nhibernateGH-3530: The MySql driver doesn't properly convert strings …

…from the database to decimal types. Add a MySqlDbDataReader to correct this deficiency.

src/NHibernate/AdoNet/MySqlDbDataReader.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using System.Data.Common;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace NHibernate.AdoNet
+{
+	public class MySqlDbDataReader : DbDataReaderWrapper
+	{
+		public MySqlDbDataReader(DbDataReader reader) : base(reader) { }
+
+		// MySql driver has a bug that incorrectly uses the CurrentCulture to parse strings.
+		public override float GetFloat(int ordinal)
+		{
+			var value = DataReader[ordinal];
+
+			return value switch
+			{
+				string => Convert.ToSingle(value, CultureInfo.InvariantCulture),
+				_ => (float) value
+			};
+		}
+
+		public override double GetDouble(int ordinal)
+		{
+			var value = DataReader[ordinal];
+
+			return value switch
+			{
+				string => Convert.ToDouble(value, CultureInfo.InvariantCulture),
+				_ => (double) value
+			};
+		}
+
+		public override decimal GetDecimal(int ordinal)
+		{
+			var value = DataReader[ordinal];
+
+			return value switch
+			{
+				string => Convert.ToDecimal(value, CultureInfo.InvariantCulture),
+				_ => (decimal) value
+			};
+		}
+	}
+}

src/NHibernate/Async/Driver/MySqlDataDriver.cs

@@ -0,0 +1,30 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using System;
+using System.Data.Common;
+using NHibernate.AdoNet;
+
+namespace NHibernate.Driver
+{
+	using System.Threading.Tasks;
+	using System.Threading;
+	public partial class MySqlDataDriver : ReflectionBasedDriver, IEmbeddedBatcherFactoryProvider
+	{
+
+		public override async Task<DbDataReader> ExecuteReaderAsync(DbCommand command, CancellationToken cancellationToken)
+		{
+			cancellationToken.ThrowIfCancellationRequested();
+			var reader = await (command.ExecuteReaderAsync(cancellationToken)).ConfigureAwait(false);
+
+			return new MySqlDbDataReader(reader);
+		}
+	}
+}

src/NHibernate/Driver/MySqlDataDriver.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Data.Common;
 using NHibernate.AdoNet;
 
 namespace NHibernate.Driver
@@ -17,7 +18,7 @@ namespace NHibernate.Driver
 	/// for any updates and/or documentation regarding MySQL.
 	/// </para>
 	/// </remarks>
-	public class MySqlDataDriver : ReflectionBasedDriver, IEmbeddedBatcherFactoryProvider
+	public partial class MySqlDataDriver : ReflectionBasedDriver, IEmbeddedBatcherFactoryProvider
 	{
 		/// <summary>
 		/// Initializes a new instance of the <see cref="MySqlDataDriver"/> class.
@@ -79,6 +80,13 @@ public override IResultSetsCommand GetResultSetsCommand(Engine.ISessionImplement
 		/// <inheritdoc />
 		public override DateTime MinDate => new DateTime(1000, 1, 1);
 
+		public override DbDataReader ExecuteReader(DbCommand command)
+		{
+			var reader = command.ExecuteReader();
+
+			return new MySqlDbDataReader(reader);
+		}
+
 		System.Type IEmbeddedBatcherFactoryProvider.BatcherFactoryClass => typeof(MySqlClientBatchingBatcherFactory);
 	}
 }