Merge pull request #541 from jforage/issue-U4-5758

Fix to issue U4-5758. Branched off from 7.2.0

src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs

@@ -369,6 +369,7 @@ AND umbracoNode.id <> @id",
             }
 
             var sortOrder = 1;
+			var newAlias = 0;
 
 			foreach (var pre in values)
 			{
@@ -389,9 +390,24 @@ AND umbracoNode.id <> @id",
 				}
 				else
 				{
+					// adding new prevalue so make sure our alias is unique by adding 1 to the largest existing (or newly added already within this batch)
+					if (newAlias > 0)
+					{
+						newAlias++;
+					}
+					else
+					{
+						newAlias =
+							Database.ExecuteScalar<int>(
+								"SELECT (coalesce(max(alias), 0) + 1) " +
+								"FROM cmsDataTypePreValues " +
+								"WHERE datatypeNodeId = @datatypeNodeId",
+								new { datatypeNodeId = dataType.Id });
+					}
+
 					_preValRepository.AddOrUpdate(new PreValueEntity
 					{
-                        Alias = pre.Key,
+						Alias = Convert.ToString(newAlias),
 						SortOrder = sortOrder,
 						Value = pre.Value.Value,
 						DataType = dataType,