Added value_or_null method/type

include/sqlpp11/boolean.h

@@ -39,7 +39,7 @@ namespace sqlpp
 	// boolean value type
 	struct boolean
 	{
-		using _traits = make_traits<boolean, ::sqlpp::tag::is_boolean, ::sqlpp::tag::is_expression>;
+		using _traits = make_traits<boolean, ::sqlpp::tag::is_boolean, ::sqlpp::tag::is_value_type>;
 		using _tag = ::sqlpp::tag::is_boolean;
 		using _cpp_value_type = bool;
 

include/sqlpp11/floating_point.h

@@ -38,7 +38,7 @@ namespace sqlpp
 	// floating_point value type
 	struct floating_point
 	{
-		using _traits = make_traits<floating_point, ::sqlpp::tag::is_floating_point, ::sqlpp::tag::is_expression>;
+		using _traits = make_traits<floating_point, ::sqlpp::tag::is_floating_point, ::sqlpp::tag::is_value_type>;
 		using _tag = ::sqlpp::tag::is_floating_point;
 		using _cpp_value_type = double;
 

include/sqlpp11/functions.h

@@ -42,10 +42,10 @@
 #include <sqlpp11/avg.h>
 #include <sqlpp11/sum.h>
 #include <sqlpp11/verbatim_table.h> // Csaba Csoma suggests: unsafe_sql instead of verbatim
+#include <sqlpp11/value_or_null.h>
 
 namespace sqlpp
 {
-#warning add a value_or_null method that yields a type that can be NULL or have a value (very similar to an optional)
 #warning add a template<typename Db> bool_expression which takes any bool expression as constructor argument
 	template<typename T>
 		auto value(T t) -> wrap_operand_t<T>
@@ -101,6 +101,18 @@ namespace sqlpp
 			return { context.str() };
 		}
 
+	template<typename Expression>
+		auto is_null(Expression e) -> decltype(e.is_null())
+		{
+			return e.is_null();
+		}
+
+	template<typename Expression>
+		auto is_not_null(Expression e) -> decltype(e.is_not_null())
+		{
+			return e.is_not_null();
+		}
+
 	template<typename Container>
 		struct value_list_t // to be used in .in() method
 		{

include/sqlpp11/integral.h

@@ -40,7 +40,7 @@ namespace sqlpp
 	// integral value type
 	struct integral
 	{
-		using _traits = make_traits<integral, ::sqlpp::tag::is_integral, ::sqlpp::tag::is_expression>;
+		using _traits = make_traits<integral, ::sqlpp::tag::is_integral, ::sqlpp::tag::is_value_type>;
 		using _tag = ::sqlpp::tag::is_integral;
 		using _cpp_value_type = int64_t;
 

include/sqlpp11/null.h

@@ -33,7 +33,7 @@ namespace sqlpp
 {
 	struct null_t
 	{
-		using _traits = make_traits<no_value_t, tag::is_expression>;
+		using _traits = make_traits<no_value_t, tag::is_expression, tag::is_sql_null>;
 		using _recursive_traits = make_recursive_traits<>;
 	};
 

include/sqlpp11/parameter.h

@@ -83,7 +83,7 @@ namespace sqlpp
 		auto parameter(const ValueType&, const AliasProvider&)
 		-> parameter_t<wrap_operand_t<ValueType>, AliasProvider>
 		{
-			static_assert(is_expression_t<ValueType>::value, "first argument is not a value type");
+			static_assert(is_value_type_t<ValueType>::value, "first argument is not a value type");
 			static_assert(is_alias_provider_t<AliasProvider>::value, "second argument is not an alias provider");
 			return {};
 		}

include/sqlpp11/text.h

@@ -39,7 +39,7 @@ namespace sqlpp
 	// text value type
 	struct text
 	{
-		using _traits = make_traits<text, ::sqlpp::tag::is_text, ::sqlpp::tag::is_expression>;
+		using _traits = make_traits<text, ::sqlpp::tag::is_text, ::sqlpp::tag::is_value_type>;
 		using _tag = ::sqlpp::tag::is_text;
 		using _cpp_value_type = std::string;
 

include/sqlpp11/type_traits.h

@@ -71,6 +71,8 @@ namespace sqlpp
 	template<typename T>\
 	using name##_t = typename detail::name##_impl<T>::type;
 
+	SQLPP_VALUE_TRAIT_GENERATOR(is_value_type);
+	SQLPP_VALUE_TRAIT_GENERATOR(is_sql_null);
 	SQLPP_VALUE_TRAIT_GENERATOR(is_boolean);
 	SQLPP_VALUE_TRAIT_GENERATOR(is_integral);
 	SQLPP_VALUE_TRAIT_GENERATOR(is_floating_point);

include/sqlpp11/value_or_null.h

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2013-2014, Roland Bock
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ * 
+ *   Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ * 
+ *   Redistributions in binary form must reproduce the above copyright notice, this
+ *   list of conditions and the following disclaimer in the documentation and/or
+ *   other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef SQLPP_VALUE_OR_NULL_H
+#define SQLPP_VALUE_OR_NULL_H
+
+#include <sqlpp11/parameter.h>
+#include <sqlpp11/parameter_list.h>
+#include <sqlpp11/column_types.h>
+#include <sqlpp11/in.h>
+#include <sqlpp11/value_type.h>
+#include <sqlpp11/exists.h>
+#include <sqlpp11/any.h>
+#include <sqlpp11/some.h>
+#include <sqlpp11/count.h>
+#include <sqlpp11/min.h>
+#include <sqlpp11/max.h>
+#include <sqlpp11/avg.h>
+#include <sqlpp11/sum.h>
+#include <sqlpp11/verbatim_table.h> // Csaba Csoma suggests: unsafe_sql instead of verbatim
+#include <sqlpp11/value_or_null.h>
+
+namespace sqlpp
+{
+	template<typename ValueType>
+		struct value_or_null_t
+		{
+			using _cpp_value_type = typename ValueType::_cpp_value_type;
+
+			using _traits = make_traits<ValueType, tag::is_expression>;
+			using _recursive_traits = make_recursive_traits<>;
+
+			value_or_null_t(_cpp_value_type value):
+				_value(value),
+				_is_null(false)
+			{}
+
+			value_or_null_t(const null_t&):
+				_value(),
+				_is_null(true)
+				{}
+
+			typename ValueType::_cpp_value_type _value;
+			bool _is_null;
+		};
+
+	template<typename T>
+		auto value_or_null(T t) -> value_or_null_t<value_type_of<wrap_operand_t<T>>>
+		{
+			static_assert(is_wrapped_value_t<wrap_operand_t<T>>::value, "value_or_null() is to be called with non-sql-type like int, or string or null");
+			return { t };
+		}
+
+	template<typename ValueType>
+		auto value_or_null(null_t t) -> value_or_null_t<ValueType>
+		{
+			static_assert(is_value_type_t<ValueType>::value, "value_or_null() is to be called with non-sql-type like int, or string");
+			return { t };
+		}
+
+}
+
+#endif

tests/FunctionTest.cpp

@@ -135,6 +135,12 @@ int main()
 		using TI = decltype(t.alpha.is_null());
 		using TF = decltype(f.omega.is_null());
 		using TT = decltype(t.beta.is_null());
+		using TTI = decltype(is_null(t.alpha));
+		using TTF = decltype(is_null(f.omega));
+		using TTT = decltype(is_null(t.beta));
+		static_assert(std::is_same<TI, TTI>::value, "type requirement");
+		static_assert(std::is_same<TF, TTF>::value, "type requirement");
+		static_assert(std::is_same<TT, TTT>::value, "type requirement");
 		static_assert(sqlpp::is_named_expression_t<TI>::value, "type requirement");
 		static_assert(sqlpp::is_boolean_t<TI>::value, "type requirement");
 		static_assert(not sqlpp::is_numeric_t<TI>::value, "type requirement");
@@ -154,6 +160,12 @@ int main()
 		using TI = decltype(t.alpha.is_not_null());
 		using TF = decltype(f.omega.is_not_null());
 		using TT = decltype(t.beta.is_not_null());
+		using TTI = decltype(is_not_null(t.alpha));
+		using TTF = decltype(is_not_null(f.omega));
+		using TTT = decltype(is_not_null(t.beta));
+		static_assert(std::is_same<TI, TTI>::value, "type requirement");
+		static_assert(std::is_same<TF, TTF>::value, "type requirement");
+		static_assert(std::is_same<TT, TTT>::value, "type requirement");
 		static_assert(sqlpp::is_named_expression_t<TI>::value, "type requirement");
 		static_assert(sqlpp::is_boolean_t<TI>::value, "type requirement");
 		static_assert(not sqlpp::is_numeric_t<TI>::value, "type requirement");
@@ -356,6 +368,30 @@ int main()
 		static_assert(sqlpp::is_text_t<TT>::value, "type requirement");
 	}
 
+	// test value_or_null
+	{
+		using TB = decltype(sqlpp::value_or_null(true));
+		using TI = decltype(sqlpp::value_or_null(7));
+		using TF = decltype(sqlpp::value_or_null(5.6));
+		using TT = decltype(sqlpp::value_or_null("hallo"));
+		using TBN = decltype(sqlpp::value_or_null<sqlpp::boolean>(sqlpp::null));
+		using TIN = decltype(sqlpp::value_or_null<sqlpp::integral>(sqlpp::null));
+		using TFN = decltype(sqlpp::value_or_null<sqlpp::floating_point>(sqlpp::null));
+		using TTN = decltype(sqlpp::value_or_null<sqlpp::text>(sqlpp::null));
+		static_assert(std::is_same<TB, TBN>::value, "type_requirement");
+		static_assert(std::is_same<TI, TIN>::value, "type_requirement");
+		static_assert(std::is_same<TF, TFN>::value, "type_requirement");
+		static_assert(std::is_same<TT, TTN>::value, "type_requirement");
+		static_assert(not sqlpp::is_named_expression_t<TB>::value, "type requirement");
+		static_assert(sqlpp::is_boolean_t<TB>::value, "type requirement");
+		static_assert(not sqlpp::is_named_expression_t<TB>::value, "type requirement");
+		static_assert(sqlpp::is_integral_t<TI>::value, "type requirement");
+		static_assert(not sqlpp::is_named_expression_t<TI>::value, "type requirement");
+		static_assert(sqlpp::is_floating_point_t<TF>::value, "type requirement");
+		static_assert(not sqlpp::is_named_expression_t<TT>::value, "type requirement");
+		static_assert(sqlpp::is_text_t<TT>::value, "type requirement");
+	}
+
 	// test verbatim
 	{
 		using TB = decltype(sqlpp::verbatim<sqlpp::boolean>("1"));