c# - DbContext 实例同时在两个地方使用 - EF - Hangfire

Question

我正在使用 EF Core 和 Hangfire运行重复性作业。 Hangfire 似乎导致了以下错误:

A second operation started on this context before a previous operationcompleted. This is usually caused by different threads using the sameinstance of DbContext. For more information on how to avoid threadingissues with DbContext

而且..我不确定为什么。我按如下方式注册 EF 上下文:

services 
    .AddDbContext<PaymentContext>(options => options.UseNpgsql(connectionString),
    ServiceLifetime.Transient); 

然后..

app.UseHangfireDashboard();
app.UseHangfireServer();
   
RecurringJob.AddOrUpdate(() => myService.ExecuteMyJob(), Cron.Minutely);

其中 myService 已注入(inject) Startup.Configure 函数，并且 myService 包含对 DbContext 的引用。这在理论上是暂时的，因此不应由服务和其他地方共享。

但是堆栈跟踪引导到这里:

var plans = _context.Plan
                .Include(pp => pp.PlanItem)
                .Where(pp => pp.PolicyId == policyId)
                .ToList() // materialise query
                .OrderBy(pp => pp.PlanItem.First().Date)
                .ToList();

Answer 1

您应该为您的依赖创建作用域。

public class Job
{
    private readonly IServiceProvider _serviceProvider;
    
    public Job(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    public void ExecuteJob()
    {
        using (var scope = serviceProvider.CreateScope())
        {
            var databaseContext = scope.ServiceProvider.GetRequiredService<DatabaseContext>();
            // do something
        }
    }
}