From 2f586daf18e4d3b15e1b96576d85f7090163bb2d Mon Sep 17 00:00:00 2001
From: "sangwan.kwon" <sangwan.kwon@samsung.com>
Date: Tue, 16 Jan 2018 16:22:42 +0900
Subject: [PATCH] Support DISTINCT constraint on select clause

Change-Id: I562cd17bf2b6a1f8be7f66ce0678214735224c6b
Signed-off-by: sangwan.kwon <sangwan.kwon@samsung.com>
---
 include/klay/db/query-builder/column.hxx    | 11 ++++++++
 include/klay/db/query-builder/table.hxx     | 28 +++++++++++++++++++--
 include/klay/db/query-builder/test-main.cpp |  3 +++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/klay/db/query-builder/column.hxx b/include/klay/db/query-builder/column.hxx
index d24ae73..0a58869 100644
--- a/include/klay/db/query-builder/column.hxx
+++ b/include/klay/db/query-builder/column.hxx
@@ -18,4 +18,15 @@ Column<O, F> make_column(const std::string& name, F O::*field) {
 	return {name, field};
 }
 
+template<typename Type>
+struct Distinct {
+	Type value;
+};
+
+template<typename... Args>
+auto distinct(Args&&... args) -> decltype(Distinct<std::tuple<Args...>>())
+{
+	return {std::make_tuple(std::forward<Args>(args)...)};
+}
+
 } // namespace qxx
diff --git a/include/klay/db/query-builder/table.hxx b/include/klay/db/query-builder/table.hxx
index 8e2829e..cc81ef4 100644
--- a/include/klay/db/query-builder/table.hxx
+++ b/include/klay/db/query-builder/table.hxx
@@ -20,6 +20,9 @@ public:
 	template<typename... ColumnTypes>
 	Self select(ColumnTypes&&... cts);
 
+	template<typename Type>
+	Self select(Distinct<Type> distinct);
+
 	Self selectAll(void);
 
 	template<typename... ColumnTypes>
@@ -44,6 +47,9 @@ private:
 	template<typename ...Cs>
 	friend Table<Cs...> make_table(const std::string& name, Cs&& ...columns);
 
+	template<typename ColumnTuple>
+	Self selectInternal(ColumnTuple&& ct, bool distinct = false);
+
 	template<typename Cs>
 	std::vector<std::string> getColumnNames(Cs&& tuple);
 
@@ -97,15 +103,33 @@ Table<Columns...>::Table(const std::string& name, ImplType impl)
 template<typename... Columns>
 template<typename... ColumnTypes>
 Table<Columns...> Table<Columns...>::select(ColumnTypes&&... cts)
+{
+	auto columnTuple = std::make_tuple(std::forward<ColumnTypes>(cts)...);
+
+	return this->selectInternal(std::move(columnTuple));
+}
+
+template<typename... Columns>
+template<typename Type>
+Table<Columns...> Table<Columns...>::select(Distinct<Type> distinct)
+{
+	return this->selectInternal(std::move(distinct.value), true);
+}
+
+template<typename... Columns>
+template<typename ColumnTuple>
+Table<Columns...> Table<Columns...>::selectInternal(ColumnTuple&& ct, bool distinct)
 {
 	this->cache.clear();
 
-	auto columnTuple = std::make_tuple(std::forward<ColumnTypes>(cts)...);
-	auto columnNames = this->getColumnNames(std::move(columnTuple));
+	auto columnNames = this->getColumnNames(std::move(ct));
 
 	std::stringstream ss;
 	ss << "SELECT ";
 
+	if (distinct)
+		ss << "DISTINCT ";
+
 	for (const auto& c : columnNames)
 		ss << c << " ";
 
diff --git a/include/klay/db/query-builder/test-main.cpp b/include/klay/db/query-builder/test-main.cpp
index b6842e7..ee13df2 100644
--- a/include/klay/db/query-builder/test-main.cpp
+++ b/include/klay/db/query-builder/test-main.cpp
@@ -30,6 +30,8 @@ int main() {
 												  expr(&Admin::pkg) == "dpm");
 	std::string select6 = admin.selectAll().where(expr(&Admin::uid) > 3 ||
 												  expr(&Admin::pkg) == "dpm");
+	std::string select7 = admin.select(distinct(&Admin::uid, &Admin::key))
+							   .where(expr(&Admin::id) > 3);
 
 	std::cout << select1 << '\n'; // SELECT id pkg uid key FROM admin
 	std::cout << select2 << '\n'; // SELECT id uid key FROM admin
@@ -37,6 +39,7 @@ int main() {
 	std::cout << select4 << '\n'; // SELECT * FROM admin WHERE uid = ?
 	std::cout << select5 << '\n'; // SELECT * FROM admin WHERE uid = ? AND pkg = ?
 	std::cout << select6 << '\n'; // SELECT * FROM admin WHERE uid = ? OR pkg = ?
+	std::cout << select7 << '\n'; // SELECT DISTINCT uid key FROM admin WHERE id = ?
 
 	int uid = 0, id = 1;
 	std::string update1 = admin.update(&Admin::id, &Admin::pkg, &Admin::uid, &Admin::key);
-- 
2.34.1