如何在 ASP.NET Core 的单一实例服务中使用作用域服务

在 ASP.NET Core 中，有三种类型的依赖注入服务。您可以在此处详细阅读它们。在这篇文章中，我们将重点介绍如何在单例服务中使用作用域内服务。

在单例服务中使用作用域服务的主要目标是访问单例服务中不可用的特定于请求的数据或资源。例如，您可能希望从单一实例服务（如后台服务、缓存服务或通知服务）访问数据库上下文、配置服务或用户服务。

在单例服务中使用作用域服务的主要挑战是手动管理作用域的生存期和处置。由于单一实例服务没有请求作用域，因此需要使用 创建作用域，并在完成作用域服务后释放它。您还需要使用 或 等方法从作用域的服务提供程序解析作用域服务。IServiceScopeFactoryGetRequiredServiceGetService

如果未正确创建和释放作用域，则可能会遇到错误或内存泄漏等错误。您还需要处理在作用域内使用作用域服务时可能发生的任何异常。InvalidOperationException: Cannot resolve scoped service from root provider

可能需要在单一实例服务中使用作用域内服务的一些方案示例包括：

public classMyBackgroundService : BackgroundService
{
privatereadonlyIServiceScopeFactory _scopeFactory;
publicMyBackgroundService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
protectedoverrideasyncTaskExecuteAsync(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();
// ...
}
}
}


public classMyCacheService
{
privatereadonlyIServiceScopeFactory _scopeFactory;
publicMyCacheService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
// Define a method to get data from the cache
publicasyncTask<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.Getp("CacheSettings").Get<CacheSettings>();
// Do something with the cache settings
var cache = newDistributedCache(cacheSettings);
// Get data from the cache
var data = await cache.GetAsync<T>(key);
return data;
}
}
}


public classMyNotificationService
{
privatereadonlyIServiceScopeFactory _scopeFactory;
publicMyNotificationService(IServiceScopeFactory scopeFactory)
{
_scopeFactory = scopeFactory;
}
// Define a method to send notifications to users
publicasyncTaskSendNotificationAsync(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 = newEmailService();
var smsService = newSmsService();
// Send notifications to the user via email and SMS
await emailService.SendEmailAsync(email, message);
await smsService.SendSmsAsync(phone, message);
}
}
}


在单一实例服务中使用作用域服务的优点和缺点包括：

优势 ：

缺点 ：