Prevent creating objects with duplicated GUIDs

src/SIL.LCModel/LcmGenerate/factory.vm.cs

@@ -64,7 +64,19 @@ internal partial class ${className}$classSfx : I${className}$classSfx, ILcmFacto
 			if (m_cache.ServiceLocator.GetInstance<I${className}Repository>().Singleton != null)
 				throw new InvalidOperationException("Can not create more than one ${className}");
 #end
-			if (guid == Guid.Empty) guid = Guid.NewGuid();
+			if (guid == Guid.Empty)
+			{
+				guid = Guid.NewGuid();
+			}
+			else
+			{
+				if (m_cache.ServiceLocator.GetInstance<ICmObjectRepository>().IsValidObjectId(guid))
+				{
+					// IsValidObjectId returns true if the GUID exists, i.e. you could call GetObject and get something.
+					// But here in Create(), it's an error if the GUID already exists: duplicate GUIDs are not allowed.
+					throw new InvalidOperationException("Can not create more than one object with identical GUIDs");
+				}
+			}
 			int hvo = m_cache.InternalServices.DataReader.GetNextRealHvo();
 			var newby = new $className(m_cache, hvo, guid);
 #if ( $ownerStatus != "required")

tests/SIL.LCModel.Tests/DomainImpl/FactoryAdditionsTests.cs

@@ -1,7 +1,8 @@
-// Copyright (c) 2015 SIL International
+// Copyright (c) 2015 SIL International
 // This software is licensed under the LGPL, version 2.1 or later
 // (http://www.gnu.org/licenses/lgpl-2.1.html)
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using NUnit.Framework;
@@ -132,5 +133,28 @@ public void LexSenseFactoryCreate_NullGlossTss_DoesNotThrow()
 			Assert.DoesNotThrow(() => sense = lexSenseFactory.Create(entry, msa, nullGloss));
 			Assert.AreEqual(0, sense.Gloss.StringCount);
 		}
+
+		[Test]
+		public void Create_WithDuplicateGuid_SameType_Throws()
+		{
+			var guid = Guid.NewGuid();
+			var factory = Cache.ServiceLocator.GetInstance<ILexEntryFactory>();
+			factory.Create(guid);
+
+			Assert.That(() => factory.Create(guid),
+				Throws.TypeOf<InvalidOperationException>().With.Message.Contains("identical GUIDs"));
+		}
+
+		[Test]
+		public void Create_WithDuplicateGuid_DifferentType_Throws()
+		{
+			var guid = Guid.NewGuid();
+			var entryFactory = Cache.ServiceLocator.GetInstance<ILexEntryFactory>();
+			entryFactory.Create(guid);
+
+			var pictureFactory = Cache.ServiceLocator.GetInstance<ICmPictureFactory>();
+			Assert.That(() => pictureFactory.Create(guid),
+				Throws.TypeOf<InvalidOperationException>().With.Message.Contains("identical GUIDs"));
+		}
 	}
 }