DBPointer.h

/**************************************************************************
 * BASF2 (Belle Analysis Framework 2)                                     *
 * Copyright(C) 2016 - Belle II Collaboration                             *
 *                                                                        *
 * Author: The Belle II Collaboration                                     *
 * Contributors: Thomas Kuhr                                              *
 *                                                                        *
 * This software is provided "as is" without any warranty.                *
 **************************************************************************/
#pragma once
 
#include <framework/database/DBArray.h>
 
namespace Belle2 {
  std::string DBPointer_defaultName = "";
 
  template<class T, typename KEY, KEY(T::*METHOD)() const, const std::string& NAME = DBPointer_defaultName> class DBPointer {
  public:
 
    explicit DBPointer(KEY key):
      m_key(key), m_object(0) {};
 
    inline KEY key() const {return m_key;}
 
    inline operator KEY() const {return m_key;}
 
    inline KEY operator = (KEY key) {m_key = key; m_object = 0; return m_key;}
 
    inline bool isValid() const {return getPointer();}
 
    inline operator bool() const {return isValid();}
 
    inline const T& operator *()  const {return *getPointer();}  
    inline const T* operator ->() const {return getPointer();}   
  private:
    inline const T* getPointer() const
    {
      if (!m_object) {
        DBArray<T> array(NAME);
        m_object = array.getByKey(METHOD, m_key);
      }
      return m_object;
    }
 
    KEY m_key;
 
    mutable const T* m_object;   
  };
}