Re: [Boost-users] [Serialization] Serialize base and derived classes.

Subject: Re: [Boost-users] [Serialization] Serialize base and derived classes.
From: BlueAngel (lists_at_[hidden])
Date: 2010-07-28 06:38:19

Il 26/07/2010 18:58, BlueAngel ha scritto:
> Hi lists,
> I'm working with the Serialization library but I'm having some 
> troubles with it.
> The tutorials in the website shown me much but still I need help.
>
> I'm using XML archives.
> I have this classes actually (these classes are all 
> builders/prototypes, they serialize the datas and then they should 
> make a new object with those datas):
> Serializer (an interface, every class which need serialization must be 
> derived from this, however this is only a marker, it will be not 
> serialized)
> RenderableSerializer : public Serializer - this isn't pure virtual 
> however shouldn't be never serialized directly (since the object made 
> by this class is a pure virtual one) -  These will use the tag 
> <renderable>
> SkyboxSerializer : public RenderableSerializer - these will use the 
> tag <skybox>
> EntitySerializer : public Serializer - these will use the tag <entity>
> many other classes will be added in future and they'll all derive form 
> RenderableSerializer.
>
>
> Now the problem is EntitySerializer have a pointer to a 
> RenderableSerializer and when I serialize EntitySerializer the pointer 
> to that class is considered to be a RenderableSerializer and not the 
> derived class. I don't know at priori which class is the base class 
> and this lead to problem.
> If I serialize a SkyboxSerializer I have the correct tag: a <skybox> 
> which have inside a <renderable> and the datas are correct.
> If I try to serialize an Entity I had a lot of problem, mostly just 
> make the library crash. As I've seen in the tutorial I should register 
> all the derived classes before pass the pointer to the Archive. I did 
> it registering the SkyboxSerializer classes but it lead to a wrong 
> xml: a correct <entity> tag which have a correct <skybox> with all 
> it's data but also a wrong <renderable> tag which have inside the same 
> data of the tag <skybox> instead of the data of a RenderableSerializer 
> class.
>
> Now the question is: is there a correct way to use the library this 
> way? With a pointer to a base class of which the derived is not known?
> My code is too big and I made many attempt to use the library so I'm 
> not posting it in this message. If you need it I will post it.
> Thank you for your replies.
>
>
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It seems no one know the answer. I hope it's just I made a too vague 
request. Here's the partial code (load function are implemented the same 
way, simmetrically):
EntitySerializer.hpp:
void *save*(xml_oarchive& ar, const unsigned int version) const
{
     ar << make_nvp("EntityName", _nome); // string
     ar.register_type(static_cast<SkyBoxSerializer *>(NULL)); // Note: 
this is just for debug, in the future I'll make a function in every 
class derived from Serializer which register itself when needed.
     ar << make_nvp(_renderable->getTagName().c_str(), _renderable);
}

SkyboxSerializer.hpp:
void *save*(xml_oarchive& ar, const unsigned int version) const
{
     ar << make_nvp("renderable",
         boost::serialization::base_object< RenderableSerializer >(*this));
     //RenderableSerializer::save(ar, version); // If I use this line 
instead of the previous it de/serializer correctly but I know this is a 
dirty work-around and I want to avoid it.
     ar << make_nvp("shader_file", _fx_file); // std::string
     ar << make_nvp("mesh_file", _mesh_filename); // std::string
     ar << make_nvp("cubemap_file", _tex_filename); // std::string
}
RenderableSerialier.hpp:
void *save*(xml_oarchive& ar, const unsigned int version) const
{
     ar << make_nvp("scala", _scala); // struct vector
     ar << make_nvp("rotazione", _rotazione); // struct vector
     ar << make_nvp("posizione", _posizione); // struct vector
}
VectorSerializer.hpp:
struct vettore
{
float x, y, z;
};

namespace boost
{
namespace serialization
     {
template<class Archive> void *serialize*(Archive& ar, vettore& vec, 
const unsigned int version)
         {
             ar & make_nvp("x", vec.x);
             ar & make_nvp("y", vec.y);
             ar & make_nvp("z", vec.z);
         }
     }
}

Serializer.hpp:
virtual void *save*(xml_oarchive& ar, const unsigned int version) const = 0;

And this is the xml resultant:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<!DOCTYPE boost_serialization>
<boost_serialization signature="serialization::archive" version="7">
<entity class_id="0" tracking_level="0" version="0">
<EntityName>skybohx</EntityName>
<skybox class_id="1" tracking_level="1" version="0" object_id="_0">
<renderable class_id="2" tracking_level="1" version="0" object_id="_1">
<renderable object_id_reference="_1"></renderable>
<shader_file>skybox.fx</shader_file>
<mesh_file>asd.x</mesh_file>
<cubemap_file>CubeMap.dds</cubemap_file>
</renderable>
<shader_file>skybox.fx</shader_file>
<mesh_file>asd.x</mesh_file>
<cubemap_file>CubeMap.dds</cubemap_file>
</skybox>
</entity>
</boost_serialization>

As you can see the renderable tag inside the skybox tag is wrong. The 
<renderable> should have:
<scala>
<x>3</x>
<y>3</y>
<z>3</z>
</scala>
<rotazione>
<x>2</x>
<y>2</y>
<z>2</z>
</rotazione>
<posizione>
<x>1</x>
<y>1</y>
<z>1</z>
</posizione>

Why that tag serialize the derived class instead of itself?
Thank you again for your answers.