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How to use lifetimes in ASP.NET Core dependency injection?
How to use lifetimes in ASP.NET Core dependency injection?

Dependency injection code example for ASP.NET Core

We have a number of dependency injection tutorials which include explaining the different service lifetimes, injecting services into classes, keyed services, creating a new scope, unit testing and the common mistakes of dependency injection.

Download the code example

You'll need to fill out the code example form. We will send you an email where you can download the code example.

The code example will be in a zip file and will include all the dependency injection tutorials separated by a numeric folder name.

Software

This is the software that will need to be installed onto your machine.

Tutorials

Here are the different dependency injection tutorials available:

How to use lifetimes in ASP.NET Core dependency injection?

You can read more about how to use the different lifetimes in ASP.NET Core or you can watch the video:

In Visual Studio, open up 01/RoundTheCode.DI._01.sln from the code example zip file that you downloaded.

You can test the different ways to register a service by changing the dependencyTypeEnum variable in Program.cs.  You can change it to:

  • Type - This registers a service by providing the types as parameters
  • Generic - This registers a service by providing the types using the generic class extension method
  • ImplementationType - Allows you to explicitly create the service instance. The types are provided as parameters.
  • ImplementationGeneric - Allows you to explicitly create the service instance. The types are provided using the generic class extension method

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1.

To test the differences with the singleton, scoped and transient, run https://localhost:7058/api/WebApi/service-lifetimes.

If you want to test how the transient service lifetime works when injected into a different part of the request, run https://localhost:7058/mvc/service-lifetimes.

How to inject services in ASP.NET Core dependency injection

You can read more about how to inject services in ASP.NET Core or you can watch the video:

In Visual Studio, open up 02/RoundTheCode.DI._02.sln from the code example zip file that you downloaded.

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1.

Here is what you can test:

Minimal APIs

  • Endpoint that injects services - https://localhost:7058/minimal/categories

Web APIs

  • Endpoint that uses services that are referenced in private readonly fields - https://localhost:7058/api/WebApi/categories
  • Injects a service through an endpoint - https://localhost:7058/api/WebApi/computers
  • Using a class in an endpoint that injects a service using primary constructors - https://localhost:7058/api/WebApi/primary

MVC controllers and Razor views

  • Razor view that injects services - https://localhost:7058/Mvc/categories
  • The [FromService] attribute used to inject a service through an endpoint - https://localhost:7058/Mvc/computers

Breakpoints

  • The CategoryMiddleware class is run on every request. You can add a breakpoint to see how it behaves when injecting services

Use keyed services for multiple implementations of a service

You can read more about how to register and inject keyed services or you can watch the video:

In Visual Studio, open up 03/RoundTheCode.DI._03.sln from the code example zip file that you downloaded.

You can test the different ways to register a keyed service by changing the dependencyTypeEnum variable in Program.cs.  You can change it to:

  • Type - This registers a keyed service by providing the types as parameters
  • Generic - This registers a keyed service by providing the types using the generic class extension method
  • ImplementationType - Allows you to explicitly create the service instance. The types are provided as parameters.
  • ImplementationGeneric - Allows you to explicitly create the service instance. The types are provided using the generic class extension method

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1.

Here is what else you can test:

Minimal APIs

  • Endpoint that injects keyed services - https://localhost:7058/minimal/service-lifetimes

Web APIs

  • Endpoint that uses services that are referenced in private readonly fields - https://localhost:7058/api/WebApi/service-lifetimes
  • Injects a service through an endpoint - https://localhost:7058/api/WebApi/product-singleton-1-utc
  • Add two different implementations of the same non-keyed service and injecting the service - https://localhost:7058/api/WebApiStorage/last-category-type
  • Add two different implementations of the same non-keyed service and injecting the service using an IEnumerable - https://localhost:7058/api/WebApiStorage/category-types
  • Add two different implementations of the same service using keyed services - https://localhost:7058/api/WebApiStorage/category-keyed-types

Primary constructors

  • Using a class in a Web API controller endpoint that injects a service using primary constructors - https://localhost:7058/api/WebApiStorage/category-primary-types

MVC controllers and Razor views

  • Razor view that injects services - https://localhost:7058/mvc/service-lifetimes

Breakpoints

  • The ProductMiddleware class is run on every request. You can add a breakpoint to see how it behaves when injecting services

GetService or GetRequiredService in IServiceProvider?

You can read more about whether to use GetService or GetRequiredService when using the IServiceProvider type or you can watch the video:

In Visual Studio, open up 04/RoundTheCode.DI._04.sln from the code example zip file that you downloaded.

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1.

This is what you can test:

Minimal APIs

  • Resolve services that have been registered - https://localhost:7058/minimal/service-provider
  • Try to resolve services that haven't been registered using GetService and GetKeyedService - https://localhost:7058/minimal/service-provider-null
  • Try to resolve a service that hasn't been registered using GetRequiredService - https://localhost:7058/minimal/service-provider-null-required-service. This should throw an InvalidOperationException
  • Try to resolve a keyed service that hasn't been registered using GetRequiredKeyedService - https://localhost:7058/minimal/service-provider-null-required-keyed-service. This should throw an InvalidOperationException

You can append ?type=HttpContext to each of these endpoints to resolve the services using HttpContext.RequestServices.

Web APIs

  • Resolve services that have been registered - https://localhost:7058/api/WebApi/service-provider
  • Try to resolve services that haven't been registered using GetService and GetKeyedService - https://localhost:7058/api/WebApi/service-provider-null
  • Try to resolve a service that hasn't been registered using GetRequiredService - https://localhost:7058/api/WebApi/service-provider-null-required-service. This should throw an InvalidOperationException
  • Try to resolve a keyed service that hasn't been registered using GetRequiredKeyedService - https://localhost:7058/api/WebApi/service-provider-null-required-keyed-service. This should throw an InvalidOperationException

You can append ?type=HttpContext to each of these endpoints to resolve the services using HttpContext.RequestServices.

MVC controllers and Razor views

  • Resolve services that have been registered - https://localhost:7058/Mvc/service-provider
  • Try to resolve services that haven't been registered using GetService and GetKeyedService - https://localhost:7058/Mvc/service-provider-null
  • Try to resolve a service that hasn't been registered using GetRequiredService - https://localhost:7058/Mvc/service-provider-null-required-service. This should throw an InvalidOperationException
  • Try to resolve a keyed service that hasn't been registered using GetRequiredKeyedService - https://localhost:7058/Mvc/service-provider-null-required-keyed-service. This should throw an InvalidOperationException

You can append ?type=HttpContext to each of these endpoints to resolve the services using HttpContext.RequestServices.

Primary constructors

  • Use GetService, GetRequiredService, GetKeyedService and GetRequiredKeyedService by injecting the IServiceProvider into a primary constructor class - https://localhost:7058/api/WebApiPrimary

Breakpoints

  • You can put a breakpoint in Program.cs to test resolving services before the application runs using app.Services
  • You can put a breakpoint in the InvokeAsync method inside the ServiceProviderMiddleware class to test the IServiceProvider type in middleware. You can change the ServiceProviderTypeEnum in the GetServiceTypeInstance method to ServiceProviderTypeEnum.HttpContext to test resolving the services from HttpContext.RequestServices

How do you resolve scoped services in a background service?

You can read more about how to resolve scoped services in a background service, or watch the video.

In Visual Studio, open up 05/RoundTheCode.DI._05.sln from the code example zip file that you downloaded.

There are two projects contained within the solution.

Hosted service

RoundTheCode.DI.Worker is a background service that creates a new scope and resolves the ICategoryScopedService, ICategoryTransientService services and the ICategoryStorageService keyed service with that scope.

In Visual Studio 2022, go to Project and Configure Startup Projects in the top menu. On the left-hand side, select Common Properties and Configure Startup Projects. Select the Single Startup Project: radio button, select RoundTheCode.DI.Worker and press OK.

Run the application. It should output three timestamps to the console window every second.

Web API

RoundTheCode.DI has a WebApiController class which is a controller that has methods which use multithreading.

In Visual Studio 2022, go to Project and Configure Startup Projects in the top menu. On the left-hand side, select Common Properties and Configure Startup Projects. Select the Single Startup Project: radio button, select RoundTheCode.DI and press OK.

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1. This is what you can test:

  • https://localhost:7058/api/WebApi/multiple-threads-unique-scope - This returns an empty 200 response. It runs three tasks simultaneously which each task creating a new scope and outputs a task number and datestamp to the console. The empty response is returned when all three tasks are completed. It should output the task number and datestamp for each task.
  • https://localhost:7058/api/WebApi/multiple-threads-shared-scope - This returns an empty 200 response. It runs three tasks simultaneously but shares the same scope with each one. It outputs a task number and datestamp to the console. The empty response is returned when any of the three tasks are completed. You'll probably find that not all of the tasks will output a task number and datestamp as the scope will have already been disposed before resolving the service.

How to write xUnit tests for dependency injection services

You can read more about how to write xUnit tests for dependency injection services, or watch the video:

In Visual Studio, open up 06/RoundTheCode.DI._06.sln from the code example zip file that you downloaded. There are two projects contained within the solution.

  • RoundTheCode.DI - ASP.NET Core Web API
  • RoundTheCode.DI.Tests - xUnit test project that unit test classes that are in RoundTheCode.DI

In the top menu, you can go to Test and Test Explorer. This allows you to run all four tests that are in the xUnit test project. They should all pass.

Common errors to avoid in ASP.NET Core dependency injection

You can read more about the common errors to avoid in ASP.NET Core dependency injection, or watch the video:

In Visual Studio, open up 07/RoundTheCode.DI._07.sln from the code example zip file that you downloaded.

Run the application and it will load up the Scalar OpenAPI document on https://localhost:7058/scalar/v1.

Here is what you can test:

Failing to register a dependency

  • In Program.cs, set the exception variable to ExceptionEnum.NoRegisterResolution (This is the default value)
  • Run https://localhost:7058/api/webapinotadded and you'll get the exception
  • Resolve it in Program.cs by setting the exception variable to ExceptionEnum.NoRegisterResolution

Circular dependency

  • In Program.cs, set the exception variable to ExceptionEnum.CircularDependencyException
  • Run the application and you will get the exception

Injecting a scoped service lifetime into a singleton

  • In Program.cs, set the exception variable to ExceptionEnum.ScopedIntoSingletonException
  • Run the application and you will get the exception
  • Resolve it in Program.cs by setting the exception variable to ExceptionEnum.ScopedIntoSingletonResolution and run https://localhost:7058/api/webapisingletonscope to resolve a scoped service using a new scope

Ambiguous constructors

  • In Program.cs, set the exception variable to ExceptionEnum.AmbiguousException
  • Run the application and you will get the exception
  • Resolve it in Program.cs by setting the exception variable to ExceptionEnum.AmbiguousResolution. No exception will be thrown

Sharing scope and transient service lifetimes across multiple threads

  • In Program.cs, set the exception variable to ExceptionEnum.MultipleThreads
  • Run https://localhost:7058/api/WebApiSharedScope/shared-service and then view the console application logs to see one datestamp outputted
  • Run https://localhost:7058/api/WebApiSharedScope/shared-service-fix and then view the console application logs to see two datestamps outputted