1. Dependency Injection in .Net Core
Achieving Loose Coupling and High Cohesion
September 27, 2016

2. What is dependency injection?
Dependency injection is a technique for achieving loose coupling between objects and their dependencies
Rather than directly instantiating dependencies, the objects needed for a class are provided to them
Most often class will declare their dependencies via their constructor

3. Inversion of Control Containers
It is helpful to have a class dedicated to creating classes and dependencies
A container is a factory for providing instances of types that are requested from it
.NET Core has a simple built-in container that is represented by the IServiceProvider interface

4. Injection of a Simple Repository
An IStaffRepository is injected into a StaffController constructor
The ConfigureServices method of the Startup class is responsible for defining the services the application will use
services.AddTransient<IStaffRepository, StaffRepository>();

5. Service Life Times
Transient: Services are created every time they are requested
Scoped: Services are created once per request
Singleton: Services are created the first time they are requested. Each subsequent request uses the same instance

6. Example
An operation interface is defined with a with a unique identifier OperationId
One type per life time option is created
An OperationService is defined which which depends on each of the other operation types
It is used to clarify whether the this service is getting the same instance as the controller or a new one

7. Adding These to Configure Services
public void ConfigureServices(IServiceCollection services) { … services.AddTransient<IOperationTransient, Operation>(); services.AddScoped<IOperationScoped, Operation>(); services.AddSingleton<IOperationSingleton, Operation>(); services.AddTransient<OperationService>(); }

8. Resources
als/dependency-injection.html
pendencyInjectionDemo