// file      : odb/traits.hxx
// author    : Boris Kolpackov <boris@codesynthesis.com>
// copyright : Copyright (c) 2009-2011 Code Synthesis Tools CC
// license   : GNU GPL v2; see accompanying LICENSE file

#ifndef ODB_TRAITS_HXX
#define ODB_TRAITS_HXX

#include <odb/pre.hxx>

#include <odb/forward.hxx>
#include <odb/pointer-traits.hxx>

namespace odb
{
  // template <typename T>
  // class access::object_traits;
  //
  // Specializations should define the following members:
  //
  // id_type               - object id (primary key) type
  // id_type id (const T&) - get object id
  //
  // void persist (database&, T&)
  // void update (database&, T&)
  // void erase (database&, const id_type&)
  // pointer_type find (database&, const id_type&)
  // bool find (database&, const id_type&, T&)
  //
  //

  template <typename T, typename P>
  class access::object_factory
  {
  public:
    typedef T object_type;
    typedef P pointer_type;

    static P
    create ()
    {
      // By default use pointer-specific construction.
      //
      return pointer_factory<T, P>::create ();
    }
  };

  template <typename T, typename P>
  class access::pointer_factory
  {
  public:
    typedef T object_type;
    typedef P pointer_type;

    static P
    create ()
    {
      void* v (pointer_traits<P>::allocate (sizeof (T)));
      mem_guard g (v);
      P p (new (v) T);
      g.release ();
      return p;
    }
  private:
    struct mem_guard
    {
      mem_guard (void* p): p_ (p) {}
      ~mem_guard () {if (p_) pointer_traits<P>::free (p_);}
      void release () {p_ = 0;}
      void* p_;
    };
  };

  template <typename T>
  struct object_traits:
    access::object_traits<T>,
    access::object_factory<T, typename access::object_traits<T>::pointer_type>
  {
    //
    // If a C++ compiler issues an error pointing to this struct and
    // saying that it is incomplete, then you are most likely trying to
    // perform a database operation on a C++ type that is not a persistent
    // object. Or you forgot to include the corresponding -odb.hxx file.
    //

    typedef
    odb::pointer_traits<typename access::object_traits<T>::pointer_type>
    pointer_traits;

    typedef typename access::object_traits<T>::object_type object_type;
    typedef typename access::object_traits<T>::pointer_type pointer_type;
    typedef typename pointer_traits::const_pointer_type const_pointer_type;
  };

  // Specialization for const objects. It only defines the id, object,
  // pointer, and const_pointer types with pointer and const_pointer
  // being the same. The idea is to only use this specialization in the
  // interfaces, with the implementations detecting this situation and
  // using the non-const object_traits version.
  //
  template <typename T>
  struct object_traits<const T>
  {
  private:
    typedef
    odb::pointer_traits<typename access::object_traits<T>::pointer_type>
    pointer_traits;

  public:
    typedef typename access::object_traits<T>::id_type id_type;
    typedef typename access::object_traits<T>::object_type object_type;
    typedef typename pointer_traits::const_pointer_type const_pointer_type;
    typedef const_pointer_type pointer_type;
  };

  // Specializations for pointer types to allow the C++ compiler to
  // instantiate persist(), etc., signatures in class database. The
  // overloads that use these specializations would never actually
  // be selected by the compiler.
  //
  template <typename T>
  struct object_traits<T*>
  {
    struct id_type {};
  };

  template <typename T>
  struct object_traits<T* const>
  {
    struct id_type {};
  };

  template <typename T, template <typename> class P>
  struct object_traits< P<T> >
  {
    struct id_type {};
  };

  template <typename T, template <typename> class P>
  struct object_traits< const P<T> >
  {
    struct id_type {};
  };

  template <typename T>
  struct composite_value_traits: access::composite_value_traits<T>
  {
  };
}

#include <odb/post.hxx>

#endif // ODB_TRAITS_HXX