"There is already an open DataReader associated with this Connection..." on .Include()

The issue

I’m trying to load multiple pieces of data, and my second piece of data is dependent on the first piece of data. Basically I don’t know whether I need to load the second piece of data, before I retrieved the first piece of data.

Here’s an example:

// First piece of data
var frontPageSettings = _context.Settings.FirstOrDefault(x => x.Key == Constants.SettingsKeys.FrontPageSettings.ToString());
if (frontPageSettings != null && frontPageSettings.ShowFeaturedThreads)
{
    var threads = _context.Threads.Include(x => x.UserProfile).Where(x => x.IsFeatured).OrderByDescending(x => x.FeatureDate).Take(3).ToList();
}

If I remove the .Include(x=> x.UserProfile) I’m not getting any exceptions, so I believe that’s the source of the problem.

This creates the following exception:

Exception message: There is already an open DataReader associated with this Connection which must be closed first.
Stack trace:
   at MySql.Data.MySqlClient.MySqlCommand.VerifyValid()
   at MySql.Data.MySqlClient.CommandExecutors.TextCommandExecutor.<ExecuteReaderAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MySql.Data.MySqlClient.CommandExecutors.TextCommandExecutor.<ExecuteNonQueryAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MySql.Data.MySqlClient.MySqlCommand.<ExecuteNonQueryAsync>d__46.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery()
   at MySql.Data.MySqlClient.MySqlTransaction.Dispose(Boolean disposing)
   at Microsoft.EntityFrameworkCore.Storage.Internal.MySqlRelationalTransaction.Dispose()
   at Microsoft.EntityFrameworkCore.Query.QueryMethodProvider.<_Include>d__30`1.System.IDisposable.Dispose()
   at Microsoft.EntityFrameworkCore.Query.QueryMethodProvider.<_Include>d__30`1.MoveNext()
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.<_TrackEntities>d__15`2.MoveNext()
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at OurGhostsOfWar.Controllers.HomeController.Index()

Further technical details

Pomelo.EntityFrameworkCore.MySql version: 1.1.1-prerelease-10017

Other details about my project setup: I’m using MAriaDB instead of MySQL, but that’s just a simple fork of MySQL. Shouldn’t cause any problems problems, and haven’t the during the last year I’ve been working with MariaDB and the Pomelo.EntityFrameworkCore.MySql package provider

[caleblloyd]

I’ll look into the incorrect exception. It comes because the reader hasn’t been used due to the first exception, then the transaction getting closed throws the DataReader exception. We need to make sure the first exception gets through though.

[detilium]

Found my issue.

I’m not sure why it’s giving me the exception: There is already an open DataReader associated with this Connection which must be closed first., when the actual problem is an InvalidCastException.

I had a datatype of BLOB in my DB, but in my class i defined the property as a string. It tried to cast a byte[] into a string, hence the invalid cast exception.

Thank you for you help anyways, at least I got my package updated 👍 I hope I didn’t take to much of your time 😉