我需要从此类访问上下文,以便可以检查数据库中的某些数据,但是我不知道如何将其传输到以下服务:
internal class TimedHostedService : IHostedService, IDisposable
{
private readonly ILogger _logger;
private Timer _timer;
public TimedHostedService(ILogger<TimedHostedService> logger) //context ?
{
_logger = logger;
}
public Task StartAsync(CancellationToken cancellationToken)
{
_logger.LogInformation("Timed Background Service is starting.");
_timer = new Timer(DoWork, null, TimeSpan.Zero,
TimeSpan.FromSeconds(60));
return Task.CompletedTask;
}
private void DoWork(object state)
{
_logger.LogInformation("Atualização automática");
}
public Task StopAsync(CancellationToken cancellationToken)
{
_logger.LogInformation("Timed Background Service is stopping.");
_timer?.Change(Timeout.Infinite, 0);
return Task.CompletedTask;
}
public void Dispose()
{
_timer?.Dispose();
}
}
启动文件:
namespace Products
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddCors(o => o.AddPolicy("AllowAllOrigins", builder =>
{
builder.AllowAnyMethod()
.AllowAnyHeader()
.AllowAnyOrigin();
}));
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
services.AddDbContext<Context>(options =>
options.UseSqlServer(Configuration.GetConnectionString("LaprDB")));
services.AddDbContext<ContextUsers>(options =>
options.UseSqlServer(Configuration.GetConnectionString("MyDbConnection")));
services.AddHostedService<TimedHostedService>();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseHsts();
}
app.UseCors("AllowAllOrigins");
app.UseHttpsRedirection();
app.UseMvc();
}
}
}
我在范围内的工厂中搜索了一些解决方案,但我听不懂。有人可以向我解释如何将上下文传输到TimedHostedService吗? 如果您需要更多信息,请告诉我。
答案 0 :(得分:2)
托管服务是单例,这意味着在应用程序的生命周期中仅存在该类的一个实例。
上下文是有作用域的,这意味着它的使用寿命很短(仅适用于特定的“范围”,例如单个HTTP请求)。无限期地保持生命状态不好(例如,涉及数据库连接,您无法保证在应用程序的生命周期内保持打开状态)。
如果将Context注入另一个类,则该Context在该类实例的生命周期内将一直存在。对于单例类,这就是应用程序的生命。所以这就是为什么您会得到例外的原因。 .NET Core告诉您:“这不会像您认为的那样工作”
解决方案在这里:https://stackoverflow.com/a/48368934/1202807
简而言之,注入一个IServiceScopeFactory
,它使您能够在需要时让DI引擎为您提供作用域类,然后由您决定是否将其保留在附近需要它。
private readonly IServiceScopeFactory _scopeFactory;
public TimedHostedService(ILogger<TimedHostedService> logger, IServiceScopeFactory scopeFactory)
{
_logger = logger;
_scopeFactory = scopeFactory;
}
然后您会得到这样的上下文:
using (var scope = scopeFactory.CreateScope())
{
var context = scope.ServiceProvider.GetRequiredService<Context>();
//do what you need
}//scope (and context) gets destroyed here
旧答案(这里是错误的,但适用于其他类型的类):
只需将其放入构造函数中,它将被dependency injection注入:
public TimedHostedService(ILogger<TimedHostedService> logger, Context context)
{
_logger = logger;
_context = context;
}
services.AddDbContext()
行使它们可用于依赖项注入。既然已经定义了两个,就选择您想要的类型:
services.AddDbContext<Context>(options =>
options.UseSqlServer(Configuration.GetConnectionString("LaprDB")));
services.AddDbContext<ContextUsers>(options =>
options.UseSqlServer(Configuration.GetConnectionString("MyDbConnection")));