检测 Entity Framework Core 中的延迟加载

Question

Entity Framework Core 3.1.2 - 我已启用UseLazyLoadingProxies以DbContext确保数据完整性，但如果使用它，我想在开发过程中引发异常。

如何在每次 EF Core 延迟加载关系时执行一些代码？

Answer 1

我知道的唯一方法是诊断消息。请参阅此处的示例： https: //www.domstamand.com/getting-feedback-from-entityframework-core-through-diagnostics。

您想要的事件类是https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.diagnostics.lazyloadingeventdata。

在应用程序的 DBContext 中

#if DEBUG
    static ApplicationDbContext()
    {
        // In DEBUG mode we throw an InvalidOperationException
        // when the app tries to lazy load data.
        // In production we just let it happen, for data
        // consistency reasons.
        DiagnosticListener.AllListeners.Subscribe(new DbContextDiagnosticObserver());
    }
#endif

然后是一个挂钩 EF 通知的类

internal class DbContextDiagnosticObserver : IObserver<DiagnosticListener>
    {
        private readonly DbContextLazyLoadObserver LazyLoadObserver =
            new DbContextLazyLoadObserver();

        public void OnCompleted() { }

        public void OnError(Exception error) { }

        public void OnNext(DiagnosticListener listener)
        {
            if (listener.Name == DbLoggerCategory.Name)
                listener.Subscribe(LazyLoadObserver);
        }
    }

最后是每当发生延迟加载时抛出异常的类

internal class DbContextLazyLoadObserver : IObserver<KeyValuePair<string, object>>
    {
        public void OnCompleted() { }
        public void OnError(Exception error) { }

        public void OnNext(KeyValuePair<string, object> @event)
        {
            // If we see some Lazy Loading, it means the developer needs to
            // fix their code!
            if (@event.Key.Contains("LazyLoading"))
                throw new InvalidOperationException(@event.Value.ToString());
        }
    }

Answer 2

我用它来逐步摆脱代码库中惰性代理的使用：

if (enableProxies)
{
    builder.UseLazyLoadingProxies();
    var lazyLoadEvents = new[]
    {
        CoreEventId.NavigationLazyLoading,
        CoreEventId.DetachedLazyLoadingWarning,
        CoreEventId.LazyLoadOnDisposedContextWarning,
    };
#if DEBUG
    builder.ConfigureWarnings(w => w.Throw(lazyLoadEvents));  //Lazyload now throws in DEBUG
#else
    if (sp.GetService<IHostEnvironment>()?.IsEnvironment("PRD") ?? false)
    {   //logs LazyLoad events as error everywhere else
        builder.ConfigureWarnings(w => w.Log(lazyLoadEvents.Select(lle => (lle, LogLevel.Error)).ToArray())); 
    }
#endif
}

这使得以下内容。在生产中行为没有改变。在 DEBUG 中，使用延迟加载时会引发异常。在资格环境中，会记录错误。