Adding limitation for EFCore with multiple DbCommandInterceptor (#164)

* Adding limitation for EFCore with multiple DbCommandInterceptor

* Adding doc ref for AsyncLocal

Author: srprash

README.md

@@ -395,6 +395,8 @@ For how to start with Entity Framework Core in an ASP.NET Core web app, please t
 * You need to install `AWSXRayRecorder.Handlers.EntityFramework` nuget package. This package adds extension methods to the `DbContextOptionsBuilder` to make it easy to register AWS X-Ray interceptor.
 * Not all database provider support Entity Framework Core 3.0 and above, please make sure that you are using the [Nuget package](https://docs.microsoft.com/en-us/ef/core/providers/?tabs=dotnet-core-cli) with a compatible version (EF Core >= 3.0).
 
+*Known Limitation (as of 12-03-2020):* If you're using another `DbCommandInterceptor` implementation along with the `AddXRayInterceptor` in the `DbContext`, it may not work as expected and you may see a "EntityNotAvailableException" from the XRay EFCore interceptor. This is due to [`AsyncLocal`](https://docs.microsoft.com/en-us/dotnet/api/system.threading.asynclocal-1?view=netcore-2.0) not being able to maintain context across the `ReaderExecutingAsync` and `ReaderExecutedAsync` methods. Ref [here](https://github.com/dotnet/efcore/issues/22766) for more details on the issue.
+
 #### Setup
 
 In order to trace SQL query, you can register your `DbContext` with `AddXRayInterceptor()` accordingly in the `ConfigureServices` method in `startup.cs` file.