usage_upcasting.txt

LiteSQL is a C++ library that integrates C++ objects tightly to relational database and thus provide

/* LiteSQL - Documentation 
 * 
 * By Tero Laitinen 
 * 
 * See LICENSE for copyright information. */
/* \file usage_upcasting.txt
    Manual */

/** \page usage_upcasting Upcasting and Virtual Methods

In order to support virtual methods a Persistent object must be upcasted to
correct type before calling virtual method.

upcast is a template method to which you must pass a correct base type of 
Persistent. upcast will return an auto_ptr which holds a pointer to an object
of correct type.

upcastCopy is similar to upcast. It does not select an object of correct type
but just constructs it in memory. Note that constructed object does not have
all of its fields. This method is suitable when virtual method to be called
does not need any special fields.

An example of upcast:
\code
Playable pl = select<Playable>(db).one();
pl.upcast()->play();
\endcode

An another example of upcast:
\code
Playable pl = select<Playable>(db).one();
auto_ptr<Playable> uc = pl.upcast();
cout << "Playing " << uc->name << endl;
uc->play();
\endcode

An example of upcastCopy:
\code
Playable pl = select<Playable>(db).one();
pl.upcastCopy()->makeLogEntry(log);
\endcode
*/