How to Use Scoped Services within Singleton Services in ASP.NET Core: A Practical Guide with Code Examples
In ASP.NET Core, there are three types of dependency injection services. You can read them in detail here. In this post, we are focusing on how to use a scoped service within a singleton service.
The main goal of using scoped services within singleton services is to access request-specific data or resources that are not available in the singleton service. For example, you might want to access the database context, the configuration service, or the user service from a singleton service, such as a background service, a cache service, or a notification service.
The main challenge of using scoped services within singleton services is to manage the scope’s lifetime and disposal manually. Since the singleton service does not have a request scope, you need to create a scope using the IServiceScopeFactory and dispose it when you are done with the scoped service. You also need to resolve the scoped service from the scope’s service provider, using methods such as GetRequiredService or GetService.
If you do not create and dispose the scope properly, you might encounter errors such as InvalidOperationException: Cannot resolve scoped service from root provider or memory leaks. You also need to handle any exceptions that might occur while using the scoped service within the scope.
Some examples of scenarios where you might need to use scoped services within singleton services are:
- A background service that runs periodically and needs to access the database context to perform some operations. The database context is a scoped service that depends on the current request, so you need to create a scope manually and resolve the database context within the scope.
public class MyBackgroundService : BackgroundService
{
private readonly IServiceScopeFactory _scopeFactory;
public MyBackgroundService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
// Create a scope using the CreateScope method
using (var scope = _scopeFactory.CreateScope())
{
// Resolve the database context using the GetRequiredService method
var dbContext = scope.ServiceProvider.GetRequiredService<MyDbContext>();
// Do something with the database context
var users = await dbContext.Users.ToListAsync();
// ...
}
}
}- A cache service that stores and retrieves data from a distributed cache. The cache service is a singleton service that is shared by the entire application, but it needs to access the configuration service to get the cache settings. The configuration service is a scoped service that depends on the current request, so you need to create a scope manually and resolve the configuration service within the scope.
public class MyCacheService
{
private readonly IServiceScopeFactory _scopeFactory;
public MyCacheService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
// Define a method to get data from the cache
public async Task<T> GetDataAsync<T>(string key)
{
// Create a scope using the CreateScope method
using (var scope = _scopeFactory.CreateScope())
{
// Resolve the configuration service using the GetService method
var configuration = scope.ServiceProvider.GetService<IConfiguration>();
// Get the cache settings from the configuration
var cacheSettings = configuration.GetSection("CacheSettings").Get<CacheSettings>();
// Do something with the cache settings
var cache = new DistributedCache(cacheSettings);
// Get data from the cache
var data = await cache.GetAsync<T>(key);
return data;
}
}
}- A notification service that sends notifications to users via email or SMS. The notification service is a singleton service that is shared by the entire application, but it needs to access the user service to get the user’s contact information. The user service is a scoped service that depends on the current request, so you need to create a scope manually and resolve the user service within the scope.
public class MyNotificationService
{
private readonly IServiceScopeFactory _scopeFactory;
public MyNotificationService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
// Define a method to send notifications to users
public async Task SendNotificationAsync(string message, int userId)
{
// Create a scope using the CreateScope method
using (var scope = _scopeFactory.CreateScope())
{
// Resolve the user service using the GetRequiredService method
var userService = scope.ServiceProvider.GetRequiredService<IUserService>();
// Get the user's contact information from the user service
var user = await userService.GetUserByIdAsync(userId);
var email = user.Email;
var phone = user.Phone;
// Do something with the contact information
var emailService = new EmailService();
var smsService = new SmsService();
// Send notifications to the user via email and SMS
await emailService.SendEmailAsync(email, message);
await smsService.SendSmsAsync(phone, message);
}
}
}The benefits and drawbacks of using scoped services within singleton services are:
Benefits:
- You can avoid concurrency issues that might occur if you use singleton services to access request-specific data or resources. For example, if you use a singleton service to access the database context, you might encounter errors such as
InvalidOperationException: A second operation started on this context before a previous operation completedorObjectDisposedException: Cannot access a disposed object. By using scoped services within singleton services, you can ensure that each request has its own instance of the database context and avoid these errors. - You can ensure proper disposal of the scoped services and their dependencies. For example, if you use a singleton service to access the database context, you might forget to dispose it or dispose it too early, which could cause memory leaks or data corruption. By using scoped services within singleton services, you can ensure that the scope is disposed at the end of the request and the database context is disposed along with it.
Drawbacks:
- You can add some complexity and overhead to your code and performance. For example, if you use scoped services within singleton services, you need to inject an
IServiceScopeFactoryinto your singleton service, create and dispose a scope manually, and resolve the scoped service from the scope’s service provider. This adds some extra code and logic to your singleton service, which could make it harder to read and maintain. It also adds some extra memory and CPU usage to create and dispose the scopes and resolve the services, which could affect your performance.
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