What is dependency injection with example in asp.net core

Real life example:

Absolutely, dependency injection (DI) has practical applications that extend beyond programming! Here's a real-life example to illustrate:

Imagine you own a restaurant:

* You depend on a variety of things to function (dependencies): ingredients (vegetables, meat, spices), equipment (ovens, stoves, refrigerators), and utilities (electricity, water).

* In a traditional, non-DI approach, you might directly buy everything yourself and manage it all. This can be inflexible.

How DI can benefit your restaurant:

Ingredient Suppliers: Instead of being stuck with one supplier, you could rely on multiple vendors depending on price, seasonality, or specific needs. This is like having an "IngredientProvider" interface that different suppliers can fulfill.

Equipment Maintenance: You might contract with a separate company to maintain your ovens and refrigerators. This injects a "MaintenanceService" dependency into your restaurant's operations.

Utilities: The electricity and water companies are external dependencies that your restaurant relies upon to function.

Benefits of DI in this scenario:

Flexibility: If a vegetable supplier raises prices, you can easily switch to another one. Similarly, if your oven breaks down, the maintenance service can fix it without affecting other operations.

Focus on Core Business:  You can focus on what you do best - preparing and serving delicious food - by outsourcing dependencies to specialists.

Scalability: As your restaurant grows, you can easily add more suppliers, maintenance staff, or utility connections.

This is a simplified example, but it demonstrates how dependency injection translates to the real world. By separating core functionalities from external dependencies, you gain flexibility, maintainability, and better focus on what truly matters for your business.

Practical 

Dependency injection (DI) is a design pattern used to implement inversion of control (IoC) in software development. In ASP.NET Core, dependency injection is built into the framework and allows you to inject dependencies into your classes rather than having the classes create their dependencies themselves.

Here's a simple example of how dependency injection works in ASP.NET Core:

Let's say you have a service interface `IMyService` and its implementation `MyService`. First, you need to register these services in the ASP.NET Core container during application startup, typically in the `ConfigureServices` method in your `Startup` class:

```csharp-code

public void ConfigureServices(IServiceCollection services)

{

    services.AddTransient<IMyService, MyService>(); // Transient lifetime service registration

}

```

In this example, `Transient` lifetime means that a new instance of `MyService` will be created every time it's requested.

Now, you can inject `IMyService` into your controller:

```csharp-code

public class MyController : Controller

{

    private readonly IMyService _myService;

    public MyController(IMyService myService)

    {

        _myService = myService;

    }

    public IActionResult Index()

    {

        var data = _myService.GetData();

        return View(data);

    }

}

```

In this controller, `IMyService` is injected into the constructor. When an instance of `MyController` is created, ASP.NET Core automatically resolves and provides an instance of `IMyService` (which is actually `MyService` due to the registration).

This approach makes your code more modular, testable, and easier to maintain, as it promotes loose coupling between components and allows for easier substitution of implementations.