In ASP.NET, Transient and Scoped are two different types of dependency lifetimes when working with Dependency Injection (DI). These lifetimes determine how instances of services are created and managed throughout the application's lifecycle. Here's the difference between them:

1. Transient

• Lifetime: A new instance of the service is created every time it is requested.
• Use case: Ideal for lightweight, stateless services that don't need to maintain any state between requests.
• Scope: Each time you request an instance, even within the same HTTP request, you get a new object.
• Example: A service that performs a small task like formatting a string or logging something specific to a method call.

  services.AddTransient<IService, ServiceImplementation>();

In this case, every time IService is injected, a new instance of ServiceImplementation will be created.

2. Scoped

• Lifetime: A new instance of the service is created once per request (or per scope). This means that within a single HTTP request or operation, the same instance will be used across different components.
• Use case: Ideal for services that need to maintain state throughout the duration of a single HTTP request (e.g., a service interacting with a database where you want to use the same instance throughout the request).
• Scope: The instance is created once per HTTP request (or explicitly defined scope). If multiple components within the same request ask for the service, they get the same instance.

  services.AddScoped<IService, ServiceImplementation>();

In this case, within a single HTTP request, every component requesting IService will get the same instance of ServiceImplementation.

Key Differences:

Choosing Between Them:

• Use Transient when the service does not need to hold state or depend on other services in a way that requires maintaining a single instance.
• Use Scoped when the service holds some state for the duration of a request (e.g., database contexts, services that rely on a single request lifetime).