Dependency Injection Lifetimes

There are three service lifetimes when registering dependencies in .NET:

Lifetime	Method	Description
Singleton	AddSingleton<TInterface, TImpl>()	Single instance for the entire application lifetime. Shared by all requests.
Scoped	AddScoped<TInterface, TImpl>()	One instance per request (or scope). Shared within that request.
Transient	AddTransient<TInterface, TImpl>()	A new instance every time it is requested.

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1. Singleton Example

Registration:

builder.Services.AddSingleton<IGuidService, GuidService>();

Implementation:

public interface IGuidService
{
    Guid GetGuid();
}
 
public class GuidService : IGuidService
{
    private readonly Guid _guid;
 
    public GuidService()
    {
        _guid = Guid.NewGuid();
    }
 
    public Guid GetGuid() => _guid;
}

Usage in Controller:

public class HomeController : Controller
{
    private readonly IGuidService _guidService;
 
    public HomeController(IGuidService guidService)
    {
        _guidService = guidService;
    }
 
    public IActionResult Index()
    {
        var guid = _guidService.GetGuid(); // Same every time
        return Content($"Singleton GUID: {guid}");
    }
}

Result:

• Same Guid for every request, all users.

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2. Scoped Example

Registration:

builder.Services.AddScoped<IGuidService, GuidService>();

Same implementation as above.

Result:

• Same Guid within a single HTTP request, but different for each new request.

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3. Transient Example

Registration:

builder.Services.AddTransient<IGuidService, GuidService>();

Result:

• New GuidService instance every time it’s injected, even within the same request.

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🔍 Visual Difference (Optional Demo)

If you inject the same service twice in a controller, you can see the behavior clearly:

public class HomeController : Controller
{
    private readonly IGuidService _guidService1;
    private readonly IGuidService _guidService2;
 
    public HomeController(IGuidService guidService1, IGuidService guidService2)
    {
        _guidService1 = guidService1;
        _guidService2 = guidService2;
    }
 
    public IActionResult Index()
    {
        return Content($"1st: {_guidService1.GetGuid()} \n2nd: {_guidService2.GetGuid()}");
    }
}

Expected Behavior:

Lifetime	Result
Singleton	Both GUIDs are the same (shared globally).
Scoped	Same within request, changes between requests.
Transient	Different each time even in same request.

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Let me know if you’d like a diagram or sample project!