Fix limits in polymorphic queries (#2618)

Results from the query should be skipped if they are already in the
ISet distinction thus if distinction.Add is false. Currently, they are
only added if they have been there before.

Fixes #2614

Author: csharper2010

src/NHibernate.Test/Async/NHSpecificTest/GH2614/Fixture.cs

@@ -0,0 +1,54 @@
+//------------------------------------------------------------------------------
+// <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 NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH2614
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class FixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using (var s = OpenSession())
+			using (var t = s.BeginTransaction())
+			{
+				s.Save(new ConcreteClass1 {Name = "C1"});
+				s.Save(new ConcreteClass2 {Name = "C2"});
+				t.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var s = OpenSession())
+			using (var t = s.BeginTransaction())
+			{
+				s.CreateQuery("delete from System.Object").ExecuteUpdate();
+				t.Commit();
+			}
+		}
+
+		[Test]
+		public async Task PolymorphicListReturnsCorrectResultsAsync()
+		{
+			using (var s = OpenSession())
+			using (s.BeginTransaction())
+			{
+				var query = s.CreateQuery(
+					@"SELECT Name FROM NHibernate.Test.NHSpecificTest.GH2614.BaseClass ROOT");
+				query.SetMaxResults(5);
+				var list = await (query.ListAsync());
+				Assert.That(list.Count, Is.EqualTo(2));
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2614/BaseClass.cs

@@ -0,0 +1,8 @@
+namespace NHibernate.Test.NHSpecificTest.GH2614
+{
+	public abstract class BaseClass
+	{
+		public virtual int Id { get; set; }
+		public virtual string Name { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2614/ConcreteClass1.cs

@@ -0,0 +1,6 @@
+namespace NHibernate.Test.NHSpecificTest.GH2614
+{
+	public class ConcreteClass1 : BaseClass
+	{
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2614/ConcreteClass2.cs

@@ -0,0 +1,8 @@
+using System.Collections.Generic;
+
+namespace NHibernate.Test.NHSpecificTest.GH2614
+{
+	public class ConcreteClass2 : BaseClass
+	{
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2614/Fixture.cs

@@ -0,0 +1,43 @@
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH2614
+{
+	[TestFixture]
+	public class Fixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using (var s = OpenSession())
+			using (var t = s.BeginTransaction())
+			{
+				s.Save(new ConcreteClass1 {Name = "C1"});
+				s.Save(new ConcreteClass2 {Name = "C2"});
+				t.Commit();
+			}
+		}
+
+		protected override void OnTearDown()
+		{
+			using (var s = OpenSession())
+			using (var t = s.BeginTransaction())
+			{
+				s.CreateQuery("delete from System.Object").ExecuteUpdate();
+				t.Commit();
+			}
+		}
+
+		[Test]
+		public void PolymorphicListReturnsCorrectResults()
+		{
+			using (var s = OpenSession())
+			using (s.BeginTransaction())
+			{
+				var query = s.CreateQuery(
+					@"SELECT Name FROM NHibernate.Test.NHSpecificTest.GH2614.BaseClass ROOT");
+				query.SetMaxResults(5);
+				var list = query.List();
+				Assert.That(list.Count, Is.EqualTo(2));
+			}
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2614/Mappings.hbm.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
+           namespace="NHibernate.Test.NHSpecificTest.GH2614"
+           assembly="NHibernate.Test"
+>
+  <class name="ConcreteClass1" >
+    <id name="Id">
+      <generator class="increment"/>
+    </id>
+    <property name="Name"/>
+  </class>
+
+  <class name="ConcreteClass2" >
+    <id name="Id">
+      <generator class="increment"/>
+    </id>
+    <property name="Name"/>
+  </class>
+
+</hibernate-mapping>

src/NHibernate/Async/Engine/Query/HQLQueryPlan.cs

@@ -78,7 +78,7 @@ public async Task PerformListAsync(QueryParameters queryParameters, ISessionImpl
 					for (int x = 0; x < size; x++)
 					{
 						object result = tmp[x];
-						if (distinction.Add(result))
+						if (!distinction.Add(result))
 						{
 							continue;
 						}

src/NHibernate/Engine/Query/HQLQueryPlan.cs

@@ -128,7 +128,7 @@ public void PerformList(QueryParameters queryParameters, ISessionImplementor ses
 					for (int x = 0; x < size; x++)
 					{
 						object result = tmp[x];
-						if (distinction.Add(result))
+						if (!distinction.Add(result))
 						{
 							continue;
 						}