From 37a550a489ec3a8ee9d6f32f647ec275ce966447 Mon Sep 17 00:00:00 2001
From: rbock <rbock@eudoxos.de>
Date: Thu, 24 Jul 2014 09:29:50 +0200
Subject: [PATCH] Use potential outer table dependencies in pseudo tables

The dependency indicates whether a column of a pseudo table can be null.
---
 include/sqlpp11/detail/type_set.h     | 19 ++++++++++++++++++-
 include/sqlpp11/field.h               |  1 +
 include/sqlpp11/select_pseudo_table.h | 10 ++++++----
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/sqlpp11/detail/type_set.h b/include/sqlpp11/detail/type_set.h
index a46ffb9b..1e95cc6a 100644
--- a/include/sqlpp11/detail/type_set.h
+++ b/include/sqlpp11/detail/type_set.h
@@ -204,13 +204,30 @@ namespace sqlpp
 			struct make_difference_set<type_set<Minuends...>, type_set<Subtrahends...>>
 			{
 				template<typename E>
-				using is_subtrahend = is_element_of<E, type_set<Subtrahends...>>;
+					using is_subtrahend = is_element_of<E, type_set<Subtrahends...>>;
 				using type = typename make_type_set_if_not<is_subtrahend, Minuends...>::type;
 			};
 
 		template<typename Minuend, typename Subtrahend>
 			using make_difference_set_t = typename make_difference_set<Minuend, Subtrahend>::type;
 
+		template<typename Lhs, typename Rhs>
+			struct make_intersect_set
+			{
+				static_assert(::sqlpp::wrong_t<Lhs, Rhs>::value, "invalid argument for intersect set");
+			};
+
+		template<typename... LhsElements, typename... RhsElements>
+			struct make_intersect_set<type_set<LhsElements...>, type_set<RhsElements...>>
+			{
+				template<typename E>
+					using is_in_both = is_element_of<E, make_type_set_t<LhsElements..., RhsElements...>>;
+				using type = typename make_type_set_if<is_in_both, LhsElements...>::type;
+			};
+
+		template<typename Lhs, typename Rhs>
+			using make_intersect_set_t = typename make_intersect_set<Lhs, Rhs>::type;
+
 
 		template<template<typename> class Transformation, typename T>
 			struct transform_set
diff --git a/include/sqlpp11/field.h b/include/sqlpp11/field.h
index 1a5db815..02e0a849 100644
--- a/include/sqlpp11/field.h
+++ b/include/sqlpp11/field.h
@@ -48,6 +48,7 @@ namespace sqlpp
 
 	namespace detail
 	{
+#warning: Need to transport the "can be null" information via field_t to result_entry structs
 		template<typename NamedExpr>
 			struct make_field_t_impl
 			{
diff --git a/include/sqlpp11/select_pseudo_table.h b/include/sqlpp11/select_pseudo_table.h
index 60bb9c9b..856845b5 100644
--- a/include/sqlpp11/select_pseudo_table.h
+++ b/include/sqlpp11/select_pseudo_table.h
@@ -32,16 +32,18 @@
 namespace sqlpp
 {
 	// provide type information for sub-selects that are used as named expressions or tables
-	template<typename NamedExpr>
+	template<typename Select, typename NamedExpr>
 		struct select_column_spec_t
 		{
-#warning use Select here to determine if a column relates to a outer join table
 			using _name_t = typename NamedExpr::_name_t;
 
+			static constexpr bool _can_be_null = can_be_null_t<NamedExpr>::value;
+			static constexpr bool _depends_on_outer_table = detail::make_intersect_set_t<required_tables_of<NamedExpr>, typename Select::_used_outer_tables>::size::value > 0;
+
 			using _traits = make_traits<value_type_of<NamedExpr>, 
 						tag::must_not_insert, 
 						tag::must_not_update,
-						typename std::conditional<can_be_null_t<NamedExpr>::value, tag::can_be_null, void>::type
+						typename std::conditional<_can_be_null or _depends_on_outer_table, tag::can_be_null, void>::type
 							>;
 		};
 
@@ -51,7 +53,7 @@ namespace sqlpp
 							 >
 							 struct select_pseudo_table_t: public sqlpp::table_t<select_pseudo_table_t<
 																						 Select,
-																						 NamedExpr...>, select_column_spec_t<NamedExpr>...>
+																						 NamedExpr...>, select_column_spec_t<Select, NamedExpr>...>
 	{
 		using _traits = make_traits<no_value_t, tag::table, tag::pseudo_table>;
 		using _recursive_traits = make_recursive_traits<>;