NH-3609 - Fixed issue where Avg with Conditional inside would generate invalid sql.

Author: hazzik

src/NHibernate.Test/NHSpecificTest/NH3609/Fixture.cs

@@ -35,6 +35,28 @@ protected override void OnTearDown()
 			}
 		}
 
+		[Test]
+		public void AvgWithConditionalDoesNotThrow()
+		{
+			using (var session = OpenSession())
+			using (session.BeginTransaction())
+			{
+				MappingEntity mappingEntity = null;
+				Assert.DoesNotThrow(
+					() =>
+						session.QueryOver<Entity>().SelectList(
+							builder =>
+								builder.Select(
+									Projections.Avg(
+										Projections.Conditional(
+											Restrictions.Eq(Projections.Property<Entity>(x => x.Name), "FOO"),
+											Projections.Constant("", NHibernateUtil.String),
+											Projections.Constant(null, NHibernateUtil.String))).WithAlias(() => mappingEntity.Count))
+						).TransformUsing(Transformers.AliasToBean<MappingEntity>()).List<MappingEntity>()
+					);
+			}
+		}
+
 		[Test]
 		public void CountWithConditionalDoesNotThrow()
 		{

src/NHibernate/Criterion/AvgProjection.cs

@@ -12,32 +12,32 @@ namespace NHibernate.Criterion
 	public class AvgProjection : AggregateProjection
 	{
 		public AvgProjection(IProjection projection) : base("avg", projection) {}
-		public AvgProjection(String propertyName) : base("avg", propertyName) {}
+		public AvgProjection(string propertyName) : base("avg", propertyName) {}
 
-		public override SqlString ToSqlString(ICriteria criteria, int loc, ICriteriaQuery criteriaQuery,
-		                                      IDictionary<string, IFilter> enabledFilters)
+		public override SqlString ToSqlString(ICriteria criteria, int loc, ICriteriaQuery criteriaQuery, IDictionary<string, IFilter> enabledFilters)
 		{
 			ISessionFactoryImplementor factory = criteriaQuery.Factory;
 			SqlType[] sqlTypeCodes = NHibernateUtil.Double.SqlTypes(factory);
 			string sqlType = factory.Dialect.GetCastTypeName(sqlTypeCodes[0]);
-			string parameter;
+
+			var sql = new SqlStringBuilder().Add(aggregate).Add("(");
+			sql.Add("cast(");
 			if (projection != null)
 			{
-				parameter =
-					SqlStringHelper.RemoveAsAliasesFromSql(projection.ToSqlString(criteria, loc, criteriaQuery, enabledFilters)).ToString();
+				sql.Add(SqlStringHelper.RemoveAsAliasesFromSql(projection.ToSqlString(criteria, loc, criteriaQuery, enabledFilters)));
 			}
 			else
 			{
-				parameter = criteriaQuery.GetColumn(criteria, propertyName);
+				sql.Add(criteriaQuery.GetColumn(criteria, propertyName));
 			}
-			string expression = string.Format("{0}(cast({1} as {2})) as {3}", aggregate, parameter, sqlType,
-			                                  GetColumnAliases(loc, criteria, criteriaQuery)[0]);
-			return new SqlString(expression);
+			sql.Add(" as ").Add(sqlType).Add(")");
+			sql.Add(") as ").Add(GetColumnAliases(loc, criteria, criteriaQuery)[0]);
+			return sql.ToSqlString();
 		}
 
 		public override IType[] GetTypes(ICriteria criteria, ICriteriaQuery criteriaQuery)
 		{
 			return new IType[] {NHibernateUtil.Double};
 		}
 	}
-}
+}