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नोट
This isn't the latest version of this article. For the current release, see the .NET 9 version of this article.
चेतावनी
This version of ASP.NET Core is no longer supported. For more information, see the .NET and .NET Core Support Policy. For the current release, see the .NET 9 version of this article.
महत्वपूर्ण
This information relates to a pre-release product that may be substantially modified before it's commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
For the current release, see the .NET 9 version of this article.
By Kirk Larkin, Steve Smith, and Brandon Dahler
ASP.NET Core supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies.
For Blazor DI guidance, which adds to or supersedes the guidance in this article, see ASP.NET Core Blazor dependency injection.
For information specific to dependency injection within MVC controllers, see Dependency injection into controllers in ASP.NET Core.
For information on using dependency injection in applications other than web apps, see Dependency injection in .NET.
For information on dependency injection of options, see Options pattern in ASP.NET Core.
This article provides information on dependency injection in ASP.NET Core. The primary documentation on using dependency injection is contained in Dependency injection in .NET.
View or download sample code (how to download)
A dependency is an object that another object depends on. Examine the following MyDependency
class with a WriteMessage
method that other classes depend on:
public class MyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage called. Message: {message}");
}
}
A class can create an instance of the MyDependency
class to make use of its WriteMessage
method. In the following example, the MyDependency
class is a dependency of the IndexModel
class:
public class IndexModel : PageModel
{
private readonly MyDependency _dependency = new MyDependency();
public void OnGet()
{
_dependency.WriteMessage("IndexModel.OnGet");
}
}
The class creates and directly depends on the MyDependency
class. Code dependencies, such as in the previous example, are problematic and should be avoided for the following reasons:
MyDependency
with a different implementation, the IndexModel
class must be modified.MyDependency
has dependencies, they must also be configured by the IndexModel
class. In a large project with multiple classes depending on MyDependency
, the configuration code becomes scattered across the app.Dependency injection addresses these problems through:
Program.cs
file.In the sample app, the IMyDependency
interface defines the WriteMessage
method:
public interface IMyDependency
{
void WriteMessage(string message);
}
This interface is implemented by a concrete type, MyDependency
:
public class MyDependency : IMyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage Message: {message}");
}
}
The sample app registers the IMyDependency
service with the concrete type MyDependency
. The AddScoped method registers the service with a scoped lifetime, the lifetime of a single request. Service lifetimes are described later in this article.
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
In the sample app, the IMyDependency
service is requested and used to call the WriteMessage
method:
public class Index2Model : PageModel
{
private readonly IMyDependency _myDependency;
public Index2Model(IMyDependency myDependency)
{
_myDependency = myDependency;
}
public void OnGet()
{
_myDependency.WriteMessage("Index2Model.OnGet");
}
}
By using the DI pattern, the controller or Razor Page:
MyDependency
, only the IMyDependency
interface it implements. That makes it easy to change the implementation without modifying the controller or Razor Page.MyDependency
, it's created by the DI container.The implementation of the IMyDependency
interface can be improved by using the built-in logging API:
public class MyDependency2 : IMyDependency
{
private readonly ILogger<MyDependency2> _logger;
public MyDependency2(ILogger<MyDependency2> logger)
{
_logger = logger;
}
public void WriteMessage(string message)
{
_logger.LogInformation( $"MyDependency2.WriteMessage Message: {message}");
}
}
The updated Program.cs
registers the new IMyDependency
implementation:
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency2>();
var app = builder.Build();
MyDependency2
depends on ILogger<TCategoryName>, which it requests in the constructor. ILogger<TCategoryName>
is a framework-provided service.
It's not unusual to use dependency injection in a chained fashion. Each requested dependency in turn requests its own dependencies. The container resolves the dependencies in the graph and returns the fully resolved service. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph.
The container resolves ILogger<TCategoryName>
by taking advantage of (generic) open types, eliminating the need to register every (generic) constructed type.
In dependency injection terminology, a service:
IMyDependency
service.The framework provides a robust logging system. The IMyDependency
implementations shown in the preceding examples were written to demonstrate basic DI, not to implement logging. Most apps shouldn't need to write loggers. The following code demonstrates using the default logging, which doesn't require any services to be registered:
public class AboutModel : PageModel
{
private readonly ILogger _logger;
public AboutModel(ILogger<AboutModel> logger)
{
_logger = logger;
}
public string Message { get; set; } = string.Empty;
public void OnGet()
{
Message = $"About page visited at {DateTime.UtcNow.ToLongTimeString()}";
_logger.LogInformation(Message);
}
}
The preceding code works correctly without changing anything in Program.cs
, because logging is provided by the framework.
The ASP.NET Core framework uses a convention for registering a group of related services. The convention is to use a single Add{GROUP_NAME}
extension method to register all of the services required by a framework feature. For example, the AddControllers extension method registers the services required for MVC controllers.
The following code is generated by the Razor Pages template using individual user accounts and shows how to add additional services to the container using the extension methods AddDbContext and AddDefaultIdentity:
using DependencyInjectionSample.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();
builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
.AddEntityFrameworkStores<ApplicationDbContext>();
builder.Services.AddRazorPages();
var app = builder.Build();
Consider the following which registers services and configures options:
using ConfigSample.Options;
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.Configure<PositionOptions>(
builder.Configuration.GetSection(PositionOptions.Position));
builder.Services.Configure<ColorOptions>(
builder.Configuration.GetSection(ColorOptions.Color));
builder.Services.AddScoped<IMyDependency, MyDependency>();
builder.Services.AddScoped<IMyDependency2, MyDependency2>();
var app = builder.Build();
Related groups of registrations can be moved to an extension method to register services. For example, the configuration services are added to the following class:
using ConfigSample.Options;
using Microsoft.Extensions.Configuration;
namespace Microsoft.Extensions.DependencyInjection
{
public static class MyConfigServiceCollectionExtensions
{
public static IServiceCollection AddConfig(
this IServiceCollection services, IConfiguration config)
{
services.Configure<PositionOptions>(
config.GetSection(PositionOptions.Position));
services.Configure<ColorOptions>(
config.GetSection(ColorOptions.Color));
return services;
}
public static IServiceCollection AddMyDependencyGroup(
this IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency>();
services.AddScoped<IMyDependency2, MyDependency2>();
return services;
}
}
}
The remaining services are registered in a similar class. The following code uses the new extension methods to register the services:
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services
.AddConfig(builder.Configuration)
.AddMyDependencyGroup();
builder.Services.AddRazorPages();
var app = builder.Build();
Note: Each services.Add{GROUP_NAME}
extension method adds and potentially configures services. For example, AddControllersWithViews adds the services MVC controllers with views require, and AddRazorPages adds the services Razor Pages requires.
See Service lifetimes in Dependency injection in .NET
To use scoped services in middleware, use one of the following approaches:
Invoke
or InvokeAsync
method. Using constructor injection throws a runtime exception because it forces the scoped service to behave like a singleton. The sample in the Lifetime and registration options section demonstrates the InvokeAsync
approach.For more information, see Write custom ASP.NET Core middleware.
See Service registration methods in Dependency injection in .NET
It's common to use multiple implementations when mocking types for testing.
Registering a service with only an implementation type is equivalent to registering that service with the same implementation and service type. This is why multiple implementations of a service can't be registered using the methods that don't take an explicit service type. These methods can register multiple instances of a service, but they all have the same implementation type.
Any of these service registration methods can be used to register multiple service instances of the same service type. In the following example, AddSingleton
is called twice with IMyDependency
as the service type. The second call to AddSingleton
overrides the previous one when resolved as IMyDependency
and adds to the previous one when multiple services are resolved via IEnumerable<IMyDependency>
. Services appear in the order they were registered when resolved via IEnumerable<{SERVICE}>
.
services.AddSingleton<IMyDependency, MyDependency>();
services.AddSingleton<IMyDependency, DifferentDependency>();
public class MyService
{
public MyService(IMyDependency myDependency,
IEnumerable<IMyDependency> myDependencies)
{
Trace.Assert(myDependency is DifferentDependency);
var dependencyArray = myDependencies.ToArray();
Trace.Assert(dependencyArray[0] is MyDependency);
Trace.Assert(dependencyArray[1] is DifferentDependency);
}
}
The term keyed services refers to a mechanism for registering and retrieving Dependency Injection (DI) services using keys. A service is associated with a key by calling AddKeyedSingleton (or AddKeyedScoped
or AddKeyedTransient
) to register it. Access a registered service by specifying the key with the [FromKeyedServices]
attribute. The following code shows how to use keyed services:
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddKeyedSingleton<ICache, BigCache>("big");
builder.Services.AddKeyedSingleton<ICache, SmallCache>("small");
builder.Services.AddControllers();
var app = builder.Build();
app.MapGet("/big", ([FromKeyedServices("big")] ICache bigCache) => bigCache.Get("date"));
app.MapGet("/small", ([FromKeyedServices("small")] ICache smallCache) =>
smallCache.Get("date"));
app.MapControllers();
app.Run();
public interface ICache
{
object Get(string key);
}
public class BigCache : ICache
{
public object Get(string key) => $"Resolving {key} from big cache.";
}
public class SmallCache : ICache
{
public object Get(string key) => $"Resolving {key} from small cache.";
}
[ApiController]
[Route("/cache")]
public class CustomServicesApiController : Controller
{
[HttpGet("big-cache")]
public ActionResult<object> GetOk([FromKeyedServices("big")] ICache cache)
{
return cache.Get("data-mvc");
}
}
public class MyHub : Hub
{
public void Method([FromKeyedServices("small")] ICache cache)
{
Console.WriteLine(cache.Get("signalr"));
}
}
Middleware supports Keyed services in both the constructor and the Invoke
/InvokeAsync
method:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddKeyedSingleton<MySingletonClass>("test");
builder.Services.AddKeyedScoped<MyScopedClass>("test2");
var app = builder.Build();
app.UseMiddleware<MyMiddleware>();
app.Run();
internal class MyMiddleware
{
private readonly RequestDelegate _next;
public MyMiddleware(RequestDelegate next,
[FromKeyedServices("test")] MySingletonClass service)
{
_next = next;
}
public Task Invoke(HttpContext context,
[FromKeyedServices("test2")]
MyScopedClass scopedService) => _next(context);
}
For more information on creating Middleware, see Write custom ASP.NET Core middleware
See Constructor injection behavior in Dependency injection in .NET
By default, Entity Framework contexts are added to the service container using the scoped lifetime because web app database operations are normally scoped to the client request. To use a different lifetime, specify the lifetime by using an AddDbContext overload. Services of a given lifetime shouldn't use a database context with a lifetime that's shorter than the service's lifetime.
To demonstrate the difference between service lifetimes and their registration options, consider the following interfaces that represent a task as an operation with an identifier, OperationId
. Depending on how the lifetime of an operation's service is configured for the following interfaces, the container provides either the same or different instances of the service when requested by a class:
public interface IOperation
{
string OperationId { get; }
}
public interface IOperationTransient : IOperation { }
public interface IOperationScoped : IOperation { }
public interface IOperationSingleton : IOperation { }
The following Operation
class implements all of the preceding interfaces. The Operation
constructor generates a GUID and stores the last 4 characters in the OperationId
property:
public class Operation : IOperationTransient, IOperationScoped, IOperationSingleton
{
public Operation()
{
OperationId = Guid.NewGuid().ToString()[^4..];
}
public string OperationId { get; }
}
The following code creates multiple registrations of the Operation
class according to the named lifetimes:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddTransient<IOperationTransient, Operation>();
builder.Services.AddScoped<IOperationScoped, Operation>();
builder.Services.AddSingleton<IOperationSingleton, Operation>();
var app = builder.Build();
if (!app.Environment.IsDevelopment())
{
app.UseExceptionHandler("/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseMyMiddleware();
app.UseRouting();
app.UseAuthorization();
app.MapRazorPages();
app.Run();
The sample app demonstrates object lifetimes both within and between requests. The IndexModel
and the middleware request each kind of IOperation
type and log the OperationId
for each:
public class IndexModel : PageModel
{
private readonly ILogger _logger;
private readonly IOperationTransient _transientOperation;
private readonly IOperationSingleton _singletonOperation;
private readonly IOperationScoped _scopedOperation;
public IndexModel(ILogger<IndexModel> logger,
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation)
{
_logger = logger;
_transientOperation = transientOperation;
_scopedOperation = scopedOperation;
_singletonOperation = singletonOperation;
}
public void OnGet()
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + _scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
}
}
Similar to the IndexModel
, the middleware resolves the same services:
public class MyMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger _logger;
private readonly IOperationSingleton _singletonOperation;
public MyMiddleware(RequestDelegate next, ILogger<MyMiddleware> logger,
IOperationSingleton singletonOperation)
{
_logger = logger;
_singletonOperation = singletonOperation;
_next = next;
}
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
}
public static class MyMiddlewareExtensions
{
public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<MyMiddleware>();
}
}
Scoped and transient services must be resolved in the InvokeAsync
method:
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
The logger output shows:
OperationId
value is different in the IndexModel
and in the middleware.To reduce the logging output, set "Logging:LogLevel:Microsoft:Error" in the appsettings.Development.json
file:
{
"MyKey": "MyKey from appsettings.Developement.json",
"Logging": {
"LogLevel": {
"Default": "Information",
"System": "Debug",
"Microsoft": "Error"
}
}
}
The following code shows how to resolve a scoped service for a limited duration when the app starts:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
using (var serviceScope = app.Services.CreateScope())
{
var services = serviceScope.ServiceProvider;
var myDependency = services.GetRequiredService<IMyDependency>();
myDependency.WriteMessage("Call services from main");
}
app.MapGet("/", () => "Hello World!");
app.Run();
See Constructor injection behavior in Dependency injection in .NET
For more information, see Scope validation.
Services and their dependencies within an ASP.NET Core request are exposed through HttpContext.RequestServices.
The framework creates a scope per request, and RequestServices
exposes the scoped service provider. All scoped services are valid for as long as the request is active.
नोट
Prefer requesting dependencies as constructor parameters over resolving services from RequestServices
. Requesting dependencies as constructor parameters yields classes that are easier to test.
When designing services for dependency injection:
If a class has many injected dependencies, it might be a sign that the class has too many responsibilities and violates the Single Responsibility Principle (SRP). Attempt to refactor the class by moving some of its responsibilities into new classes. Keep in mind that Razor Pages page model classes and MVC controller classes should focus on UI concerns.
The container calls Dispose for the IDisposable types it creates. Services resolved from the container should never be disposed by the developer. If a type or factory is registered as a singleton, the container disposes the singleton automatically.
In the following example, the services are created by the service container and disposed automatically:
public class Service1 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service1: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service1.Dispose");
_disposed = true;
}
}
public class Service2 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service2: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service2.Dispose");
_disposed = true;
}
}
public interface IService3
{
public void Write(string message);
}
public class Service3 : IService3, IDisposable
{
private bool _disposed;
public Service3(string myKey)
{
MyKey = myKey;
}
public string MyKey { get; }
public void Write(string message)
{
Console.WriteLine($"Service3: {message}, MyKey = {MyKey}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service3.Dispose");
_disposed = true;
}
}
using DIsample2.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<Service1>();
builder.Services.AddSingleton<Service2>();
var myKey = builder.Configuration["MyKey"];
builder.Services.AddSingleton<IService3>(sp => new Service3(myKey));
var app = builder.Build();
public class IndexModel : PageModel
{
private readonly Service1 _service1;
private readonly Service2 _service2;
private readonly IService3 _service3;
public IndexModel(Service1 service1, Service2 service2, IService3 service3)
{
_service1 = service1;
_service2 = service2;
_service3 = service3;
}
public void OnGet()
{
_service1.Write("IndexModel.OnGet");
_service2.Write("IndexModel.OnGet");
_service3.Write("IndexModel.OnGet");
}
}
The debug console shows the following output after each refresh of the Index page:
Service1: IndexModel.OnGet
Service2: IndexModel.OnGet
Service3: IndexModel.OnGet, MyKey = MyKey from appsettings.Developement.json
Service1.Dispose
Consider the following code:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddSingleton(new Service1());
builder.Services.AddSingleton(new Service2());
In the preceding code:
See IDisposable guidance for Transient and shared instance in Dependency injection in .NET
See Default service container replacement in Dependency injection in .NET
See Recommendations in Dependency injection in .NET
Avoid using the service locator pattern. For example, don't invoke GetService to obtain a service instance when you can use DI instead:
Incorrect:
Correct:
public class MyClass
{
private readonly IOptionsMonitor<MyOptions> _optionsMonitor;
public MyClass(IOptionsMonitor<MyOptions> optionsMonitor)
{
_optionsMonitor = optionsMonitor;
}
public void MyMethod()
{
var option = _optionsMonitor.CurrentValue.Option;
...
}
}
Another service locator variation to avoid is injecting a factory that resolves dependencies at runtime. Both of these practices mix Inversion of Control strategies.
Avoid static access to HttpContext
(for example, IHttpContextAccessor.HttpContext).
DI is an alternative to static/global object access patterns. You might not be able to realize the benefits of DI if you mix it with static object access.
Orchard Core is an application framework for building modular, multitenant applications on ASP.NET Core. For more information, see the Orchard Core Documentation.
See the Orchard Core samples for examples of how to build modular and multi-tenant apps using just the Orchard Core Framework without any of its CMS-specific features.
Program.cs
registers services that the app uses, including platform features, such as Entity Framework Core and ASP.NET Core MVC. Initially, the IServiceCollection
provided to Program.cs
has services defined by the framework depending on how the host was configured. For apps based on the ASP.NET Core templates, the framework registers more than 250 services.
The following table lists a small sample of these framework-registered services:
Service Type | Lifetime |
---|---|
Microsoft.AspNetCore.Hosting.Builder.IApplicationBuilderFactory | Transient |
IHostApplicationLifetime | Singleton |
IWebHostEnvironment | Singleton |
Microsoft.AspNetCore.Hosting.IStartup | Singleton |
Microsoft.AspNetCore.Hosting.IStartupFilter | Transient |
Microsoft.AspNetCore.Hosting.Server.IServer | Singleton |
Microsoft.AspNetCore.Http.IHttpContextFactory | Transient |
Microsoft.Extensions.Logging.ILogger<TCategoryName> | Singleton |
Microsoft.Extensions.Logging.ILoggerFactory | Singleton |
Microsoft.Extensions.ObjectPool.ObjectPoolProvider | Singleton |
Microsoft.Extensions.Options.IConfigureOptions<TOptions> | Transient |
Microsoft.Extensions.Options.IOptions<TOptions> | Singleton |
System.Diagnostics.DiagnosticSource | Singleton |
System.Diagnostics.DiagnosticListener | Singleton |
By Kirk Larkin, Steve Smith, and Brandon Dahler
ASP.NET Core supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies.
For more information specific to dependency injection within MVC controllers, see Dependency injection into controllers in ASP.NET Core.
For information on using dependency injection in applications other than web apps, see Dependency injection in .NET.
For more information on dependency injection of options, see Options pattern in ASP.NET Core.
This topic provides information on dependency injection in ASP.NET Core. The primary documentation on using dependency injection is contained in Dependency injection in .NET.
View or download sample code (how to download)
A dependency is an object that another object depends on. Examine the following MyDependency
class with a WriteMessage
method that other classes depend on:
public class MyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage called. Message: {message}");
}
}
A class can create an instance of the MyDependency
class to make use of its WriteMessage
method. In the following example, the MyDependency
class is a dependency of the IndexModel
class:
public class IndexModel : PageModel
{
private readonly MyDependency _dependency = new MyDependency();
public void OnGet()
{
_dependency.WriteMessage("IndexModel.OnGet");
}
}
The class creates and directly depends on the MyDependency
class. Code dependencies, such as in the previous example, are problematic and should be avoided for the following reasons:
MyDependency
with a different implementation, the IndexModel
class must be modified.MyDependency
has dependencies, they must also be configured by the IndexModel
class. In a large project with multiple classes depending on MyDependency
, the configuration code becomes scattered across the app.Dependency injection addresses these problems through:
Program.cs
file.In the sample app, the IMyDependency
interface defines the WriteMessage
method:
public interface IMyDependency
{
void WriteMessage(string message);
}
This interface is implemented by a concrete type, MyDependency
:
public class MyDependency : IMyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage Message: {message}");
}
}
The sample app registers the IMyDependency
service with the concrete type MyDependency
. The AddScoped method registers the service with a scoped lifetime, the lifetime of a single request. Service lifetimes are described later in this topic.
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
In the sample app, the IMyDependency
service is requested and used to call the WriteMessage
method:
public class Index2Model : PageModel
{
private readonly IMyDependency _myDependency;
public Index2Model(IMyDependency myDependency)
{
_myDependency = myDependency;
}
public void OnGet()
{
_myDependency.WriteMessage("Index2Model.OnGet");
}
}
By using the DI pattern, the controller or Razor Page:
MyDependency
, only the IMyDependency
interface it implements. That makes it easy to change the implementation without modifying the controller or Razor Page.MyDependency
, it's created by the DI container.The implementation of the IMyDependency
interface can be improved by using the built-in logging API:
public class MyDependency2 : IMyDependency
{
private readonly ILogger<MyDependency2> _logger;
public MyDependency2(ILogger<MyDependency2> logger)
{
_logger = logger;
}
public void WriteMessage(string message)
{
_logger.LogInformation( $"MyDependency2.WriteMessage Message: {message}");
}
}
The updated Program.cs
registers the new IMyDependency
implementation:
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency2>();
var app = builder.Build();
MyDependency2
depends on ILogger<TCategoryName>, which it requests in the constructor. ILogger<TCategoryName>
is a framework-provided service.
It's not unusual to use dependency injection in a chained fashion. Each requested dependency in turn requests its own dependencies. The container resolves the dependencies in the graph and returns the fully resolved service. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph.
The container resolves ILogger<TCategoryName>
by taking advantage of (generic) open types, eliminating the need to register every (generic) constructed type.
In dependency injection terminology, a service:
IMyDependency
service.The framework provides a robust logging system. The IMyDependency
implementations shown in the preceding examples were written to demonstrate basic DI, not to implement logging. Most apps shouldn't need to write loggers. The following code demonstrates using the default logging, which doesn't require any services to be registered:
public class AboutModel : PageModel
{
private readonly ILogger _logger;
public AboutModel(ILogger<AboutModel> logger)
{
_logger = logger;
}
public string Message { get; set; } = string.Empty;
public void OnGet()
{
Message = $"About page visited at {DateTime.UtcNow.ToLongTimeString()}";
_logger.LogInformation(Message);
}
}
Using the preceding code, there is no need to update Program.cs
, because logging is provided by the framework.
The ASP.NET Core framework uses a convention for registering a group of related services. The convention is to use a single Add{GROUP_NAME}
extension method to register all of the services required by a framework feature. For example, the AddControllers extension method registers the services required for MVC controllers.
The following code is generated by the Razor Pages template using individual user accounts and shows how to add additional services to the container using the extension methods AddDbContext and AddDefaultIdentity:
using DependencyInjectionSample.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();
builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
.AddEntityFrameworkStores<ApplicationDbContext>();
builder.Services.AddRazorPages();
var app = builder.Build();
Consider the following which registers services and configures options:
using ConfigSample.Options;
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.Configure<PositionOptions>(
builder.Configuration.GetSection(PositionOptions.Position));
builder.Services.Configure<ColorOptions>(
builder.Configuration.GetSection(ColorOptions.Color));
builder.Services.AddScoped<IMyDependency, MyDependency>();
builder.Services.AddScoped<IMyDependency2, MyDependency2>();
var app = builder.Build();
Related groups of registrations can be moved to an extension method to register services. For example, the configuration services are added to the following class:
using ConfigSample.Options;
using Microsoft.Extensions.Configuration;
namespace Microsoft.Extensions.DependencyInjection
{
public static class MyConfigServiceCollectionExtensions
{
public static IServiceCollection AddConfig(
this IServiceCollection services, IConfiguration config)
{
services.Configure<PositionOptions>(
config.GetSection(PositionOptions.Position));
services.Configure<ColorOptions>(
config.GetSection(ColorOptions.Color));
return services;
}
public static IServiceCollection AddMyDependencyGroup(
this IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency>();
services.AddScoped<IMyDependency2, MyDependency2>();
return services;
}
}
}
The remaining services are registered in a similar class. The following code uses the new extension methods to register the services:
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services
.AddConfig(builder.Configuration)
.AddMyDependencyGroup();
builder.Services.AddRazorPages();
var app = builder.Build();
Note: Each services.Add{GROUP_NAME}
extension method adds and potentially configures services. For example, AddControllersWithViews adds the services MVC controllers with views require, and AddRazorPages adds the services Razor Pages requires.
See Service lifetimes in Dependency injection in .NET
To use scoped services in middleware, use one of the following approaches:
Invoke
or InvokeAsync
method. Using constructor injection throws a runtime exception because it forces the scoped service to behave like a singleton. The sample in the Lifetime and registration options section demonstrates the InvokeAsync
approach.For more information, see Write custom ASP.NET Core middleware.
See Service registration methods in Dependency injection in .NET
It's common to use multiple implementations when mocking types for testing.
Registering a service with only an implementation type is equivalent to registering that service with the same implementation and service type. This is why multiple implementations of a service cannot be registered using the methods that don't take an explicit service type. These methods can register multiple instances of a service, but they will all have the same implementation type.
Any of the above service registration methods can be used to register multiple service instances of the same service type. In the following example, AddSingleton
is called twice with IMyDependency
as the service type. The second call to AddSingleton
overrides the previous one when resolved as IMyDependency
and adds to the previous one when multiple services are resolved via IEnumerable<IMyDependency>
. Services appear in the order they were registered when resolved via IEnumerable<{SERVICE}>
.
services.AddSingleton<IMyDependency, MyDependency>();
services.AddSingleton<IMyDependency, DifferentDependency>();
public class MyService
{
public MyService(IMyDependency myDependency,
IEnumerable<IMyDependency> myDependencies)
{
Trace.Assert(myDependency is DifferentDependency);
var dependencyArray = myDependencies.ToArray();
Trace.Assert(dependencyArray[0] is MyDependency);
Trace.Assert(dependencyArray[1] is DifferentDependency);
}
}
Keyed services refers to a mechanism for registering and retrieving Dependency Injection (DI) services using keys. A service is associated with a key by calling AddKeyedSingleton (or AddKeyedScoped
or AddKeyedTransient
) to register it. Access a registered service by specifying the key with the [FromKeyedServices]
attribute. The following code shows how to use keyed services:
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddKeyedSingleton<ICache, BigCache>("big");
builder.Services.AddKeyedSingleton<ICache, SmallCache>("small");
builder.Services.AddControllers();
var app = builder.Build();
app.MapGet("/big", ([FromKeyedServices("big")] ICache bigCache) => bigCache.Get("date"));
app.MapGet("/small", ([FromKeyedServices("small")] ICache smallCache) =>
smallCache.Get("date"));
app.MapControllers();
app.Run();
public interface ICache
{
object Get(string key);
}
public class BigCache : ICache
{
public object Get(string key) => $"Resolving {key} from big cache.";
}
public class SmallCache : ICache
{
public object Get(string key) => $"Resolving {key} from small cache.";
}
[ApiController]
[Route("/cache")]
public class CustomServicesApiController : Controller
{
[HttpGet("big-cache")]
public ActionResult<object> GetOk([FromKeyedServices("big")] ICache cache)
{
return cache.Get("data-mvc");
}
}
public class MyHub : Hub
{
public void Method([FromKeyedServices("small")] ICache cache)
{
Console.WriteLine(cache.Get("signalr"));
}
}
See Constructor injection behavior in Dependency injection in .NET
By default, Entity Framework contexts are added to the service container using the scoped lifetime because web app database operations are normally scoped to the client request. To use a different lifetime, specify the lifetime by using an AddDbContext overload. Services of a given lifetime shouldn't use a database context with a lifetime that's shorter than the service's lifetime.
To demonstrate the difference between service lifetimes and their registration options, consider the following interfaces that represent a task as an operation with an identifier, OperationId
. Depending on how the lifetime of an operation's service is configured for the following interfaces, the container provides either the same or different instances of the service when requested by a class:
public interface IOperation
{
string OperationId { get; }
}
public interface IOperationTransient : IOperation { }
public interface IOperationScoped : IOperation { }
public interface IOperationSingleton : IOperation { }
The following Operation
class implements all of the preceding interfaces. The Operation
constructor generates a GUID and stores the last 4 characters in the OperationId
property:
public class Operation : IOperationTransient, IOperationScoped, IOperationSingleton
{
public Operation()
{
OperationId = Guid.NewGuid().ToString()[^4..];
}
public string OperationId { get; }
}
The following code creates multiple registrations of the Operation
class according to the named lifetimes:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddTransient<IOperationTransient, Operation>();
builder.Services.AddScoped<IOperationScoped, Operation>();
builder.Services.AddSingleton<IOperationSingleton, Operation>();
var app = builder.Build();
if (!app.Environment.IsDevelopment())
{
app.UseExceptionHandler("/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseMyMiddleware();
app.UseRouting();
app.UseAuthorization();
app.MapRazorPages();
app.Run();
The sample app demonstrates object lifetimes both within and between requests. The IndexModel
and the middleware request each kind of IOperation
type and log the OperationId
for each:
public class IndexModel : PageModel
{
private readonly ILogger _logger;
private readonly IOperationTransient _transientOperation;
private readonly IOperationSingleton _singletonOperation;
private readonly IOperationScoped _scopedOperation;
public IndexModel(ILogger<IndexModel> logger,
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation)
{
_logger = logger;
_transientOperation = transientOperation;
_scopedOperation = scopedOperation;
_singletonOperation = singletonOperation;
}
public void OnGet()
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + _scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
}
}
Similar to the IndexModel
, the middleware resolves the same services:
public class MyMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger _logger;
private readonly IOperationSingleton _singletonOperation;
public MyMiddleware(RequestDelegate next, ILogger<MyMiddleware> logger,
IOperationSingleton singletonOperation)
{
_logger = logger;
_singletonOperation = singletonOperation;
_next = next;
}
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
}
public static class MyMiddlewareExtensions
{
public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<MyMiddleware>();
}
}
Scoped and transient services must be resolved in the InvokeAsync
method:
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
The logger output shows:
OperationId
value is different in the IndexModel
and in the middleware.To reduce the logging output, set "Logging:LogLevel:Microsoft:Error" in the appsettings.Development.json
file:
{
"MyKey": "MyKey from appsettings.Developement.json",
"Logging": {
"LogLevel": {
"Default": "Information",
"System": "Debug",
"Microsoft": "Error"
}
}
}
The following code shows how to resolve a scoped service for a limited duration when the app starts:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
using (var serviceScope = app.Services.CreateScope())
{
var services = serviceScope.ServiceProvider;
var myDependency = services.GetRequiredService<IMyDependency>();
myDependency.WriteMessage("Call services from main");
}
app.MapGet("/", () => "Hello World!");
app.Run();
See Constructor injection behavior in Dependency injection in .NET
For more information, see Scope validation.
Services and their dependencies within an ASP.NET Core request are exposed through HttpContext.RequestServices.
The framework creates a scope per request, and RequestServices
exposes the scoped service provider. All scoped services are valid for as long as the request is active.
नोट
Prefer requesting dependencies as constructor parameters over resolving services from RequestServices
. Requesting dependencies as constructor parameters yields classes that are easier to test.
When designing services for dependency injection:
If a class has a lot of injected dependencies, it might be a sign that the class has too many responsibilities and violates the Single Responsibility Principle (SRP). Attempt to refactor the class by moving some of its responsibilities into new classes. Keep in mind that Razor Pages page model classes and MVC controller classes should focus on UI concerns.
The container calls Dispose for the IDisposable types it creates. Services resolved from the container should never be disposed by the developer. If a type or factory is registered as a singleton, the container disposes the singleton automatically.
In the following example, the services are created by the service container and disposed automatically: dependency-injection\samples\6.x\DIsample2\DIsample2\Services\Service1.cs
public class Service1 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service1: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service1.Dispose");
_disposed = true;
}
}
public class Service2 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service2: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service2.Dispose");
_disposed = true;
}
}
public interface IService3
{
public void Write(string message);
}
public class Service3 : IService3, IDisposable
{
private bool _disposed;
public Service3(string myKey)
{
MyKey = myKey;
}
public string MyKey { get; }
public void Write(string message)
{
Console.WriteLine($"Service3: {message}, MyKey = {MyKey}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service3.Dispose");
_disposed = true;
}
}
using DIsample2.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<Service1>();
builder.Services.AddSingleton<Service2>();
var myKey = builder.Configuration["MyKey"];
builder.Services.AddSingleton<IService3>(sp => new Service3(myKey));
var app = builder.Build();
public class IndexModel : PageModel
{
private readonly Service1 _service1;
private readonly Service2 _service2;
private readonly IService3 _service3;
public IndexModel(Service1 service1, Service2 service2, IService3 service3)
{
_service1 = service1;
_service2 = service2;
_service3 = service3;
}
public void OnGet()
{
_service1.Write("IndexModel.OnGet");
_service2.Write("IndexModel.OnGet");
_service3.Write("IndexModel.OnGet");
}
}
The debug console shows the following output after each refresh of the Index page:
Service1: IndexModel.OnGet
Service2: IndexModel.OnGet
Service3: IndexModel.OnGet, MyKey = MyKey from appsettings.Developement.json
Service1.Dispose
Consider the following code:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddSingleton(new Service1());
builder.Services.AddSingleton(new Service2());
In the preceding code:
See IDisposable guidance for Transient and shared instance in Dependency injection in .NET
See Default service container replacement in Dependency injection in .NET
See Recommendations in Dependency injection in .NET
Avoid using the service locator pattern. For example, don't invoke GetService to obtain a service instance when you can use DI instead:
Incorrect:
Correct:
public class MyClass
{
private readonly IOptionsMonitor<MyOptions> _optionsMonitor;
public MyClass(IOptionsMonitor<MyOptions> optionsMonitor)
{
_optionsMonitor = optionsMonitor;
}
public void MyMethod()
{
var option = _optionsMonitor.CurrentValue.Option;
...
}
}
Another service locator variation to avoid is injecting a factory that resolves dependencies at runtime. Both of these practices mix Inversion of Control strategies.
Avoid static access to HttpContext
(for example, IHttpContextAccessor.HttpContext).
DI is an alternative to static/global object access patterns. You may not be able to realize the benefits of DI if you mix it with static object access.
Orchard Core is an application framework for building modular, multi-tenant applications on ASP.NET Core. For more information, see the Orchard Core Documentation.
See the Orchard Core samples for examples of how to build modular and multi-tenant apps using just the Orchard Core Framework without any of its CMS-specific features.
Program.cs
registers services that the app uses, including platform features, such as Entity Framework Core and ASP.NET Core MVC. Initially, the IServiceCollection
provided to Program.cs
has services defined by the framework depending on how the host was configured. For apps based on the ASP.NET Core templates, the framework registers more than 250 services.
The following table lists a small sample of these framework-registered services:
Service Type | Lifetime |
---|---|
Microsoft.AspNetCore.Hosting.Builder.IApplicationBuilderFactory | Transient |
IHostApplicationLifetime | Singleton |
IWebHostEnvironment | Singleton |
Microsoft.AspNetCore.Hosting.IStartup | Singleton |
Microsoft.AspNetCore.Hosting.IStartupFilter | Transient |
Microsoft.AspNetCore.Hosting.Server.IServer | Singleton |
Microsoft.AspNetCore.Http.IHttpContextFactory | Transient |
Microsoft.Extensions.Logging.ILogger<TCategoryName> | Singleton |
Microsoft.Extensions.Logging.ILoggerFactory | Singleton |
Microsoft.Extensions.ObjectPool.ObjectPoolProvider | Singleton |
Microsoft.Extensions.Options.IConfigureOptions<TOptions> | Transient |
Microsoft.Extensions.Options.IOptions<TOptions> | Singleton |
System.Diagnostics.DiagnosticSource | Singleton |
System.Diagnostics.DiagnosticListener | Singleton |
By Kirk Larkin, Steve Smith, and Brandon Dahler
ASP.NET Core supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies.
For more information specific to dependency injection within MVC controllers, see Dependency injection into controllers in ASP.NET Core.
For information on using dependency injection in applications other than web apps, see Dependency injection in .NET.
For more information on dependency injection of options, see Options pattern in ASP.NET Core.
This topic provides information on dependency injection in ASP.NET Core. The primary documentation on using dependency injection is contained in Dependency injection in .NET.
View or download sample code (how to download)
A dependency is an object that another object depends on. Examine the following MyDependency
class with a WriteMessage
method that other classes depend on:
public class MyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage called. Message: {message}");
}
}
A class can create an instance of the MyDependency
class to make use of its WriteMessage
method. In the following example, the MyDependency
class is a dependency of the IndexModel
class:
public class IndexModel : PageModel
{
private readonly MyDependency _dependency = new MyDependency();
public void OnGet()
{
_dependency.WriteMessage("IndexModel.OnGet");
}
}
The class creates and directly depends on the MyDependency
class. Code dependencies, such as in the previous example, are problematic and should be avoided for the following reasons:
MyDependency
with a different implementation, the IndexModel
class must be modified.MyDependency
has dependencies, they must also be configured by the IndexModel
class. In a large project with multiple classes depending on MyDependency
, the configuration code becomes scattered across the app.Dependency injection addresses these problems through:
Program.cs
file.In the sample app, the IMyDependency
interface defines the WriteMessage
method:
public interface IMyDependency
{
void WriteMessage(string message);
}
This interface is implemented by a concrete type, MyDependency
:
public class MyDependency : IMyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage Message: {message}");
}
}
The sample app registers the IMyDependency
service with the concrete type MyDependency
. The AddScoped method registers the service with a scoped lifetime, the lifetime of a single request. Service lifetimes are described later in this topic.
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
In the sample app, the IMyDependency
service is requested and used to call the WriteMessage
method:
public class Index2Model : PageModel
{
private readonly IMyDependency _myDependency;
public Index2Model(IMyDependency myDependency)
{
_myDependency = myDependency;
}
public void OnGet()
{
_myDependency.WriteMessage("Index2Model.OnGet");
}
}
By using the DI pattern, the controller or Razor Page:
MyDependency
, only the IMyDependency
interface it implements. That makes it easy to change the implementation without modifying the controller or Razor Page.MyDependency
, it's created by the DI container.The implementation of the IMyDependency
interface can be improved by using the built-in logging API:
public class MyDependency2 : IMyDependency
{
private readonly ILogger<MyDependency2> _logger;
public MyDependency2(ILogger<MyDependency2> logger)
{
_logger = logger;
}
public void WriteMessage(string message)
{
_logger.LogInformation( $"MyDependency2.WriteMessage Message: {message}");
}
}
The updated Program.cs
registers the new IMyDependency
implementation:
using DependencyInjectionSample.Interfaces;
using DependencyInjectionSample.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<IMyDependency, MyDependency2>();
var app = builder.Build();
MyDependency2
depends on ILogger<TCategoryName>, which it requests in the constructor. ILogger<TCategoryName>
is a framework-provided service.
It's not unusual to use dependency injection in a chained fashion. Each requested dependency in turn requests its own dependencies. The container resolves the dependencies in the graph and returns the fully resolved service. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph.
The container resolves ILogger<TCategoryName>
by taking advantage of (generic) open types, eliminating the need to register every (generic) constructed type.
In dependency injection terminology, a service:
IMyDependency
service.The framework provides a robust logging system. The IMyDependency
implementations shown in the preceding examples were written to demonstrate basic DI, not to implement logging. Most apps shouldn't need to write loggers. The following code demonstrates using the default logging, which doesn't require any services to be registered:
public class AboutModel : PageModel
{
private readonly ILogger _logger;
public AboutModel(ILogger<AboutModel> logger)
{
_logger = logger;
}
public string Message { get; set; } = string.Empty;
public void OnGet()
{
Message = $"About page visited at {DateTime.UtcNow.ToLongTimeString()}";
_logger.LogInformation(Message);
}
}
Using the preceding code, there is no need to update Program.cs
, because logging is provided by the framework.
The ASP.NET Core framework uses a convention for registering a group of related services. The convention is to use a single Add{GROUP_NAME}
extension method to register all of the services required by a framework feature. For example, the AddControllers extension method registers the services required for MVC controllers.
The following code is generated by the Razor Pages template using individual user accounts and shows how to add additional services to the container using the extension methods AddDbContext and AddDefaultIdentity:
using DependencyInjectionSample.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
var builder = WebApplication.CreateBuilder(args);
var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();
builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
.AddEntityFrameworkStores<ApplicationDbContext>();
builder.Services.AddRazorPages();
var app = builder.Build();
Consider the following which registers services and configures options:
using ConfigSample.Options;
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.Configure<PositionOptions>(
builder.Configuration.GetSection(PositionOptions.Position));
builder.Services.Configure<ColorOptions>(
builder.Configuration.GetSection(ColorOptions.Color));
builder.Services.AddScoped<IMyDependency, MyDependency>();
builder.Services.AddScoped<IMyDependency2, MyDependency2>();
var app = builder.Build();
Related groups of registrations can be moved to an extension method to register services. For example, the configuration services are added to the following class:
using ConfigSample.Options;
using Microsoft.Extensions.Configuration;
namespace Microsoft.Extensions.DependencyInjection
{
public static class MyConfigServiceCollectionExtensions
{
public static IServiceCollection AddConfig(
this IServiceCollection services, IConfiguration config)
{
services.Configure<PositionOptions>(
config.GetSection(PositionOptions.Position));
services.Configure<ColorOptions>(
config.GetSection(ColorOptions.Color));
return services;
}
public static IServiceCollection AddMyDependencyGroup(
this IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency>();
services.AddScoped<IMyDependency2, MyDependency2>();
return services;
}
}
}
The remaining services are registered in a similar class. The following code uses the new extension methods to register the services:
using Microsoft.Extensions.DependencyInjection.ConfigSample.Options;
var builder = WebApplication.CreateBuilder(args);
builder.Services
.AddConfig(builder.Configuration)
.AddMyDependencyGroup();
builder.Services.AddRazorPages();
var app = builder.Build();
Note: Each services.Add{GROUP_NAME}
extension method adds and potentially configures services. For example, AddControllersWithViews adds the services MVC controllers with views require, and AddRazorPages adds the services Razor Pages requires.
See Service lifetimes in Dependency injection in .NET
To use scoped services in middleware, use one of the following approaches:
Invoke
or InvokeAsync
method. Using constructor injection throws a runtime exception because it forces the scoped service to behave like a singleton. The sample in the Lifetime and registration options section demonstrates the InvokeAsync
approach.For more information, see Write custom ASP.NET Core middleware.
See Service registration methods in Dependency injection in .NET
It's common to use multiple implementations when mocking types for testing.
Registering a service with only an implementation type is equivalent to registering that service with the same implementation and service type. This is why multiple implementations of a service cannot be registered using the methods that don't take an explicit service type. These methods can register multiple instances of a service, but they will all have the same implementation type.
Any of the above service registration methods can be used to register multiple service instances of the same service type. In the following example, AddSingleton
is called twice with IMyDependency
as the service type. The second call to AddSingleton
overrides the previous one when resolved as IMyDependency
and adds to the previous one when multiple services are resolved via IEnumerable<IMyDependency>
. Services appear in the order they were registered when resolved via IEnumerable<{SERVICE}>
.
services.AddSingleton<IMyDependency, MyDependency>();
services.AddSingleton<IMyDependency, DifferentDependency>();
public class MyService
{
public MyService(IMyDependency myDependency,
IEnumerable<IMyDependency> myDependencies)
{
Trace.Assert(myDependency is DifferentDependency);
var dependencyArray = myDependencies.ToArray();
Trace.Assert(dependencyArray[0] is MyDependency);
Trace.Assert(dependencyArray[1] is DifferentDependency);
}
}
See Constructor injection behavior in Dependency injection in .NET
By default, Entity Framework contexts are added to the service container using the scoped lifetime because web app database operations are normally scoped to the client request. To use a different lifetime, specify the lifetime by using an AddDbContext overload. Services of a given lifetime shouldn't use a database context with a lifetime that's shorter than the service's lifetime.
To demonstrate the difference between service lifetimes and their registration options, consider the following interfaces that represent a task as an operation with an identifier, OperationId
. Depending on how the lifetime of an operation's service is configured for the following interfaces, the container provides either the same or different instances of the service when requested by a class:
public interface IOperation
{
string OperationId { get; }
}
public interface IOperationTransient : IOperation { }
public interface IOperationScoped : IOperation { }
public interface IOperationSingleton : IOperation { }
The following Operation
class implements all of the preceding interfaces. The Operation
constructor generates a GUID and stores the last 4 characters in the OperationId
property:
public class Operation : IOperationTransient, IOperationScoped, IOperationSingleton
{
public Operation()
{
OperationId = Guid.NewGuid().ToString()[^4..];
}
public string OperationId { get; }
}
The following code creates multiple registrations of the Operation
class according to the named lifetimes:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddTransient<IOperationTransient, Operation>();
builder.Services.AddScoped<IOperationScoped, Operation>();
builder.Services.AddSingleton<IOperationSingleton, Operation>();
var app = builder.Build();
if (!app.Environment.IsDevelopment())
{
app.UseExceptionHandler("/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseMyMiddleware();
app.UseRouting();
app.UseAuthorization();
app.MapRazorPages();
app.Run();
The sample app demonstrates object lifetimes both within and between requests. The IndexModel
and the middleware request each kind of IOperation
type and log the OperationId
for each:
public class IndexModel : PageModel
{
private readonly ILogger _logger;
private readonly IOperationTransient _transientOperation;
private readonly IOperationSingleton _singletonOperation;
private readonly IOperationScoped _scopedOperation;
public IndexModel(ILogger<IndexModel> logger,
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation)
{
_logger = logger;
_transientOperation = transientOperation;
_scopedOperation = scopedOperation;
_singletonOperation = singletonOperation;
}
public void OnGet()
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + _scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
}
}
Similar to the IndexModel
, the middleware resolves the same services:
public class MyMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger _logger;
private readonly IOperationSingleton _singletonOperation;
public MyMiddleware(RequestDelegate next, ILogger<MyMiddleware> logger,
IOperationSingleton singletonOperation)
{
_logger = logger;
_singletonOperation = singletonOperation;
_next = next;
}
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
}
public static class MyMiddlewareExtensions
{
public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<MyMiddleware>();
}
}
Scoped and transient services must be resolved in the InvokeAsync
method:
public async Task InvokeAsync(HttpContext context,
IOperationTransient transientOperation, IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
The logger output shows:
OperationId
value is different in the IndexModel
and in the middleware.To reduce the logging output, set "Logging:LogLevel:Microsoft:Error" in the appsettings.Development.json
file:
{
"MyKey": "MyKey from appsettings.Developement.json",
"Logging": {
"LogLevel": {
"Default": "Information",
"System": "Debug",
"Microsoft": "Error"
}
}
}
The following code shows how to resolve a scoped service for a limited duration when the app starts:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IMyDependency, MyDependency>();
var app = builder.Build();
using (var serviceScope = app.Services.CreateScope())
{
var services = serviceScope.ServiceProvider;
var myDependency = services.GetRequiredService<IMyDependency>();
myDependency.WriteMessage("Call services from main");
}
app.MapGet("/", () => "Hello World!");
app.Run();
See Constructor injection behavior in Dependency injection in .NET
For more information, see Scope validation.
Services and their dependencies within an ASP.NET Core request are exposed through HttpContext.RequestServices.
The framework creates a scope per request, and RequestServices
exposes the scoped service provider. All scoped services are valid for as long as the request is active.
नोट
Prefer requesting dependencies as constructor parameters over resolving services from RequestServices
. Requesting dependencies as constructor parameters yields classes that are easier to test.
When designing services for dependency injection:
If a class has a lot of injected dependencies, it might be a sign that the class has too many responsibilities and violates the Single Responsibility Principle (SRP). Attempt to refactor the class by moving some of its responsibilities into new classes. Keep in mind that Razor Pages page model classes and MVC controller classes should focus on UI concerns.
The container calls Dispose for the IDisposable types it creates. Services resolved from the container should never be disposed by the developer. If a type or factory is registered as a singleton, the container disposes the singleton automatically.
In the following example, the services are created by the service container and disposed automatically: dependency-injection\samples\6.x\DIsample2\DIsample2\Services\Service1.cs
public class Service1 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service1: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service1.Dispose");
_disposed = true;
}
}
public class Service2 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service2: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service2.Dispose");
_disposed = true;
}
}
public interface IService3
{
public void Write(string message);
}
public class Service3 : IService3, IDisposable
{
private bool _disposed;
public Service3(string myKey)
{
MyKey = myKey;
}
public string MyKey { get; }
public void Write(string message)
{
Console.WriteLine($"Service3: {message}, MyKey = {MyKey}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service3.Dispose");
_disposed = true;
}
}
using DIsample2.Services;
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddScoped<Service1>();
builder.Services.AddSingleton<Service2>();
var myKey = builder.Configuration["MyKey"];
builder.Services.AddSingleton<IService3>(sp => new Service3(myKey));
var app = builder.Build();
public class IndexModel : PageModel
{
private readonly Service1 _service1;
private readonly Service2 _service2;
private readonly IService3 _service3;
public IndexModel(Service1 service1, Service2 service2, IService3 service3)
{
_service1 = service1;
_service2 = service2;
_service3 = service3;
}
public void OnGet()
{
_service1.Write("IndexModel.OnGet");
_service2.Write("IndexModel.OnGet");
_service3.Write("IndexModel.OnGet");
}
}
The debug console shows the following output after each refresh of the Index page:
Service1: IndexModel.OnGet
Service2: IndexModel.OnGet
Service3: IndexModel.OnGet, MyKey = MyKey from appsettings.Developement.json
Service1.Dispose
Consider the following code:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRazorPages();
builder.Services.AddSingleton(new Service1());
builder.Services.AddSingleton(new Service2());
In the preceding code:
See IDisposable guidance for Transient and shared instance in Dependency injection in .NET
See Default service container replacement in Dependency injection in .NET
See Recommendations in Dependency injection in .NET
Avoid using the service locator pattern. For example, don't invoke GetService to obtain a service instance when you can use DI instead:
Incorrect:
Correct:
public class MyClass
{
private readonly IOptionsMonitor<MyOptions> _optionsMonitor;
public MyClass(IOptionsMonitor<MyOptions> optionsMonitor)
{
_optionsMonitor = optionsMonitor;
}
public void MyMethod()
{
var option = _optionsMonitor.CurrentValue.Option;
...
}
}
Another service locator variation to avoid is injecting a factory that resolves dependencies at runtime. Both of these practices mix Inversion of Control strategies.
Avoid static access to HttpContext
(for example, IHttpContextAccessor.HttpContext).
DI is an alternative to static/global object access patterns. You may not be able to realize the benefits of DI if you mix it with static object access.
Orchard Core is an application framework for building modular, multi-tenant applications on ASP.NET Core. For more information, see the Orchard Core Documentation.
See the Orchard Core samples for examples of how to build modular and multi-tenant apps using just the Orchard Core Framework without any of its CMS-specific features.
Program.cs
registers services that the app uses, including platform features, such as Entity Framework Core and ASP.NET Core MVC. Initially, the IServiceCollection
provided to Program.cs
has services defined by the framework depending on how the host was configured. For apps based on the ASP.NET Core templates, the framework registers more than 250 services.
The following table lists a small sample of these framework-registered services:
Service Type | Lifetime |
---|---|
Microsoft.AspNetCore.Hosting.Builder.IApplicationBuilderFactory | Transient |
IHostApplicationLifetime | Singleton |
IWebHostEnvironment | Singleton |
Microsoft.AspNetCore.Hosting.IStartup | Singleton |
Microsoft.AspNetCore.Hosting.IStartupFilter | Transient |
Microsoft.AspNetCore.Hosting.Server.IServer | Singleton |
Microsoft.AspNetCore.Http.IHttpContextFactory | Transient |
Microsoft.Extensions.Logging.ILogger<TCategoryName> | Singleton |
Microsoft.Extensions.Logging.ILoggerFactory | Singleton |
Microsoft.Extensions.ObjectPool.ObjectPoolProvider | Singleton |
Microsoft.Extensions.Options.IConfigureOptions<TOptions> | Transient |
Microsoft.Extensions.Options.IOptions<TOptions> | Singleton |
System.Diagnostics.DiagnosticSource | Singleton |
System.Diagnostics.DiagnosticListener | Singleton |
By Kirk Larkin, Steve Smith, Scott Addie, and Brandon Dahler
ASP.NET Core supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies.
For more information specific to dependency injection within MVC controllers, see Dependency injection into controllers in ASP.NET Core.
For information on using dependency injection in applications other than web apps, see Dependency injection in .NET.
For more information on dependency injection of options, see Options pattern in ASP.NET Core.
This topic provides information on dependency injection in ASP.NET Core. The primary documentation on using dependency injection is contained in Dependency injection in .NET.
View or download sample code (how to download)
A dependency is an object that another object depends on. Examine the following MyDependency
class with a WriteMessage
method that other classes depend on:
public class MyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage called. Message: {message}");
}
}
A class can create an instance of the MyDependency
class to make use of its WriteMessage
method. In the following example, the MyDependency
class is a dependency of the IndexModel
class:
public class IndexModel : PageModel
{
private readonly MyDependency _dependency = new MyDependency();
public void OnGet()
{
_dependency.WriteMessage("IndexModel.OnGet created this message.");
}
}
The class creates and directly depends on the MyDependency
class. Code dependencies, such as in the previous example, are problematic and should be avoided for the following reasons:
MyDependency
with a different implementation, the IndexModel
class must be modified.MyDependency
has dependencies, they must also be configured by the IndexModel
class. In a large project with multiple classes depending on MyDependency
, the configuration code becomes scattered across the app.MyDependency
class, which isn't possible with this approach.Dependency injection addresses these problems through:
Startup.ConfigureServices
method.In the sample app, the IMyDependency
interface defines the WriteMessage
method:
public interface IMyDependency
{
void WriteMessage(string message);
}
This interface is implemented by a concrete type, MyDependency
:
public class MyDependency : IMyDependency
{
public void WriteMessage(string message)
{
Console.WriteLine($"MyDependency.WriteMessage Message: {message}");
}
}
The sample app registers the IMyDependency
service with the concrete type MyDependency
. The AddScoped method registers the service with a scoped lifetime, the lifetime of a single request. Service lifetimes are described later in this topic.
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency>();
services.AddRazorPages();
}
In the sample app, the IMyDependency
service is requested and used to call the WriteMessage
method:
public class Index2Model : PageModel
{
private readonly IMyDependency _myDependency;
public Index2Model(IMyDependency myDependency)
{
_myDependency = myDependency;
}
public void OnGet()
{
_myDependency.WriteMessage("Index2Model.OnGet");
}
}
By using the DI pattern, the controller:
MyDependency
, only the IMyDependency
interface it implements. That makes it easy to change the implementation that the controller uses without modifying the controller.MyDependency
, it's created by the DI container.The implementation of the IMyDependency
interface can be improved by using the built-in logging API:
public class MyDependency2 : IMyDependency
{
private readonly ILogger<MyDependency2> _logger;
public MyDependency2(ILogger<MyDependency2> logger)
{
_logger = logger;
}
public void WriteMessage(string message)
{
_logger.LogInformation( $"MyDependency2.WriteMessage Message: {message}");
}
}
The updated ConfigureServices
method registers the new IMyDependency
implementation:
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency2>();
services.AddRazorPages();
}
MyDependency2
depends on ILogger<TCategoryName>, which it requests in the constructor. ILogger<TCategoryName>
is a framework-provided service.
It's not unusual to use dependency injection in a chained fashion. Each requested dependency in turn requests its own dependencies. The container resolves the dependencies in the graph and returns the fully resolved service. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph.
The container resolves ILogger<TCategoryName>
by taking advantage of (generic) open types, eliminating the need to register every (generic) constructed type.
In dependency injection terminology, a service:
IMyDependency
service.The framework provides a robust logging system. The IMyDependency
implementations shown in the preceding examples were written to demonstrate basic DI, not to implement logging. Most apps shouldn't need to write loggers. The following code demonstrates using the default logging, which doesn't require any services to be registered in ConfigureServices
:
public class AboutModel : PageModel
{
private readonly ILogger _logger;
public AboutModel(ILogger<AboutModel> logger)
{
_logger = logger;
}
public string Message { get; set; }
public void OnGet()
{
Message = $"About page visited at {DateTime.UtcNow.ToLongTimeString()}";
_logger.LogInformation(Message);
}
}
Using the preceding code, there is no need to update ConfigureServices
, because logging is provided by the framework.
Services can be injected into the Startup
constructor and the Startup.Configure
method.
Only the following services can be injected into the Startup
constructor when using the Generic Host (IHostBuilder):
Any service registered with the DI container can be injected into the Startup.Configure
method:
public void Configure(IApplicationBuilder app, ILogger<Startup> logger)
{
...
}
For more information, see App startup in ASP.NET Core and Access configuration in Startup.
The ASP.NET Core framework uses a convention for registering a group of related services. The convention is to use a single Add{GROUP_NAME}
extension method to register all of the services required by a framework feature. For example, the AddControllers extension method registers the services required for MVC controllers.
The following code is generated by the Razor Pages template using individual user accounts and shows how to add additional services to the container using the extension methods AddDbContext and AddDefaultIdentity:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(
Configuration.GetConnectionString("DefaultConnection")));
services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
.AddEntityFrameworkStores<ApplicationDbContext>();
services.AddRazorPages();
}
Consider the following ConfigureServices
method, which registers services and configures options:
public void ConfigureServices(IServiceCollection services)
{
services.Configure<PositionOptions>(
Configuration.GetSection(PositionOptions.Position));
services.Configure<ColorOptions>(
Configuration.GetSection(ColorOptions.Color));
services.AddScoped<IMyDependency, MyDependency>();
services.AddScoped<IMyDependency2, MyDependency2>();
services.AddRazorPages();
}
Related groups of registrations can be moved to an extension method to register services. For example, the configuration services are added to the following class:
using ConfigSample.Options;
using Microsoft.Extensions.Configuration;
namespace Microsoft.Extensions.DependencyInjection
{
public static class MyConfigServiceCollectionExtensions
{
public static IServiceCollection AddConfig(
this IServiceCollection services, IConfiguration config)
{
services.Configure<PositionOptions>(
config.GetSection(PositionOptions.Position));
services.Configure<ColorOptions>(
config.GetSection(ColorOptions.Color));
return services;
}
public static IServiceCollection AddMyDependencyGroup(
this IServiceCollection services)
{
services.AddScoped<IMyDependency, MyDependency>();
services.AddScoped<IMyDependency2, MyDependency2>();
return services;
}
}
}
The remaining services are registered in a similar class. The following ConfigureServices
method uses the new extension methods to register the services:
public void ConfigureServices(IServiceCollection services)
{
services.AddConfig(Configuration)
.AddMyDependencyGroup();
services.AddRazorPages();
}
Note: Each services.Add{GROUP_NAME}
extension method adds and potentially configures services. For example, AddControllersWithViews adds the services MVC controllers with views require, and AddRazorPages adds the services Razor Pages requires. We recommend that apps follow the naming convention of creating extension methods in the Microsoft.Extensions.DependencyInjection namespace. Creating extension methods in the Microsoft.Extensions.DependencyInjection
namespace:
See Service lifetimes in Dependency injection in .NET
To use scoped services in middleware, use one of the following approaches:
Invoke
or InvokeAsync
method. Using constructor injection throws a runtime exception because it forces the scoped service to behave like a singleton. The sample in the Lifetime and registration options section demonstrates the InvokeAsync
approach.InvokeAsync
method.For more information, see Write custom ASP.NET Core middleware.
See Service registration methods in Dependency injection in .NET
It's common to use multiple implementations when mocking types for testing.
Registering a service with only an implementation type is equivalent to registering that service with the same implementation and service type. This is why multiple implementations of a service cannot be registered using the methods that don't take an explicit service type. These methods can register multiple instances of a service, but they will all have the same implementation type.
Any of the above service registration methods can be used to register multiple service instances of the same service type. In the following example, AddSingleton
is called twice with IMyDependency
as the service type. The second call to AddSingleton
overrides the previous one when resolved as IMyDependency
and adds to the previous one when multiple services are resolved via IEnumerable<IMyDependency>
. Services appear in the order they were registered when resolved via IEnumerable<{SERVICE}>
.
services.AddSingleton<IMyDependency, MyDependency>();
services.AddSingleton<IMyDependency, DifferentDependency>();
public class MyService
{
public MyService(IMyDependency myDependency,
IEnumerable<IMyDependency> myDependencies)
{
Trace.Assert(myDependency is DifferentDependency);
var dependencyArray = myDependencies.ToArray();
Trace.Assert(dependencyArray[0] is MyDependency);
Trace.Assert(dependencyArray[1] is DifferentDependency);
}
}
See Constructor injection behavior in Dependency injection in .NET
By default, Entity Framework contexts are added to the service container using the scoped lifetime because web app database operations are normally scoped to the client request. To use a different lifetime, specify the lifetime by using an AddDbContext overload. Services of a given lifetime shouldn't use a database context with a lifetime that's shorter than the service's lifetime.
To demonstrate the difference between service lifetimes and their registration options, consider the following interfaces that represent a task as an operation with an identifier, OperationId
. Depending on how the lifetime of an operation's service is configured for the following interfaces, the container provides either the same or different instances of the service when requested by a class:
public interface IOperation
{
string OperationId { get; }
}
public interface IOperationTransient : IOperation { }
public interface IOperationScoped : IOperation { }
public interface IOperationSingleton : IOperation { }
The following Operation
class implements all of the preceding interfaces. The Operation
constructor generates a GUID and stores the last 4 characters in the OperationId
property:
public class Operation : IOperationTransient, IOperationScoped, IOperationSingleton
{
public Operation()
{
OperationId = Guid.NewGuid().ToString()[^4..];
}
public string OperationId { get; }
}
The Startup.ConfigureServices
method creates multiple registrations of the Operation
class according to the named lifetimes:
public void ConfigureServices(IServiceCollection services)
{
services.AddTransient<IOperationTransient, Operation>();
services.AddScoped<IOperationScoped, Operation>();
services.AddSingleton<IOperationSingleton, Operation>();
services.AddRazorPages();
}
The sample app demonstrates object lifetimes both within and between requests. The IndexModel
and the middleware request each kind of IOperation
type and log the OperationId
for each:
public class IndexModel : PageModel
{
private readonly ILogger _logger;
private readonly IOperationTransient _transientOperation;
private readonly IOperationSingleton _singletonOperation;
private readonly IOperationScoped _scopedOperation;
public IndexModel(ILogger<IndexModel> logger,
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation)
{
_logger = logger;
_transientOperation = transientOperation;
_scopedOperation = scopedOperation;
_singletonOperation = singletonOperation;
}
public void OnGet()
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + _scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
}
}
Similar to the IndexModel
, the middleware resolves the same services:
public class MyMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger _logger;
private readonly IOperationTransient _transientOperation;
private readonly IOperationSingleton _singletonOperation;
public MyMiddleware(RequestDelegate next, ILogger<MyMiddleware> logger,
IOperationTransient transientOperation,
IOperationSingleton singletonOperation)
{
_logger = logger;
_transientOperation = transientOperation;
_singletonOperation = singletonOperation;
_next = next;
}
public async Task InvokeAsync(HttpContext context,
IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
}
public static class MyMiddlewareExtensions
{
public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<MyMiddleware>();
}
}
Scoped services must be resolved in the InvokeAsync
method:
public async Task InvokeAsync(HttpContext context,
IOperationScoped scopedOperation)
{
_logger.LogInformation("Transient: " + _transientOperation.OperationId);
_logger.LogInformation("Scoped: " + scopedOperation.OperationId);
_logger.LogInformation("Singleton: " + _singletonOperation.OperationId);
await _next(context);
}
The logger output shows:
OperationId
value is different in the IndexModel
and in the middleware.To reduce the logging output, set "Logging:LogLevel:Microsoft:Error" in the appsettings.Development.json
file:
{
"MyKey": "MyKey from appsettings.Developement.json",
"Logging": {
"LogLevel": {
"Default": "Information",
"System": "Debug",
"Microsoft": "Error"
}
}
}
Create an IServiceScope with IServiceScopeFactory.CreateScope to resolve a scoped service within the app's scope. This approach is useful to access a scoped service at startup to run initialization tasks.
The following example shows how to access the scoped IMyDependency
service and call its WriteMessage
method in Program.Main
:
public class Program
{
public static void Main(string[] args)
{
var host = CreateHostBuilder(args).Build();
using (var serviceScope = host.Services.CreateScope())
{
var services = serviceScope.ServiceProvider;
try
{
var myDependency = services.GetRequiredService<IMyDependency>();
myDependency.WriteMessage("Call services from main");
}
catch (Exception ex)
{
var logger = services.GetRequiredService<ILogger<Program>>();
logger.LogError(ex, "An error occurred.");
}
}
host.Run();
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
}
See Constructor injection behavior in Dependency injection in .NET
For more information, see Scope validation.
Services and their dependencies within an ASP.NET Core request are exposed through HttpContext.RequestServices.
The framework creates a scope per request, and RequestServices
exposes the scoped service provider. All scoped services are valid for as long as the request is active.
नोट
Prefer requesting dependencies as constructor parameters over resolving services from RequestServices
. Requesting dependencies as constructor parameters yields classes that are easier to test.
When designing services for dependency injection:
If a class has a lot of injected dependencies, it might be a sign that the class has too many responsibilities and violates the Single Responsibility Principle (SRP). Attempt to refactor the class by moving some of its responsibilities into new classes. Keep in mind that Razor Pages page model classes and MVC controller classes should focus on UI concerns.
The container calls Dispose for the IDisposable types it creates. Services resolved from the container should never be disposed by the developer. If a type or factory is registered as a singleton, the container disposes the singleton automatically.
In the following example, the services are created by the service container and disposed automatically:
public class Service1 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service1: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service1.Dispose");
_disposed = true;
}
}
public class Service2 : IDisposable
{
private bool _disposed;
public void Write(string message)
{
Console.WriteLine($"Service2: {message}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service2.Dispose");
_disposed = true;
}
}
public interface IService3
{
public void Write(string message);
}
public class Service3 : IService3, IDisposable
{
private bool _disposed;
public Service3(string myKey)
{
MyKey = myKey;
}
public string MyKey { get; }
public void Write(string message)
{
Console.WriteLine($"Service3: {message}, MyKey = {MyKey}");
}
public void Dispose()
{
if (_disposed)
return;
Console.WriteLine("Service3.Dispose");
_disposed = true;
}
}
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<Service1>();
services.AddSingleton<Service2>();
var myKey = Configuration["MyKey"];
services.AddSingleton<IService3>(sp => new Service3(myKey));
services.AddRazorPages();
}
public class IndexModel : PageModel
{
private readonly Service1 _service1;
private readonly Service2 _service2;
private readonly IService3 _service3;
public IndexModel(Service1 service1, Service2 service2, IService3 service3)
{
_service1 = service1;
_service2 = service2;
_service3 = service3;
}
public void OnGet()
{
_service1.Write("IndexModel.OnGet");
_service2.Write("IndexModel.OnGet");
_service3.Write("IndexModel.OnGet");
}
}
The debug console shows the following output after each refresh of the Index page:
Service1: IndexModel.OnGet
Service2: IndexModel.OnGet
Service3: IndexModel.OnGet, MyKey = My Key from config
Service1.Dispose
Consider the following code:
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton(new Service1());
services.AddSingleton(new Service2());
services.AddRazorPages();
}
In the preceding code:
See IDisposable guidance for Transient and shared instance in Dependency injection in .NET
See Default service container replacement in Dependency injection in .NET
See Recommendations in Dependency injection in .NET
Avoid using the service locator pattern. For example, don't invoke GetService to obtain a service instance when you can use DI instead:
Incorrect:
Correct:
public class MyClass
{
private readonly IOptionsMonitor<MyOptions> _optionsMonitor;
public MyClass(IOptionsMonitor<MyOptions> optionsMonitor)
{
_optionsMonitor = optionsMonitor;
}
public void MyMethod()
{
var option = _optionsMonitor.CurrentValue.Option;
...
}
}
Another service locator variation to avoid is injecting a factory that resolves dependencies at runtime. Both of these practices mix Inversion of Control strategies.
Avoid static access to HttpContext
(for example, IHttpContextAccessor.HttpContext).
Avoid calls to BuildServiceProvider in ConfigureServices
. Calling BuildServiceProvider
typically happens when the developer wants to resolve a service in ConfigureServices
. For example, consider the case where the LoginPath
is loaded from configuration. Avoid the following approach:
In the preceding image, selecting the green wavy line under services.BuildServiceProvider
shows the following ASP0000 warning:
ASP0000 Calling 'BuildServiceProvider' from application code results in an additional copy of singleton services being created. Consider alternatives such as dependency injecting services as parameters to 'Configure'.
Calling BuildServiceProvider
creates a second container, which can create torn singletons and cause references to object graphs across multiple containers.
A correct way to get LoginPath
is to use the options pattern's built-in support for DI:
public void ConfigureServices(IServiceCollection services)
{
services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
.AddCookie();
services.AddOptions<CookieAuthenticationOptions>(
CookieAuthenticationDefaults.AuthenticationScheme)
.Configure<IMyService>((options, myService) =>
{
options.LoginPath = myService.GetLoginPath();
});
services.AddRazorPages();
}
Disposable transient services are captured by the container for disposal. This can turn into a memory leak if resolved from the top level container.
Enable scope validation to make sure the app doesn't have singletons that capture scoped services. For more information, see Scope validation.
Like all sets of recommendations, you may encounter situations where ignoring a recommendation is required. Exceptions are rare, mostly special cases within the framework itself.
DI is an alternative to static/global object access patterns. You may not be able to realize the benefits of DI if you mix it with static object access.
Orchard Core is an application framework for building modular, multi-tenant applications on ASP.NET Core. For more information, see the Orchard Core Documentation.
See the Orchard Core samples for examples of how to build modular and multi-tenant apps using just the Orchard Core Framework without any of its CMS-specific features.
The Startup.ConfigureServices
method registers services that the app uses, including platform features, such as Entity Framework Core and ASP.NET Core MVC. Initially, the IServiceCollection
provided to ConfigureServices
has services defined by the framework depending on how the host was configured. For apps based on the ASP.NET Core templates, the framework registers more than 250 services.
The following table lists a small sample of these framework-registered services:
Service Type | Lifetime |
---|---|
Microsoft.AspNetCore.Hosting.Builder.IApplicationBuilderFactory | Transient |
IHostApplicationLifetime | Singleton |
IWebHostEnvironment | Singleton |
Microsoft.AspNetCore.Hosting.IStartup | Singleton |
Microsoft.AspNetCore.Hosting.IStartupFilter | Transient |
Microsoft.AspNetCore.Hosting.Server.IServer | Singleton |
Microsoft.AspNetCore.Http.IHttpContextFactory | Transient |
Microsoft.Extensions.Logging.ILogger<TCategoryName> | Singleton |
Microsoft.Extensions.Logging.ILoggerFactory | Singleton |
Microsoft.Extensions.ObjectPool.ObjectPoolProvider | Singleton |
Microsoft.Extensions.Options.IConfigureOptions<TOptions> | Transient |
Microsoft.Extensions.Options.IOptions<TOptions> | Singleton |
System.Diagnostics.DiagnosticSource | Singleton |
System.Diagnostics.DiagnosticListener | Singleton |
ASP.NET Core प्रतिक्रिया
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