Allow columns index be shared between columns from base and subclass classes

Fixes #2099

Author: bahusoid

src/NHibernate.Test/NHSpecificTest/GH2099/Entity.cs

@@ -0,0 +1,26 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH2099
+{
+	abstract class PersistentObject
+	{
+		public virtual Guid Id { get; set; }
+		public virtual bool PDO_Deleted { get; set; }
+	}
+
+	class WorkflowInstance : PersistentObject
+	{
+		public virtual bool IsWaiting { get; set; }
+	}
+	
+	class Level3 : WorkflowInstance
+	{
+		public virtual bool IsActive { get; set; }
+	}
+	
+	class WorkflowInstance2 : PersistentObject
+	{
+		public virtual bool IsActive { get; set; }
+		public virtual bool IsWaiting { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2099/Fixture.cs

@@ -0,0 +1,27 @@
+using System.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH2099
+{
+	[TestFixture]
+	public class Fixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+		}
+
+		protected override void OnTearDown()
+		{
+		}
+
+		[Test]
+		public void BaseClassCanShareIndexNameWithSubclass()
+		{
+			var table = cfg.CreateMappings().IterateTables.FirstOrDefault(t => t.Name == "Level3");
+
+			var index = table.GetIndex("CF_BASE_IDX");
+			Assert.That(index?.ColumnSpan, Is.EqualTo(3));
+			Assert.That(index.ColumnIterator.FirstOrDefault(c => c.Name == "PDO_Deleted"), Is.Not.Null);
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH2099/Mappings.hbm.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernate.Test"
+                   namespace="NHibernate.Test.NHSpecificTest.GH2099">
+
+  <class name="PersistentObject" table="PObject" abstract="true" dynamic-update="true" lazy="true">
+    <id name="Id" generator="guid.comb" />
+    <property name="PDO_Deleted" column="PDO_Deleted" index="IDX_DELETED, CF_BASE_IDX" />
+  </class>
+  
+  <union-subclass name="WorkflowInstance" table="WInstance" abstract="false" dynamic-update="true" lazy="true" extends="PersistentObject">
+    <property name="IsWaiting" column="IsWaiting" index="CF_BASE_IDX" />
+  </union-subclass>
+
+  <union-subclass name="WorkflowInstance2" table="WInstance2" abstract="false" dynamic-update="true" lazy="true" extends="PersistentObject">
+    <property name="IsActive" column="IsActive" index="CF_BASE_IDX" />
+    <property name="IsWaiting" column="IsWaiting" index="CF_BASE_IDX" />
+  </union-subclass>
+
+  <union-subclass name="Level3" table="Level3" abstract="false" dynamic-update="true" lazy="true" extends="WorkflowInstance">
+    <property name="IsActive" column="IsActive" index="CF_BASE_IDX" />
+  </union-subclass>
+</hibernate-mapping>

src/NHibernate/Mapping/DenormalizedTable.cs

@@ -43,8 +43,16 @@ public override IEnumerable<Index> IndexIterator
 				IEnumerable<Index> includedIdxs = includedTable.IndexIterator;
 				foreach (Index parentIndex in includedIdxs)
 				{
+					var sharedIndex = GetIndex(parentIndex.Name);
+					if (sharedIndex != null)
+					{
+						sharedIndex.AddColumns(parentIndex.ColumnIterator);
+						sharedIndex.IsInherited = true;
+						continue;
+					}
 					Index index = new Index();
-					index.Name = Name + parentIndex.Name;
+					index.Name = parentIndex.Name;
+					index.IsInherited = true;
 					index.Table = this;
 					index.AddColumns(parentIndex.ColumnIterator);
 					indexes.Add(index);

src/NHibernate/Mapping/Index.cs

@@ -68,7 +68,8 @@ public static string BuildSqlDropIndexString(Dialect.Dialect dialect, Table tabl
 		/// </returns>
 		public string SqlCreateString(Dialect.Dialect dialect, IMapping p, string defaultCatalog, string defaultSchema)
 		{
-			return BuildSqlCreateIndexString(dialect, Name, Table, ColumnIterator, false, defaultCatalog, defaultSchema);
+			var indexName = IsInherited ? Table.Name + Name : Name;
+			return BuildSqlCreateIndexString(dialect, indexName, Table, ColumnIterator, false, defaultCatalog, defaultSchema);
 		}
 
 		/// <summary>
@@ -144,6 +145,11 @@ public string Name
 			set { name = value; }
 		}
 
+		/// <summary>
+		/// Is this index inherited from the base class mapping 
+		/// </summary>
+		public bool IsInherited { get; set; }
+
 		public bool ContainsColumn(Column column)
 		{
 			return columns.Contains(column);