nhibernateGH-3530: Many drivers lack support for the DbDataReader.Get…

…Char method. Add a NoCharDbDataReader to use with these drivers.

src/NHibernate/AdoNet/NoCharDbDataReader.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Data.Common;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace NHibernate.AdoNet
+{
+	/// <summary>
+	/// Many database drivers lack support for DbDataReader.GetChar and throw a
+	/// NotSupportedException. This reader provides an implementation on top of
+	/// the indexer method for defficient drivers.
+	/// </summary>
+	public class NoCharDbDataReader : DbDataReaderWrapper
+	{
+		public NoCharDbDataReader(DbDataReader reader) : base(reader) { }
+
+		public override char GetChar(int ordinal)
+		{
+			// The underlying DataReader does not support the GetChar method.
+			// Use the indexer to obtain the value and convert it to a char if necessary.
+			var value = DataReader[ordinal];
+
+			return value switch
+			{
+				string { Length: > 0 } s => s[0],
+				_ => (char) value
+			};
+		}
+	}
+}