Dependency Injection - A C# Developer's Guide to DI Patterns

Define dependency injection as a set of software design patterns that implement the dependency inversion principle, enabling loose coupling by providing a dependency instance rather than creating it.

examine the tight coupling between the book service and the book repository and its maintenance and testing issues. advocate loose coupling via dependency inversion to improve testing and design flexibility.

Apply the dependency inversion principle to enable loose coupling between the business logic and data access via an abstract book repository interface, with Entity Framework Core and SQL Server migrations.

Learn method injection by passing an iBook repository as a method parameter to vary dependencies per method, while constructor injection remains the recommended approach.

Demonstrates property injection in a Blazor app, showing how a consumer injects a bookservice via an inject directive, wiring a repository through the Bookservice constructor, and highlighting composition root responsibilities.

Discover first dimension of dependency injection—object composition—where a composition route handles object creation, using either pure dependency injection or a DI container, paving the way for lifetime management and interception.

Register a singleton lifetime for the book service and iBook repository to create a single instance reused across the entire application and all HTTP requests.

Explore how the scoped lifetime creates one instance per scope (per http request) and reuses it within a request, then disposes it at the end.

discover how the transient lifetime creates a new dependency instance for every request, producing different hash codes and more garbage collection, and why it’s best for lightweight stateless services.

Explore dependency injection registration options such as singleton, scoped, and transient, with service type and implementation type, constructor injection, factories, and open generics across C# patterns.

Register groups of related services with a single extension method on IServiceCollection. Configure the Simple Book Catalog DbContext with AddDbContext and a lambda that calls UseSqlServer.

Learn to create a manual scope from a root service provider, resolve scoped services in a scope, and distinguish GetRequiredService from GetService in a DI container.

Enable scope validation to reveal how singleton lifetimes create captive dependencies on scoped services. See how the root provider blocks consuming scoped services from singletons and why lifetimes matter.