From ad515f85e807f8d21a1b70f5ed288705e0f2f531 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 1 Oct 2015 11:50:21 +0200
Subject: Add helper header for nested container emulation

Still fairly experimental, only supports vector<vector<T>>.
---
 odb/nested-container.hxx | 115 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 odb/nested-container.hxx

diff --git a/odb/nested-container.hxx b/odb/nested-container.hxx
new file mode 100644
index 0000000..a4cf564
--- /dev/null
+++ b/odb/nested-container.hxx
@@ -0,0 +1,115 @@
+// file      : odb/nested-container.hxx
+// copyright : Copyright (c) 2009-2015 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+#ifndef ODB_NESTED_CONTAINER_HXX
+#define ODB_NESTED_CONTAINER_HXX
+
+#include <odb/pre.hxx>
+
+#include <cstddef> // size_t
+
+#include <odb/forward.hxx>
+#include <odb/details/config.hxx> // ODB_CXX11
+
+#ifndef ODB_CXX11
+#  error nested container support is only available in C++11
+#endif
+
+namespace odb
+{
+  // Nested container emulation support for ODB.
+  //
+  // Note that the outer key in the inner container should strictly
+  // speaking be a foreign key pointing to the key of the outer
+  // container. The only way to achieve this currently is to manually
+  // add the constraint via ALTER TABLE ADD CONSTRAINT. Note, however,
+  // that as long as we only modify these tables via the ODB container
+  // interface, not having the foreign key (and not having ON DELETE
+  // CASCADE) should be harmless (since we have a foreign key pointing
+  // to the object id).
+  //
+
+  // Map key that is used to emulate nested container mapping in ODB.
+  // Template parameter T is a tag that allows us to distinguish keys
+  // for unrelated containers in order to assign column names, etc.
+  // Use inner container type for T.
+  //
+  template <typename T,
+            typename O = std::size_t,
+            typename I = std::size_t>
+  struct nested_key
+  {
+    using outer_type = O;
+    using inner_type = I;
+
+    outer_type outer;
+    inner_type inner;
+
+    nested_key () = default;
+    nested_key (outer_type o, inner_type i): outer (o), inner (i) {}
+
+    bool
+    operator< (const nested_key& v) const
+    {
+      return outer < v.outer || (outer == v.outer && inner < v.inner);
+    }
+  };
+}
+
+#include <map>
+#include <vector>
+#include <cstddef>     // size_t
+#include <utility>     // move(), declval()
+#include <cassert>
+#include <type_traits> // remove_reference
+
+namespace odb
+{
+  // vector<vector<>>
+  //
+  template <typename IC>
+  struct nested_value_type:
+    std::remove_reference<decltype (std::declval<IC> ()[0])> {};
+
+  template <typename IC>
+  std::map<nested_key<IC>, typename nested_value_type<IC>::type>
+  nested_get (const std::vector<IC>& v)
+  {
+    using namespace std;
+
+    using I = typename nested_value_type<IC>::type;
+    using K = nested_key<IC>;
+
+    map<K, I> r;
+    for (size_t n (0); n != v.size (); ++n)
+    {
+      const IC& o (v[n]);
+      for (size_t m (0); m != o.size (); ++m)
+        r.emplace (K (n, m), o[m]);
+    }
+    return r;
+  }
+
+  template <typename K, typename I, typename IC>
+  void
+  nested_set (std::vector<IC>& v, std::map<K, I>&& r)
+  {
+    using namespace std;
+
+    for (auto& p: r)
+    {
+      size_t n (p.first.outer);
+      size_t m (p.first.inner);
+      I& i (p.second);
+
+      assert (n < v.size ());
+      assert (m == v[n].size ());
+      v[n].push_back (move (i));
+    }
+  }
+}
+
+#include <odb/post.hxx>
+
+#endif // ODB_NESTED_CONTAINER_HXX
-- 
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