Making Use of Dependency Injection in ASP.NET Core

One of the cool features in ASP.NET Core is support for the Dependency Injection software design pattern.

For developers working in Object-oriented programming and web services, dependency injection provides what Microsoft defines in documentation as valuable best practices to help:

  • Design services to use dependency injection to obtain their dependencies.
  • Avoid stateful, static method calls (a practice known as static cling).
  • Avoid direct instantiation of dependent classes within services. Direct instantiation couples the code to a particular implementation.

If you are not familiar with the concept Dependency Injection, Wikipedia provides this basic definition:

“… dependency injection is a technique whereby one object (or static method) supplies the dependencies of another object. A dependency is an object that can be used [as] (a service). An injection is the passing of a dependency to a dependent object (a client) that would use it. The service is made part of the client's state. Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern.

In Object-oriented programming, web services and Software Oriented Architecture (SOA), the goal is to use objects as building blocks of an application in a way that allows you to make changes by adding and removing objects rather than writing extensive code. As Wikipedia explains: “The intent behind dependency injection is to decouple objects to the extent that no client code has to be changed simply because an object it depends on needs to be changed to a different one.”

In Microsoft pages outlining the fundamentals of dependency injection, it offers a simple definition: “A dependency is any object that another object requires.”

Diving into the Documentation

For developers who specifically want to start using dependency injection with ASP.NET Core, Microsoft offers step-by-step documentation with code samples and simple demonstration apps.

On Microsoft’s ASP.NET Blog, Jeffrey T. Fritz, Microsoft .NET Program Manager explains the basics of documentationDependency Injection in ASP.NET Core, noting: “With ASP.NET Core, dependency injection is a fundamental tenet of the framework. All classes instantiated by the framework are done so through the container service that is maintained by the framework in a container and configured by default in the Startup/ConfigureServices method.”

Fritz reassures developers that the framework makes adopting dependency injection very straightforward: “ASP.NET Core makes it easy to get started with this design pattern by shipping a container that you can use with your application. Configure your application’s controllers, views, and other classes that are instantiated by the framework with parameters on the constructor method to have those types automatically created and passed in to your class.”

The blog contains code samples to illustrate how the design pattern works and points developers to Microsoft ASP.NET Dependency Injection documentation. The authors provide loads of code samples and offer the following recommendations to developers working with dependency injection:

  • Avoid storing data and configuration directly in the service container. For example, a user's shopping cart shouldn't typically be added to the service container. Configuration should use the options pattern. Similarly, avoid "data holder" objects that only exist to allow access to some other object. It's better to request the actual item via dependency injection, if possible.
  • Avoid static access to services
  • Avoid using the service locator pattern (for example, IServiceProvider.GetService).
  • Avoid static access to HttpContext (for example, IHttpContextAccessor.HttpContext).

That is just a sample of the detailed information available on that site.

Beyond the Basics

Once you have the basics down, Steve Smith, Microsoft MVP since 2002 and a founding member of the ASPInsiders, an external advisory group for the ASP.NET product team, provides insight on the MSDN site for Writing Clean Code in ASP.NET Core with Dependency Injection.

He notes that dependency injection is “an increasingly common technique in .NET development, because of the decoupling it affords to applications that employ it.”

“ASP.NET Core not only supports DI,” Smith writes, “it also includes a DI container—also referred to as an Inversion of Control (IoC) container or a services container. Every ASP.NET Core app configures its dependencies using this container in the Startup class’s ConfigureServices method. This container provides the basic support required, but it can be replaced with a custom implementation if desired. What’s more, EF Core also has built-in support for DI, so configuring it within an ASP.NET Core application is as simple as calling an extension method.”

More about ASP.NET Core

If you are looking for an enthusiastic endorsement and overview of ASP.NET Core, don’t miss Philip Japikse's Q&A on Hands-On with ASP.NET Core and EF Core in Visual Studio Magazine.

“I think ASP.NET Core is the biggest game changer in the history of Web development using the Microsoft stack,” asserts Japikse, Developer, Coach, Author, Teacher, Microsoft MVP and Visual Studio Live! presenter.

“Microsoft developers are no longer restricted to running their applications on Windows Server, but can essentially run anywhere,” he explains. “This brings in a myriad of options for deployment targets, including popular containers (like Docker) and lower cost (than Windows) Linux distros. This also opens up .NET as a viable option in those organizations that require development tools to run cross platform. In the past, .NET developers were shut out from those opportunities since Java was the only large-scale enterprise toolset that could ‘check the box’ regarding running cross platform.”

Posted by Richard Seeley on 08/09/2018

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