Prevent creating objects with duplicated GUIDs (#367)

* Check before creating an object; if an object with the same GUID exists, throw
* Add tests
* Fix exception message (the rule is global across all types)

Fixes #365.

This should not affect FW, since the FooFactory.Create(guid) method is not used in FieldWorks. FW Lite uses it, so that FW Lite can create LCM objects with GUIDs that match the GUIDs of objects that are being synchronized from other projects. And FW Lite will be changed to expect an InvalidOperationError to be thrown in case of a duplicated GUID being created, and handle the resulting merge conflict accordingly.

---------

Co-authored-by: Tim Haasdyk <tim_haasdyk@sil.org>

Author: rmunn

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"));
+		}
 	}
 }