添加后台服务，每7天删除一次数据

Question

我有一个类Issue，其中包含一些信息，包括他们的日期。我想创建一个后台服务，从数据库中删除超过7天的数据。

下面是我试过的代码:

using APIExample;
using Microsoft.Identity.Client;
public class BackgroundWorker : BackgroundService
{
private readonly AppDbContext _appDbContext;
public BackgroundWorker(AppDbContext appDbContext)
{
_appDbContext = appDbContext;
}
protected override Task ExecuteAsync(CancellationToken stoppingToken)
{
_appDbContext.Issue.RemoveRange(_appDbContext.Issue.Where(a => (a.Created.AddDays(7) >= DateTime.Now)));
_appDbContext.SaveChanges();
return Task.CompletedTask;
}
}

我已经在program.cs类中注入了这个

builder.Services.AddHostedService<BackgroundWorker>();

这是我得到的错误:

系统。AggregateException: '一些服务不能被构造(在验证服务描述符时出错'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton ImplementationType: BackgroundWorker': Cannot consume scoped service 'APIExample。AppDbContext' from singleton 'Microsoft.Extensions.Hosting.IHostedService'.)'

Answer 1

不能像这样注入DbContext，使用ServiceScopeFactory

public class BackgroundWorker : BackgroundService
{
private readonly IServiceScopeFactory _serviceScopeFactory;


public BackgroundWorker(IServiceScopeFactory serviceScopeFactory)
{
_serviceScopeFactory = serviceScopeFactory;
}

protected override Task ExecuteAsync(CancellationToken stoppingToken)
{
using (var scope = _serviceScopeFactory.CreateScope())
{
var _appDbContext= scope.ServiceProvider.GetService<AppDbContext>();
_appDbContext.Issue.RemoveRange(_appDbContext.Issue.Where(a => (a.Created.AddDays(7) >= DateTime.Now)));
_appDbContext.SaveChanges();
return Task.CompletedTask;
}
}
}