From 980daac5178ac712a49aa106f3d20db444fa608e Mon Sep 17 00:00:00 2001
From: Roland Bock <rbock@eudoxos.de>
Date: Fri, 25 Oct 2024 07:31:56 +0200
Subject: [PATCH] Implement CTE alias (allowing self-join)

---
 include/sqlpp11/core/clause/cte.h    | 60 +++++++++++++++++++++++-----
 tests/core/serialize/clause/from.cpp |  9 +++++
 2 files changed, 59 insertions(+), 10 deletions(-)

diff --git a/include/sqlpp11/core/clause/cte.h b/include/sqlpp11/core/clause/cte.h
index 01ec9733..dd75ea7f 100644
--- a/include/sqlpp11/core/clause/cte.h
+++ b/include/sqlpp11/core/clause/cte.h
@@ -134,6 +134,40 @@ namespace sqlpp
     using type = member_t<FieldSpec, column_t<cte_ref_t<NameTagProvider>, FieldSpec>>;
   };
 
+#warning: Need to document that you need to be a bit careful with aliased CTEs as we use cte_ref in columns, from, and join.
+  template <typename NameTagProvider, typename NewNameTagProvider, typename... FieldSpecs>
+  struct cte_as_t : public cte_member<NewNameTagProvider, FieldSpecs>::type...,
+                 public enable_join<cte_as_t<NameTagProvider, NewNameTagProvider, FieldSpecs...>>
+  {
+  };
+
+  template <typename NameTagProvider, typename NewNameTagProvider, typename... ColumnSpecs>
+  struct is_table<cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>> : public std::true_type
+  {
+  };
+
+  template <typename NameTagProvider, typename NewNameTagProvider, typename... ColumnSpecs>
+  struct name_tag_of<cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>> : public name_tag_of<NewNameTagProvider>
+  {
+  };
+
+  template <typename NameTagProvider, typename NewNameTagProvider, typename... ColumnSpecs>
+    struct provided_tables_of<cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>> 
+    {
+      using type = sqlpp::detail::type_vector<cte_ref_t<NewNameTagProvider>>;
+    };
+
+  template <typename NameTagProvider, typename NewNameTagProvider, typename... ColumnSpecs>
+    struct provided_static_tables_of<cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>> : public provided_tables_of<cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>>
+    {
+    };
+
+  template <typename Context, typename NameTagProvider, typename NewNameTagProvider, typename... ColumnSpecs>
+  auto to_sql_string(Context& context, const cte_as_t<NameTagProvider, NewNameTagProvider, ColumnSpecs...>&) -> std::string
+  {
+    return name_to_sql_string(context, name_tag_of_t<NameTagProvider>::name) + " AS " + name_to_sql_string(context, name_tag_of_t<NewNameTagProvider>::name);
+  }
+
   template <typename NameTagProvider, typename Statement, typename... FieldSpecs>
   struct cte_t : public cte_member<NameTagProvider, FieldSpecs>::type...,
                  public enable_join<cte_t<NameTagProvider, Statement, FieldSpecs...>>
@@ -151,6 +185,13 @@ namespace sqlpp
 
     using _result_row_t = result_row_t<void, FieldSpecs...>;
 
+    template <typename NewNameTagProvider>
+    constexpr auto as(const NewNameTagProvider& /*unused*/) const
+        -> cte_as_t<NameTagProvider, NewNameTagProvider, FieldSpecs...>
+    {
+      return {};
+    }
+
     template <typename Rhs>
     auto union_distinct(Rhs rhs) const
         -> union_cte_impl_t<check_cte_union_t<Rhs>,
@@ -205,7 +246,7 @@ namespace sqlpp
     Statement _statement;
   };
 
-#warning: is table? really?
+#warning: is table? really? cte_ref needs to be a table, not sure about cte_t
   template <typename NameTagProvider, typename Statement, typename... ColumnSpecs>
   struct is_table<cte_t<NameTagProvider, Statement, ColumnSpecs...>> : public std::true_type
   {
@@ -219,13 +260,12 @@ namespace sqlpp
   template <typename Context, typename NameTagProvider, typename Statement, typename... ColumnSpecs>
   auto to_sql_string(Context& context, const cte_t<NameTagProvider, Statement, ColumnSpecs...>& t) -> std::string
   {
-    return name_to_sql_string(context, name_tag_of_t<NameTagProvider>::name) +  " AS (" + 
-    to_sql_string(context, t._statement) + ")";
+    return name_to_sql_string(context, name_tag_of_t<NameTagProvider>::name) + " AS (" +
+           to_sql_string(context, t._statement) + ")";
   }
 
-  // The cte_t is displayed as NameTagProviderName except within the with:
-  //    - the with needs the
-  //      NameTagProviderName AS (ColumnNames) (select/union)
+  // The cte_ref_t represents the cte as table in FROM.
+  // The cte_t needs to be provided by WITH.
   template <typename NameTagProvider>
   struct cte_ref_t
   {
@@ -247,10 +287,13 @@ namespace sqlpp
     }
   };
 
-#warning: is table? really?
    template<typename NameTagProvider>
     struct is_table<cte_ref_t<NameTagProvider>> : public std::true_type{};
 
+   template<typename NameTagProvider>
+    struct name_tag_of<cte_ref_t<NameTagProvider>> : public name_tag_of<NameTagProvider>
+    {};
+
    template<typename NameTagProvider>
     struct provided_tables_of<cte_ref_t<NameTagProvider>> 
     {
@@ -262,9 +305,6 @@ namespace sqlpp
     {
     };
 
-   template<typename NameTagProvider>
-    struct name_tag_of<cte_ref_t<NameTagProvider>> : public name_tag_of<NameTagProvider>{};
-
   template <typename Context, typename NameTagProvider>
   auto to_sql_string(Context& context, const cte_ref_t<NameTagProvider>&) -> std::string
   {
diff --git a/tests/core/serialize/clause/from.cpp b/tests/core/serialize/clause/from.cpp
index f39eb871..fe70d9db 100644
--- a/tests/core/serialize/clause/from.cpp
+++ b/tests/core/serialize/clause/from.cpp
@@ -36,6 +36,9 @@ int main()
   const auto cFoo = foo.as(sqlpp::alias::c);
 
   const auto x = cte(sqlpp::alias::x).as(select(foo.id).from(foo).unconditionally());
+  const auto xa = x.as(sqlpp::alias::a);
+  const auto xb = x.as(sqlpp::alias::b);
+  const auto y = cte(sqlpp::alias::y).as(select(foo.id).from(foo).unconditionally());
 
   // Single table
   SQLPP_COMPARE(from(foo), " FROM tab_foo");
@@ -53,7 +56,13 @@ int main()
 
   // CTE
   SQLPP_COMPARE(from(x), " FROM x");
+  SQLPP_COMPARE(from(foo.join(x).on(x.id == foo.id)), " FROM tab_foo INNER JOIN x ON x.id = tab_foo.id");
   SQLPP_COMPARE(from(x.join(foo).on(x.id == foo.id)), " FROM x INNER JOIN tab_foo ON x.id = tab_foo.id");
+  SQLPP_COMPARE(from(x.join(y).on(x.id == y.id)), " FROM x INNER JOIN y ON x.id = y.id");
+#warning: Some of these should go into CTE tests
+  SQLPP_COMPARE(xa, "x AS a");
+  SQLPP_COMPARE(xa.id == xb.id, "a.id = b.id");
+  SQLPP_COMPARE(from(xa.join(xb).on(xa.id == xb.id)), " FROM x AS a INNER JOIN x AS b ON a.id = b.id");
 
 #warning add tests for dynamic joins