ASP.NET Core后台任务

濮书
2023-12-01

之前在控制台程序中学习如何运行后台任务,ASP.NET Core中其实也有同样的方法BackgroundService,本以为跟HostedService没有区别,毕竟BackgroundService是继承HostedService的,但实际使用中才发现,依赖注入时,还是有区别的,下面就来说说具体踩到的坑

在服务实现类中,直接注入EF的话,运行时会报错,查了stackoverflow后知道,这里不能直接注入EFContext是因为生命周期问题,BackgroundService是asp.net core开始到结束,而EFContext注入的生命周期是Scoped,在同一个Scope内只初始化一个实例 ,可以理解为( 每一个request级别只创建一个实例,同一个http request会在一个 scope内),所以在启动时,会提示我们把EFContext改为单例注入
所以,代码需要修改成这样

public class DBHostedService : BackgroundService
{
    private readonly ILogger _logger;
    private readonly IServiceScopeFactory _scopeFactory;

    public DBHostedService(ILogger<DBHostedService> logger, IServiceScopeFactory scopeFactory)
    {
        _logger = logger;
        _scopeFactory = scopeFactory;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using (var scope = _scopeFactory.CreateScope())
        {
            var _context = scope.ServiceProvider.GetRequiredService<EFContext>();
            await _context.Database.EnsureDeletedAsync();
            if (await _context.Database.EnsureCreatedAsync())
            {
                if (!_context.QuartInfo.Any())
                {
                    var goodList = new List<QuartzInfo>()
                        {
                            new QuartzInfo(){
                                guid = Guid.NewGuid().ToString(),
                                triggerGroup = "TestGroup1",
                                triggerName = "TestName",
                                cronExpression = "0 0/1 * * * ? ",
                                fullClassName = "BackgroundServiceDemo.TestJob",
                                jobGroup = "jobGroup1",
                                jobName = "jobName1",
                            },
                        };
                    _context.QuartInfo.AddRange(goodList);
                    await _context.SaveChangesAsync();
                }
            }
        }
    }
}

参考资料:
ASP.NET Core 2.1 : 十一. 如何在后台运行一个任务
How should I inject a DbContext instance into an IHostedService

转载于:https://www.cnblogs.com/kw13202/p/10703346.html

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