Dependency Injection in .NET: The Complete Mechanics

Dependency Injection shows up in nearly every ASP.NET Core project, usually as a few lines in Program.cs that get copy-pasted without much thought about what they actually do. This post goes all the way down to the real mechanics, what IServiceCollection actually is, what BuildServiceProvider does at the moment it runs, and exactly where and how a dependency gets resolved and handed to a class, using the Product API from earlier posts as the working example throughout. Dependency Injection, DI, is a technique where a class receives the objects it depends on from an external source, rather than