Restored hack in GroupedProjection and added support for multi-columns property projection

Author: bahusoid

src/NHibernate.Test/Async/CompositeId/ClassWithCompositeIdFixture.cs

@@ -396,5 +396,17 @@ public async Task QueryOverOrderByAndWhereWithIdProjectionDoesntThrowAsync()
 				Assert.That(results.Count, Is.EqualTo(1));
 			}
 		}
+
+		[Test]
+		public async Task CriteriaGroupProjectionAsync()
+		{
+			using (ISession s = OpenSession())
+			{
+				await (s.CreateCriteria<ClassWithCompositeId>()
+				.SetProjection(Projections.GroupProperty(Projections.Id()))
+				.Add(Restrictions.Eq(Projections.Id(), id))
+				.ListAsync<Id>());
+			}
+		}
 	}
 }

src/NHibernate.Test/CompositeId/ClassWithCompositeIdFixture.cs

@@ -385,5 +385,17 @@ public void QueryOverOrderByAndWhereWithIdProjectionDoesntThrow()
 				Assert.That(results.Count, Is.EqualTo(1));
 			}
 		}
+
+		[Test]
+		public void CriteriaGroupProjection()
+		{
+			using (ISession s = OpenSession())
+			{
+				s.CreateCriteria<ClassWithCompositeId>()
+				.SetProjection(Projections.GroupProperty(Projections.Id()))
+				.Add(Restrictions.Eq(Projections.Id(), id))
+				.List<Id>();
+			}
+		}
 	}
 }

src/NHibernate/Criterion/GroupedProjection.cs

@@ -9,6 +9,7 @@ namespace NHibernate.Criterion
 	public class GroupedProjection : IProjection
 	{
 		private readonly IProjection projection;
+		private SqlString renderedProjection;
 
 		public GroupedProjection(IProjection projection)
 		{
@@ -17,12 +18,16 @@ public GroupedProjection(IProjection projection)
 
 		public virtual SqlString ToSqlString(ICriteria criteria, int position, ICriteriaQuery criteriaQuery)
 		{
-			return projection.ToSqlString(criteria, position, criteriaQuery);
+			return renderedProjection = projection.ToSqlString(criteria, position, criteriaQuery);
 		}
 
 		public virtual SqlString ToGroupSqlString(ICriteria criteria, ICriteriaQuery criteriaQuery)
 		{
-			return SqlStringHelper.Join(new SqlString(","), CriterionUtil.GetColumnNamesAsSqlStringParts(null, projection, criteriaQuery, criteria));
+			if (projection is IPropertyProjection propertyProjection)
+				return new SqlString(string.Join(", ", criteriaQuery.GetColumns(criteria, propertyProjection.PropertyName)));
+
+			//This is kind of a hack. The hack is based on the fact that ToGroupSqlString always called after ToSqlString.
+			return SqlStringHelper.RemoveAsAliasesFromSql(renderedProjection);
 		}
 
 		public virtual IType[] GetTypes(ICriteria criteria, ICriteriaQuery criteriaQuery)