on dependency injection. In our 6th article in the Mastering C# series, we discussed a comprehensive guide to dependency injection in C# but this time, we will be exploring some advanced dependency injection techniques for better code.
Please stay tuned and enjoy!

Pre-requisites

To fully benefit from this article, readers should have the following prerequisites:

Basic Understanding of C#
- Familiarity with C# syntax, classes, interfaces, and object-oriented programming concepts like inheritance and polymorphism.
Introduction to Dependency Injection
- Understanding the basic concepts of Dependency Injection (DI), including how DI works, why it's used, and how it helps decouple components.
- Experience with injecting dependencies in a simple project (constructor injection, method injection, etc.).
Experience with ASP.NET Core
- Familiarity with creating and running ASP.NET Core applications, including setting up controllers, middleware, and basic services.
- Knowledge of how the built-in DI container works in ASP.NET Core (i.e., services.AddSingleton, services.AddScoped, services.AddTransient).
Understanding of Service Lifetimes
- Basic knowledge of service lifetimes (singleton, scoped, and transient) in ASP.NET Core and when to use each.
Experience with Creating and Registering Services
- Ability to register services in the Startup class or Program.cs and understand how services are injected into controllers or other components.
Familiarity with Generics and Interfaces in C#
- Basic understanding of how to work with generics and interfaces in C#, as these concepts are essential for advanced DI patterns.

Introduction to Dependency Injection
Deep Dive into the ASP.NET Core DI Container
Service Lifetimes in ASP.NET Core
Advanced Service Registrations
Conditional Resolution
Dependency Injection with Generics
Decorator and Interceptor Patterns
Using Third-Party DI Containers
Conclusion

Introduction to Dependency Injection (DI)

Dependency Injection (DI) is a design pattern used to manage and provide the dependencies that an object needs to perform its work. In simple terms, instead of an object creating its own dependencies, DI allows the necessary dependencies to be provided externally. This makes the code more flexible, testable, and easier to maintain.

Let’s break it down with an example.

Without Dependency Injection

Imagine you have a class called Car that depends on an engine to run. Without DI, the Car class would be responsible for creating the Engine object itself, which tightly couples them together.

public class Engine
{
    public void Start() 
    {
        Console.WriteLine("Engine started");
    }
}

public class Car
{
    private Engine _engine;

    public Car()
    {
        // Car creates its own Engine
        _engine = new Engine();
    }

    public void StartCar()
    {
        _engine.Start();
    }
}

In this case, if you want to change the Engine to a different type, you'd need to modify the Car class. This reduces flexibility and makes testing difficult.

With Dependency Injection

With DI, the Car class doesn’t create the Engine itself. Instead, the engine is injected into the Car class from the outside, making the Car class flexible and easy to test.

public class Engine
{
    public void Start() 
    {
        Console.WriteLine("Engine started");
    }
}

// Car class with injected dependency
public class Car
{
    private readonly Engine _engine;

    // Engine is injected via constructor
    public Car(Engine engine)
    {
        _engine = engine;
    }

    public void StartCar()
    {
        _engine.Start();
    }
}

Now, the Car class is not responsible for creating the Engine. This makes it easy to swap out the engine or use a mock engine during testing.

Using Dependency Injection in ASP.NET Core

In ASP.NET Core, DI is built-in, and you can register services (like Engine) in the DI container so that they can be injected where needed.

Here’s an example of how to set up DI in an ASP.NET Core application:

Register Services in Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Register Engine as a service
builder.Services.AddSingleton<Engine>();
builder.Services.AddTransient<Car>();

var app = builder.Build();

Inject Services in a Controller:

public class CarController : Controller
{
    private readonly Car _car;

    // Car is injected into the controller
    public CarController(Car car)
    {
        _car = car;
    }

    public IActionResult StartCar()
    {
        _car.StartCar();
        return Ok("Car started");
    }
}

Key Benefits of Dependency Injection:

Loose Coupling: Objects don't create their own dependencies, so you can easily swap them out.
Testability: You can pass mock objects for easier unit testing.
Maintainability: Changes to dependencies are centralized in one place, making your code easier to manage.

Dependency Injection simplifies code management by separating the creation of an object’s dependencies from its behaviour. ASP.NET Core provides a built-in DI container, making it easy to manage services and inject them throughout your application.

Deep Dive into the ASP.NET Core DI Container

Dependency Injection (DI) is one of the core features of ASP.NET Core, helping you manage dependencies between your classes. In this section, we'll break down how the ASP.NET Core DI container works, and how to use it effectively.

What is the DI Container?

The DI container in ASP.NET Core is responsible for:

Creating instances of your classes.
Managing the lifetimes of those instances.
Injecting dependencies into your classes automatically.

It’s part of the ASP.NET Core framework, so you don’t need to add anything extra to use it.

How to Register Services in ASP.NET Core

In ASP.NET Core, you register services with the DI container in the Startup.cs (or Program.cs in .NET 6+). Let’s go through the basics:

Registering a Service

To use a service in your application, you first need to register it with the DI container. This is typically done in the ConfigureServices method.

Example:

public interface IMyService
{
    void DoSomething();
}

public class MyService : IMyService
{
    public void DoSomething()
    {
        Console.WriteLine("Doing something...");
    }
}

// Registering the service
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddTransient<IMyService, MyService>(); // Registering IMyService
    }
}

AddTransient<IMyService, MyService>() tells the DI container that whenever IMyService is needed, it should create an instance of MyService.
You can also register services as Singleton, Scoped, or Transient.

Types of Service Lifetimes

ASP.NET Core provides three main service lifetimes:

Transient:
- A new instance is created each time the service is requested.
- Usage: Lightweight, stateless services.
- Code: services.AddTransient<IMyService, MyService>();
Scoped:
- A new instance is created once per request.
- Usage: Services that need to share data within a single request.
- Code: services.AddScoped<IMyService, MyService>();
Singleton:
- A single instance is created and shared throughout the application's lifetime.
- Usage: Services that maintain state or expensive to create.
- Code: services.AddSingleton<IMyService, MyService>();

How to Inject Dependencies

Once services are registered, ASP.NET Core automatically injects them into your classes. Here’s an example of injecting a service into a controller:

public class MyController : Controller
{
    private readonly IMyService _myService;

    // Injecting the service via the constructor
    public MyController(IMyService myService)
    {
        _myService = myService;
    }

    public IActionResult Index()
    {
        _myService.DoSomething(); // Using the service
        return View();
    }
}

In this example:

The IMyService is injected into the controller's constructor.
ASP.NET Core automatically provides the instance of MyService when the controller is created.

The ASP.NET Core DI container makes managing dependencies in your application easier and cleaner. By registering services with specific lifetimes and injecting them into your classes, you can create more modular and testable code.

Service Lifetimes in ASP.NET Core

In ASP.NET Core, services are managed by the Dependency Injection (DI) container. When you register services, you need to choose a service lifetime that defines how long a service object should live. There are three main types of lifetimes:

Transient Services

A new instance of the service is created every time it's requested.
Use when you need lightweight and stateless services.

Example:

// Registering a Transient service in Startup.cs or Program.cs
services.AddTransient<IMyService, MyService>();

When to use:

If you want a new instance each time, like when making HTTP requests.

Scoped Services

A new instance of the service is created once per request (HTTP request in web applications).
Use for services that should be shared within the same request, but not across requests.

Example:

// Registering a Scoped service
services.AddScoped<IMyService, MyService>();

When to use:

For database context services (like Entity Framework DbContext), where the service should be unique to each web request.

Singleton Services

A single instance of the service is created and shared throughout the application's lifetime.
Use for services that maintain state or perform heavy operations like caching.

Example:

// Registering a Singleton service
services.AddSingleton<IMyService, MyService>();

When to use:

For services that should be shared application-wide, such as caching, configuration, or logging services.

Choosing the Right Service Lifetime

Transient:
Use for stateless services or lightweight operations. For example, if your service makes an HTTP call, use Transient so each call is a fresh instance.
Scoped:
Use when you want a single instance per request. This is ideal for services like database contexts (EF Core) to ensure consistency throughout the request.
Singleton:
Use for services that should be shared across the application. Ideal for caching or any service that maintains state and needs to be used across requests.

Code Example

Here’s an example showing how to register different service lifetimes in Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Register services with different lifetimes
builder.Services.AddTransient<IMyService, MyService>();   // Transient
builder.Services.AddScoped<IMyScopedService, MyScopedService>();   // Scoped
builder.Services.AddSingleton<IMySingletonService, MySingletonService>();   // Singleton

var app = builder.Build();

app.Run();

Transient: New instance for each request.
Scoped: One instance per request.
Singleton: One instance for the application's entire lifetime.

By understanding these lifetimes, you can choose the best option based on how often you need new instances of your services!

Advanced Service Registrations

In more advanced scenarios, you may need to register multiple implementations of the same interface or resolve services based on certain conditions. Let’s explore how to do this.

Registering Multiple Implementations of an Interface

Sometimes, you may have more than one implementation of an interface and want to inject different versions of the service based on specific needs.

Example: Let’s say you have an interface IPaymentProcessor with two implementations: PaypalPaymentProcessor and StripePaymentProcessor.

public interface IPaymentProcessor
{
    void ProcessPayment(decimal amount);
}

public class PaypalPaymentProcessor : IPaymentProcessor
{
    public void ProcessPayment(decimal amount)
    {
        Console.WriteLine($"Processing {amount} via PayPal");
    }
}

public class StripePaymentProcessor : IPaymentProcessor
{
    public void ProcessPayment(decimal amount)
    {
        Console.WriteLine($"Processing {amount} via Stripe");
    }
}

Registering both implementations in the DI container:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IPaymentProcessor, PaypalPaymentProcessor>();
    services.AddTransient<IPaymentProcessor, StripePaymentProcessor>();
}

Injecting and using the services:

When you inject IEnumerable<IPaymentProcessor>, both implementations will be injected, and you can choose which one to use.

public class PaymentService
{
    private readonly IEnumerable<IPaymentProcessor> _paymentProcessors;

    public PaymentService(IEnumerable<IPaymentProcessor> paymentProcessors)
    {
        _paymentProcessors = paymentProcessors;
    }

    public void MakePayment(decimal amount)
    {
        foreach (var processor in _paymentProcessors)
        {
            processor.ProcessPayment(amount);
        }
    }
}

In this case, both PaypalPaymentProcessor and StripePaymentProcessor will process the payment.

Using Named Services or Keyed Service Resolution

Another advanced technique is resolving services based on specific names or keys. ASP.NET Core's default DI container doesn’t directly support named services, but you can achieve this with factories or by using other DI containers like Autofac.

Example: Here’s a simple workaround using a factory:

First, register your services:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<PaypalPaymentProcessor>();
    services.AddTransient<StripePaymentProcessor>();

    // Register a factory for keyed resolution
    services.AddTransient<Func<string, IPaymentProcessor>>(serviceProvider => key =>
    {
        switch (key)
        {
            case "PayPal":
                return serviceProvider.GetService<PaypalPaymentProcessor>();
            case "Stripe":
                return serviceProvider.GetService<StripePaymentProcessor>();
            default:
                throw new ArgumentException("Invalid payment processor key");
        }
    });
}

Inject and resolve based on the key:

public class PaymentService
{
    private readonly Func<string, IPaymentProcessor> _paymentProcessorFactory;

    public PaymentService(Func<string, IPaymentProcessor> paymentProcessorFactory)
    {
        _paymentProcessorFactory = paymentProcessorFactory;
    }

    public void MakePayment(string processorType, decimal amount)
    {
        var processor = _paymentProcessorFactory(processorType);
        processor.ProcessPayment(amount);
    }
}

Using the service:

var paymentService = new PaymentService(paymentProcessorFactory);

// Use PayPal processor
paymentService.MakePayment("PayPal", 100);

// Use Stripe processor
paymentService.MakePayment("Stripe", 200);

This allows you to inject a specific service based on the provided key, making it flexible to handle multiple implementations of the same interface.

Registering multiple implementations: Use IEnumerable<T> to inject and use all implementations of an interface.
Keyed or named service resolution: Use a factory method or a third-party DI container for resolving services based on a key or condition.

These techniques give you the flexibility to work with multiple implementations in a more advanced way!

Conditional Resolution in Dependency Injection (DI)

In Conditional Resolution, we choose which service implementation to inject based on certain conditions, like environment settings or business logic. Let's look at how this works in ASP.NET Core using factory methods to inject services dynamically.

Resolving Dependencies Based on Environment

Suppose we have two implementations of a service: one for development and one for production. Based on the environment, we want to inject the right service.

// Step 1: Create an interface
public interface IMessageService
{
    string SendMessage();
}

// Step 2: Create two implementations
public class DevMessageService : IMessageService
{
    public string SendMessage() => "Message from Development Service!";
}

public class ProdMessageService : IMessageService
{
    public string SendMessage() => "Message from Production Service!";
}

// Step 3: Register services in Startup.cs or Program.cs
public void ConfigureServices(IServiceCollection services)
{
    // Use conditional resolution based on environment
    if (Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Development")
    {
        services.AddSingleton<IMessageService, DevMessageService>();
    }
    else
    {
        services.AddSingleton<IMessageService, ProdMessageService>();
    }
}

In this example, the service is resolved based on the current environment. If you're running in Development, it will inject DevMessageService, and in Production, it will inject ProdMessageService.

Using Factory Methods for Dynamic Injection

Another approach is to use factory methods to resolve services dynamically, based on some condition at runtime (like a user role, a config setting, etc.).

// Step 1: Define your interface and implementations
public interface IPaymentService
{
    string ProcessPayment();
}

public class PayPalService : IPaymentService
{
    public string ProcessPayment() => "Payment processed using PayPal!";
}

public class StripeService : IPaymentService
{
    public string ProcessPayment() => "Payment processed using Stripe!";
}

// Step 2: Register a factory method for dynamic resolution
public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IPaymentService>(serviceProvider =>
    {
        var usePayPal = // Some logic to determine which service to use (e.g., from config)
            Environment.GetEnvironmentVariable("USE_PAYPAL") == "true";

        return usePayPal ? new PayPalService() : new StripeService();
    });
}

Here, the IPaymentService is resolved dynamically based on a condition (e.g., an environment variable or config setting). If USE_PAYPAL is set to true, the app will use PayPalService, otherwise, it will use StripeService.

How to Use These Services

Once the services are registered, you can inject them into controllers or other services:

public class HomeController : Controller
{
    private readonly IMessageService _messageService;
    private readonly IPaymentService _paymentService;

    public HomeController(IMessageService messageService, IPaymentService paymentService)
    {
        _messageService = messageService;
        _paymentService = paymentService;
    }

    public IActionResult Index()
    {
        var message = _messageService.SendMessage();
        var payment = _paymentService.ProcessPayment();

        return Content($"{message}\n{payment}");
    }
}

Conditional Resolution allows injecting different services based on conditions (like environment).
Factory Methods enable dynamic injection based on runtime logic.
These techniques add flexibility and adaptability to your DI setup.

Try these approaches and see how they make your app more dynamic and responsive to changes.

Dependency Injection with Generics

Handling Generic Types in Dependency Injection

In Dependency Injection (DI), generics allow you to create reusable and flexible services. Here’s a simple guide to handling generic types in DI with code examples.

Understanding Generics in DI

Generics let you define classes or methods with a placeholder for the data type. In DI, you can use generics to register services that work with different types without duplicating code.

Registering Generic Services

Example: Registering a Generic Repository

Let’s say you have a generic repository interface and its implementation:

// Generic repository interface
public interface IRepository<T>
{
    void Add(T item);
    T Get(int id);
}

// Generic repository implementation
public class Repository<T> : IRepository<T>
{
    public void Add(T item) { /* Add item to the database */ }
    public T Get(int id) { /* Retrieve item from the database */ return default(T); }
}

You can register this generic service in the DI container like this:

public void ConfigureServices(IServiceCollection services)
{
    // Registering a generic service
    services.AddTransient(typeof(IRepository<>), typeof(Repository<>));
}

In this example, AddTransient registers IRepository<T> with Repository<T>, allowing you to inject IRepository<T> into your classes.

Using Open and Closed Generic Registrations

Open Generic Registration: Registering a generic type without specifying the type parameter.

// Registering the open generic type
services.AddTransient(typeof(IRepository<>), typeof(Repository<>));

Closed Generic Registration: Registering a specific implementation for a particular type.

// Registering a closed generic type
services.AddTransient<IRepository<Product>, Repository<Product>>();

Here’s how you might use it in a class:

public class ProductService
{
    private readonly IRepository<Product> _repository;

    public ProductService(IRepository<Product> repository)
    {
        _repository = repository;
    }

    public void AddProduct(Product product)
    {
        _repository.Add(product);
    }
}

In this case, ProductService uses IRepository<Product>, and Product is the closed generic type.

Open Generic: Register the generic type itself (IRepository<>).
Closed Generic: Register the specific type (IRepository<Product>).

Using generics with DI helps keep your codebase clean and reduces redundancy. By understanding and using both open and closed generic registrations, you can create more flexible and maintainable applications.

Decorator and Interceptor Patterns in Dependency Injection

In this section, we'll explore how to use the Decorator and Interceptor patterns to enhance services and manage cross-cutting concerns in a beginner-friendly way.

Applying Decorators to Enhance Services

Decorator Pattern is used to add new functionality to an existing object without altering its structure. It’s great for adding features like logging, caching, or validation to services.

Example Scenario: Suppose you have a basic logging service, and you want to add extra logging functionality.

Basic Service Interface:

public interface IMessageService
{
    void SendMessage(string message);
}

Basic Service Implementation:

public class SimpleMessageService : IMessageService
{
    public void SendMessage(string message)
    {
        Console.WriteLine($"Message sent: {message}");
    }
}

Decorator Base Class:

public abstract class MessageServiceDecorator : IMessageService
{
    protected readonly IMessageService _inner;

    protected MessageServiceDecorator(IMessageService inner)
    {
        _inner = inner;
    }

    public abstract void SendMessage(string message);
}

Concrete Decorator:

public class LoggingMessageServiceDecorator : MessageServiceDecorator
{
    public LoggingMessageServiceDecorator(IMessageService inner) : base(inner)
    {
    }

    public override void SendMessage(string message)
    {
        Console.WriteLine("Logging: " + message);
        _inner.SendMessage(message);
    }
}

Registering Services in ASP.NET Core:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IMessageService, SimpleMessageService>();
    services.Decorate<IMessageService, LoggingMessageServiceDecorator>();
}

With this setup, any time IMessageService is used, it will now include logging functionality.

Using Interceptors for Cross-Cutting Concerns

Interceptor Pattern is used to handle cross-cutting concerns like logging, transaction management, or security in a centralized manner. Interceptors work by intercepting method calls and adding additional logic.

Example Scenario: Implement a logging interceptor to log method calls.

Interceptor Interface:

public interface IInterceptor
{
    void Intercept(IInvocation invocation);
}

Logging Interceptor Implementation:

public class LoggingInterceptor : IInterceptor
{
    public void Intercept(IInvocation invocation)
    {
        Console.WriteLine($"Calling method {invocation.Method.Name}");
        invocation.Proceed();
        Console.WriteLine($"Method {invocation.Method.Name} finished");
    }
}

Using Interceptors with Castle DynamicProxy:

To use interceptors, you'll need to install Castle DynamicProxy via NuGet:

dotnet add package Castle.Core

Creating a Proxy Factory:

public class ProxyFactory
{
    public static T CreateProxy<T>(T instance, IInterceptor interceptor)
    {
        var proxyGenerator = new ProxyGenerator();
        return proxyGenerator.CreateInterfaceProxyWithTarget(instance, interceptor);
    }
}

Registering Services and Interceptors:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IMessageService, SimpleMessageService>();
    services.AddTransient<IInterceptor, LoggingInterceptor>();
    services.AddTransient(provider =>
    {
        var interceptor = provider.GetRequiredService<IInterceptor>();
        var service = provider.GetRequiredService<IMessageService>();
        return ProxyFactory.CreateProxy(service, interceptor);
    });
}

In this setup, any call to IMessageService methods will be intercepted by the LoggingInterceptor, which logs the method calls and their results.

Summary

Decorators enhance existing services by adding new functionality, like logging, without changing the original service.
Interceptors handle cross-cutting concerns in a centralized way by intercepting method calls and adding additional logic.

These patterns help you manage and extend service behaviors in a clean, maintainable way.

Using Third-Party DI Containers

In ASP.NET Core, the built-in dependency injection (DI) container is quite powerful, but sometimes you might need additional features provided by third-party DI containers like Autofac or Ninject. This section provides a guide on how to integrate these third-party containers into your ASP.NET Core application.

Integrating Autofac with ASP.NET Core

Autofac is a popular DI container that offers advanced features. Here’s how you can integrate Autofac into an ASP.NET Core project:

Install Autofac Packages

First, add the necessary Autofac packages to your project. You can do this via NuGet Package Manager or using the Package Manager Console:
```
 Install-Package Autofac
 Install-Package Autofac.Extensions.DependencyInjection
```

Configure Autofac in Program.cs

Update your Program.cs file to use Autofac as the DI container:

 using Autofac;
 using Autofac.Extensions.DependencyInjection;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;

 public class Program
 {
     public static void Main(string[] args)
     {
         CreateHostBuilder(args).Build().Run();
     }

     public static IHostBuilder CreateHostBuilder(string[] args) =>
         Host.CreateDefaultBuilder(args)
             .UseServiceProviderFactory(new AutofacServiceProviderFactory()) // Use Autofac
             .ConfigureServices((context, services) =>
             {
                 services.AddControllers();
                 // Add other services
             })
             .ConfigureContainer<ContainerBuilder>(containerBuilder =>
             {
                 // Register Autofac modules or components here
                 containerBuilder.RegisterType<MyService>().As<IMyService>();
             })
             .ConfigureWebHostDefaults(webBuilder =>
             {
                 webBuilder.UseStartup<Startup>();
             });
 }

Register Services with Autofac

You can now register your services with Autofac in the ConfigureContainer method. For example:
```
 containerBuilder.RegisterType<MyService>().As<IMyService>();
```

Integrating Ninject with ASP.NET Core

Ninject is another popular DI container. Here’s how you can integrate Ninject:

Install Ninject Packages

Add the necessary Ninject packages to your project:

 Install-Package Ninject
 Install-Package Ninject.Extensions.DependencyInjection

Configure Ninject in Program.cs

Update your Program.cs file to use Ninject:

 using Ninject;
 using Ninject.Extensions.DependencyInjection;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;

 public class Program
 {
     public static void Main(string[] args)
     {
         CreateHostBuilder(args).Build().Run();
     }

     public static IHostBuilder CreateHostBuilder(string[] args) =>
         Host.CreateDefaultBuilder(args)
             .UseServiceProviderFactory(new NinjectServiceProviderFactory()) // Use Ninject
             .ConfigureServices((context, services) =>
             {
                 services.AddControllers();
                 // Add other services
             })
             .ConfigureContainer<IKernel>(kernel =>
             {
                 // Register Ninject modules or components here
                 kernel.Bind<IMyService>().To<MyService>();
             })
             .ConfigureWebHostDefaults(webBuilder =>
             {
                 webBuilder.UseStartup<Startup>();
             });
 }

Register Services with Ninject

Register your services in the ConfigureContainer method. For example:
```
 kernel.Bind<IMyService>().To<MyService>();
```

Integrating a third-party DI container like Autofac or Ninject with ASP.NET Core can give you access to advanced features and flexibility. Just install the necessary packages, configure the DI container in your Program.cs, and register your services. This setup allows you to leverage the strengths of these powerful DI tools while building your applications.

Conclusion

Here’s a quick recap of what we covered:

ASP.NET Core DI Container:
- We explored how the built-in DI container in ASP.NET Core works to manage and resolve dependencies.
Service Lifetimes:
- We discussed the three main service lifetimes: Scoped, Transient, and Singleton. Remember:
  - Scoped: Created once per request (ideal for database contexts).
  - Transient: Created each time they are requested (suitable for lightweight, stateless services).
  - Singleton: Created once and shared throughout the application (useful for services that maintain state).
Conditional Resolution:
- We learned how to resolve dependencies based on conditions, which allows for flexible and dynamic service creation.
Advanced Patterns:
- We covered more advanced DI patterns like decorators to add functionality to services and generics for working with flexible types.

Further Learning Resources

To continue expanding your knowledge, check out these resources:

Books: "Dependency Injection in .NET" by Mark Seemann
Courses: Pluralsight: Dependency Injection in .NET
Documentation: ASP.NET Core Dependency Injection

Thanks for following along. Keep experimenting with these techniques to build more flexible and maintainable applications. I hope you found this guide helpful and learned something new. Stay tuned for the next article in the Mastering C# series: Exploring C# Source Generators

Happy coding!

Advanced Dependency Injection Techniques in C#

Mastering Advanced Dependency Injection in C# for Better Code

Pre-requisites

Table of Contents

Introduction to Dependency Injection (DI)

Deep Dive into the ASP.NET Core DI Container

What is the DI Container?

Registering a Service

Service Lifetimes in ASP.NET Core

Transient Services

Scoped Services

Singleton Services

Advanced Service Registrations

Conditional Resolution in Dependency Injection (DI)

Dependency Injection with Generics

Handling Generic Types in Dependency Injection

Understanding Generics in DI

Registering Generic Services

Using Open and Closed Generic Registrations

Decorator and Interceptor Patterns in Dependency Injection

Applying Decorators to Enhance Services

Using Interceptors for Cross-Cutting Concerns

Using Third-Party DI Containers

Integrating Autofac with ASP.NET Core

Integrating Ninject with ASP.NET Core

Conclusion