Fix MappingByCode discriminator string type throws (#3126)

Fixes #2717

Author: bahusoid

src/NHibernate.Test/Async/NHSpecificTest/GH2717/DiscriminatorStringTypeByCodeFixture.cs

@@ -0,0 +1,74 @@
+//------------------------------------------------------------------------------
+// <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.Linq;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+using NHibernate.Linq;
+
+namespace NHibernate.Test.NHSpecificTest.GH2717
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class DiscriminatorStringTypeByCodeFixtureAsync : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Entity>(rc =>
+			{
+				rc.Id(x => x.Id, m => m.Generator(Generators.GuidComb));
+				rc.Discriminator(x => x.Type(NHibernateUtil.String));
+				rc.Property(x => x.Name);
+				rc.Abstract(true);
+			});
+			mapper.Subclass<Subclass>(rc => rc.DiscriminatorValue("xxx"));
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var e1 = new Subclass { Name = "Bob" };
+				session.Save(e1);
+
+				transaction.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				session.CreateQuery("delete from System.Object").ExecuteUpdate();
+				transaction.Commit();
+			}
+		}
+
+		[Test]
+		public async Task QueryOnSubclassWithStringDiscriminatorAsync()
+		{
+			using (var session = OpenSession())
+			{
+				var result = await ((from e in session.Query<Subclass>()
+							  where e.Name == "Bob"
+							  select e)
+							  .ToListAsync());
+
+				Assert.That(result.Count, Is.EqualTo(1));
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2717/DiscriminatorStringTypeByCodeFixture.cs

@@ -0,0 +1,62 @@
+using System.Linq;
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH2717
+{
+	[TestFixture]
+	public class DiscriminatorStringTypeByCodeFixture : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Entity>(rc =>
+			{
+				rc.Id(x => x.Id, m => m.Generator(Generators.GuidComb));
+				rc.Discriminator(x => x.Type(NHibernateUtil.String));
+				rc.Property(x => x.Name);
+				rc.Abstract(true);
+			});
+			mapper.Subclass<Subclass>(rc => rc.DiscriminatorValue("xxx"));
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override void OnSetUp()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				var e1 = new Subclass { Name = "Bob" };
+				session.Save(e1);
+
+				transaction.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				session.CreateQuery("delete from System.Object").ExecuteUpdate();
+				transaction.Commit();
+			}
+		}
+
+		[Test]
+		public void QueryOnSubclassWithStringDiscriminator()
+		{
+			using (var session = OpenSession())
+			{
+				var result = (from e in session.Query<Subclass>()
+							  where e.Name == "Bob"
+							  select e)
+							  .ToList();
+
+				Assert.That(result.Count, Is.EqualTo(1));
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2717/Entity.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH2717
+{
+	class Entity
+	{
+		public virtual Guid Id { get; set; }
+		public virtual string Name { get; set; }
+	}
+
+	class Subclass : Entity
+	{
+	}
+}

src/NHibernate/Mapping/ByCode/Impl/DiscriminatorMapper.cs

@@ -57,15 +57,15 @@ public void Column(Action<IColumnMapper> columnMapper)
 
 		public void Type(IType persistentType)
 		{
-			if (persistentType != null)
-			{
-				discriminatorMapping.type = persistentType.Name;
-			}
+			if (persistentType is not IDiscriminatorType discriminatorType)
+				throw new ArgumentOutOfRangeException(nameof(persistentType), "Expected type implementing " + nameof(IDiscriminatorType));
+
+			Type(discriminatorType);
 		}
 
 		public void Type(IDiscriminatorType persistentType)
 		{
-			Type(persistentType.GetType());
+			discriminatorMapping.type = persistentType.Name;
 		}
 
 		public void Type<TPersistentType>() where TPersistentType : IDiscriminatorType
@@ -142,4 +142,4 @@ private void ResetColumnPlainValues()
 			discriminatorMapping.formula = null;
 		}
 	}
-}
+}