我在 ASP.Net Core
应用程序的 Startup
类中添加了一个 Timer
。它会在某个时间段触发并执行诸如记录示例文本之类的操作。我需要它能够执行数据库驱动的操作,例如向表中添加记录。所以我尝试从 DI 获取 AppDbContext
但它始终为空。请看代码:
public class Scheduler
{
static Timer _timer;
static bool _isStarted;
static ILogger<Scheduler> _logger;
const int dueTimeMin = 1;
const int periodMin = 1;
public static void Start(IServiceProvider serviceProvider)
{
if (_isStarted)
throw new Exception("Currently is started");
_logger = (ILogger<Scheduler>)serviceProvider.GetService(typeof(ILogger<Scheduler>));
var autoEvent = new AutoResetEvent(false);
var operationClass = new OperationClass(serviceProvider);
_timer = new Timer(operationClass.DoOperation, autoEvent, dueTimeMin * 60 * 1000, periodMin * 60 * 1000);
_isStarted = true;
_logger.LogInformation("Scheduler started");
}
}
public class OperationClass
{
IServiceProvider _serviceProvider;
ILogger<OperationClass> _logger;
AppDbContext _appDbContext;
public OperationClass(IServiceProvider serviceProvider)
{
_serviceProvider = serviceProvider;
_logger = (ILogger<OperationClass>)serviceProvider.GetService(typeof(ILogger<OperationClass>));
_appDbContext = (AppDbContext)_serviceProvider.GetService(typeof(AppDbContext));
}
public void DoOperation(Object stateInfo)
{
try
{
_logger.LogInformation("Timer elapsed.");
if (_appDbContext == null)
throw new Exception("appDbContext is null");
_appDbContext.PlayNows.Add(new PlayNow
{
DateTime = DateTime.Now
});
_appDbContext.SaveChanges();
}
catch (Exception exception)
{
_logger.LogError($"Error in DoOperation: {exception.Message}");
}
}
}
这是来自 Startup
的代码:
public Startup(IHostingEnvironment env, IServiceProvider serviceProvider)
{
var builder = new ConfigurationBuilder()
.SetBasePath(env.ContentRootPath)
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
.AddEnvironmentVariables();
Configuration = builder.Build();
AppHelper.InitializeMapper();
Scheduler.Start(serviceProvider);
}
我想我在错误的地方调用了 Scheduler.Start
。似乎 AppDbContext
还没有准备好。
调用 Scheduler.Start
的正确位置是什么?
最佳答案
当您在后台线程上运行代码时,您应该始终在该后台线程上为您的 DI 容器开始一个新的“范围”并从该范围解析。
那么你应该做的是:
- 在事件中创建一个新范围
- 从该范围解析
OperationClass
OperationClass
内部只依赖于构造函数注入(inject);不在Service Location .
您的代码应如下所示:
public class Scheduler
{
static Timer _timer;
const int dueTimeMin = 1;
const int periodMin = 1;
public static void Start(IServiceScopeFactory scopeFactory)
{
if (scopeFactory == null) throw new ArgumentNullException("scopeFactory");
_timer = new Timer(_ =>
{
using (var scope = new scopeFactory.CreateScope())
{
scope.GetRequiredService<OperationClass>().DoOperation();
}
}, new AutoResetEvent(false), dueTimeMin * 60 * 1000, periodMin * 60 * 1000);
}
}
这里Start
依赖于IServiceScopeFactory
。 IServiceScopeFactory
可以从 IServiceProvider
解析。
您的 OperationClass
将变成如下所示:
public class OperationClass
{
private readonly ILogger<OperationClass> _logger;
private readonly AppDbContext _appDbContext;
public OperationClass(ILogger<OperationClass> logger, AppDbContext appDbContext)
{
if (logger == null) throw new ArgumentNullException(nameof(logger));
if (appDbContext == null) throw new ArgumentNullException(nameof(appDbContext));
_logger = logger;
_appDbContext = appDbContext;
}
public void DoOperation()
{
try
{
_logger.LogInformation("DoOperation.");
_appDbContext.PlayNows.Add(new PlayNow
{
DateTime = DateTime.Now
});
_appDbContext.SaveChanges();
}
catch (Exception exception)
{
_logger.LogError($"Error in DoOperation: {exception}");
}
}
}
虽然不是特定于 .NET Core 容器的文档,this documentation提供了有关如何在多线程应用程序中使用 DI 容器的更详细信息。
关于c# - 在 ASP.NET Core 中添加数据库驱动的调度程序的正确位置是什么?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45128033/