Asp.Net Web Api Service Lifetimes Transient Scoped Singleton Complete Guide

1. Singleton:

• Definition: A Singleton lifetime service is instantiated once per application's execution context, which typically means it lives as long as the application does.
• Use Case: Best suited for stateless services or those that have expensive initialization (database connections, complex configurations).
• Registration:

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddSingleton<IMyService, MyService>();
  }
  

• Important Info: Since the same instance is shared across all parts of your application, you need to be careful about modifying the state within Singleton services, as these changes are reflected application-wide.

2. Scoped:

• Definition: A Scoped lifetime service is created once per request and is available throughout the lifespan of that request.
• Use Case: Use for services that depend on or need to access data specific to a request but should not be reused across requests.
• Registration:

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddScoped<IMyScopedService, MyScopedService>();
  }
  

• Important Info: Scoped services are particularly useful for managing transactions within a request. Each request gets its own isolated instance of scoped services, reducing potential issues related to shared state and concurrency.

3. Transient:

• Definition: A Transient lifetime service is created every time it is requested from the services container.
• Use Case: Ideal for lightweight, short-lived services or those that are required multiple times within the same request.
• Registration:

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddTransient<IMyTransientService, MyTransientService>();
  }
  

• Important Info: Due to their creation each time they are requested, Transient services might be less efficient if many instances are required within a short period. However, they offer the greatest flexibility, making them suitable for disposable objects.

Choosing the Right Lifetime

Selecting the correct service lifetime depends on the behavior and requirements of your services:

• Performance Considerations: Transient services can be more resource-intensive due to frequent instantiation/destruction. Singletons, conversely, can optimize performance by reusing instances.
• State Management: Avoid sharing state between requests with Singletons. Scoped services provide safe state handling per request.
• Dependency Injection: Properly registering and injecting services based on their lifetimes is key to ensuring stability and reliability in your application.

Practical Example

Consider a simplified example where each service implements an interface IMyService:

public interface IMyService
{
    Guid Id { get; }
}

public class TransientService : IMyService
{
    public Guid Id { get; private set; }

    public TransientService()
    {
        Id = Guid.NewGuid();
    }
}

public class ScopedService : IMyService
{
    public Guid Id { get; private set; }

    public ScopedService()
    {
        Id = Guid.NewGuid();
    }
}

public class SingletonService : IMyService
{
    public Guid Id { get; private set; }

    public SingletonService()
    {
        Id = Guid.NewGuid();
    }
}

Registering these services:

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IMyService, TransientService>();
    services.AddScoped<IMyService, ScopedService>();
    services.AddSingleton<IMyService, SingletonService>();
}

Injecting and using within a controller:

[ApiController]
[Route("[controller]")]
public class TestController : ControllerBase
{
    private readonly IMyService _transientService;
    private readonly IMyService _scopedService;
    private readonly IMyService _singletonService;

    public TestController(IMyService transientService, IMyService scopedService, IMyService singletonService)
    {
        _transientService = transientService;
        _scopedService = scopedService;
        _singletonService = singletonService;
    }

    [HttpGet("test")]
    public IActionResult GetTest()
    {
        return Ok(new 
        {
            TransientId = _transientService.Id,
            ScopedId = _scopedService.Id,
            SingletonId = _singletonService.Id
        });
    }
}

Each service will provide different identifiers based on its lifetime when this endpoint is hit multiple times:

• Transient gives a new GUID each time.
• Scoped gives the same GUID within the same request but different GUIDs for distinct requests.
• Singleton always provides the same GUID.

Understanding these lifetimes will enable you to create robust and efficient web applications with ASP.NET Web API.

Keywords Related to the Topic:

1. Dependency Injection
2. Service Container
3. Lifetime Management
4. Request Scope
5. Application Life Cycle
6. Stateful Services
7. Stateless Services
8. Resource Optimization
9. Middleware
10. Startup Configuration