Understanding the Differences Between AddTransient, AddScoped, and AddSingleton Services in C#

AddTransient

The `AddTransient` method registers a service with a **transient** lifetime. This means that a new instance of the service will be created every time it is requested. Each time you resolve the service, you will receive a new instance.

Here's an example of using `AddTransient` to register a service:

services.AddTransient<ITransientService, TransientService>();

In the above code, `ITransientService` is the interface representing the service, and `TransientService` is the implementation of that interface. Whenever you request an instance of `ITransientService`, a new instance of `TransientService` will be created.

`AddTransient` is useful for lightweight and stateless services where a new instance is needed for each request. However, keep in mind that using `AddTransient` for services with heavy initialization or shared state can result in unnecessary overhead and might not be the best choice.

AddScoped

The `AddScoped` method registers a service with a **scoped** lifetime. A new instance of the service is created once per client request within the scope. In ASP.NET Core, the scope is usually equivalent to the lifetime of an HTTP request.

Here's an example of using `AddScoped` to register a service:

services.AddScoped<IScopedService, ScopedService>();

In this example, `IScopedService` represents the service's interface, and `ScopedService` is the corresponding implementation. When you resolve `IScopedService` within a particular scope, the same instance of `ScopedService` will be returned. However, different scopes will receive different instances.

`AddScoped` is commonly used for services that maintain state throughout a request. For example, if you have a service that tracks user-specific data during an HTTP request, using `AddScoped` ensures that the service maintains the state within that request's scope.

AddSingleton

The `AddSingleton` method registers a service with a **singleton** lifetime. A single instance of the service is created and shared across all requests throughout the application's lifetime.

Here's an example of using `AddSingleton` to register a service:

services.AddSingleton<ISingletonService, SingletonService>();

In this case, `ISingletonService` represents the service's interface, and `SingletonService` is the implementation. When you resolve `ISingletonService` anywhere in your application, you will always receive the same instance of `SingletonService`.

`AddSingleton` is suitable for services that are stateless or maintain shared state across the entire application. It's important to note that you should exercise caution when using `AddSingleton` with services that require thread safety or have mutable state shared across multiple requests.

Choosing the Right Lifetime

Now that we've covered the differences between `AddTransient`, `AddScoped`, and `AddSingleton`, let's discuss when to use each of these methods.

- Use `AddTransient` when you need a new instance of a service for every request or operation.

- Use `AddScoped` when you want to maintain state within the scope of an HTTP request or a defined context.

- Use `AddSingleton` when you want to share a single instance of a service throughout the entire application.

By choosing the appropriate lifetime for your services, you can ensure optimal performance and behavior in your application.

In this article, we explored the differences between `AddTransient`, `AddScoped`, and `AddSingleton` when registering services in C#. Understanding the lifetimes of your services is crucial for managing dependencies and ensuring proper behavior within your application. Remember to consider the characteristics of your services and their requirements to select the appropriate lifetime for each registration.

Published on Jun 1, 2023

Tags: ASP.NET MVC and Web API Tutorial