Add missing possible breaking change

releasenotes.txt

@@ -1,3 +1,11 @@
+Build 5.2.1
+=============================
+
+Release notes - NHibernate - Version 5.2.1
+
+As part of releasing 5.2.1, a missing 5.2.0 possible breaking change has been added about duplicated columns
+in mapping. See 5.2.0 possible breaking changes.
+
 Build 5.2.0
 =============================
 
@@ -6,6 +14,11 @@ Release notes - NHibernate - Version 5.2.0
 157 issues were resolved in this release.
 
     ##### Possible Breaking Changes #####
+        * Entities having many non-readonly properties (including many-to-one) mapped to
+          the same column will no more silently ignore the trouble till an insert or update
+          is attempted. They will now cause the session factory built to fail. When
+          mapping many properties to the same column, all of them excepted at most one
+          should be mapped with `insert="false" update="false"`.
         * Mappings mixing column elements and formula elements were taking into account
           only the formula elements. They will now take into account all elements.
         * Mappings mixing column elements and/or formula elements with a column attribute

src/NHibernate.Test/NHSpecificTest/GH1875/Fixture.cs

@@ -12,10 +12,18 @@ public class BadlyMappedEntity
 		public virtual long SecondValue { get; set; }
 	}
 
+	public class EntityWithReadOnlyPropertiesDuplicatingColumns
+	{
+		public virtual Guid Id { get; set; }
+		public virtual Guid IdCopy { get; set; }
+		// Just to "emulate" a pseudo one-to-one while not actually having another entity to map.
+		public virtual EntityWithReadOnlyPropertiesDuplicatingColumns Self { get; set; }
+	}
+
 	[TestFixture]
 	public class Fixture
 	{
-		protected HbmMapping GetMappings()
+		protected HbmMapping GetBadMappings()
 		{
 			var mapper = new ModelMapper();
 			mapper.Class<BadlyMappedEntity>(
@@ -42,7 +50,7 @@ protected HbmMapping GetMappings()
 		[Test]
 		public void ShouldThrowSoundErrorForBadlyMappedEntity()
 		{
-			var mappings = GetMappings();
+			var mappings = GetBadMappings();
 			var cfg = TestConfigurationHelper.GetDefaultConfiguration();
 			cfg.AddMapping(mappings);
 
@@ -59,5 +67,60 @@ public void ShouldThrowSoundErrorForBadlyMappedEntity()
 				factory?.Dispose();
 			}
 		}
+
+		protected HbmMapping GetValidMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<EntityWithReadOnlyPropertiesDuplicatingColumns>(
+				ca =>
+				{
+					ca.Abstract(true);
+					ca.Id(
+						x => x.Id,
+						map =>
+						{
+							map.Column("EntityId");
+							map.Generator(Generators.GuidComb);
+						});
+					ca.ManyToOne(
+						x => x.Self,
+						map =>
+						{
+							map.Column("EntityId");
+							map.Update(false);
+							map.Insert(false);
+						});
+					ca.Property(
+						x => x.IdCopy,
+						map =>
+						{
+							map.Column("EntityId");
+							map.Update(false);
+							map.Insert(false);
+						});
+				});
+
+			return mapper.CompileMappingFor(new[] { typeof(BadlyMappedEntity) });
+		}
+
+		[Test]
+		public void ShouldAcceptReadOnlyPropertiesDuplicatingAColumn()
+		{
+			var mappings = GetValidMappings();
+			var cfg = TestConfigurationHelper.GetDefaultConfiguration();
+			cfg.AddMapping(mappings);
+
+			ISessionFactory factory = null;
+			try
+			{
+				Assert.That(
+					() => factory = cfg.BuildSessionFactory(),
+					Throws.Nothing);
+			}
+			finally
+			{
+				factory?.Dispose();
+			}
+		}
 	}
 }