Athena Developer Guide

Athena
Chapter 15 Converters Version/Issue: 2.0.0
The instantiation of the appropriate converter is done by a macro. The macro instantiates also the
converter factory used to instantiate the requested converter. Hence, all other user code is shielded from
the implementation and definitions of the ROOT specific code.
Listing 15.2 Implementing a “generic” converter for the transient class Event.
1: // Include files
2: #include "GaudiKernel/ObjectVector.h"
3: #include "GaudiKernel/ObjectList.h"
4: #include "GaudiDb/DbGenericConverter.h"
5: // Converter implementation for objects of class Event
6: #include "Event.h"
7: _ImplementConverter(Event)
The macro needs a few words of explanation: the instantiated converters are able to create transient
objects of type Event. The corresponding persistent type is of a generic type, the data are stored as a
machine independent byte stream. It is mandatory that the Event class implements a streamer method
“serialize”. An example from the Event class of the RootIO example is shown in Listing 15.3.
The instantiated converter is of the type DbGenericConverter and the instance of the instantiating
factory has the instance name DbEventCnvFactory.
Listing 15.3 Serialisation of the class Event.
1: /// Serialize the object for writing
2: virtual StreamBuffer& serialize( StreamBuffer& s ) const {
3: DataObject::serialize(s);
4: return s
5: > m_run
15: >> m_time;
16: }
15.7.1 Non Identifiable Objects
Non identifiable objects cannot directly be retrieved/stored from the data store. Usually they are small
and in any case they are contained by a container object. Examples are particles, hits or vertices. These
classes can be converted using a generic container converter. Container converters exist currently for
lists and vectors. The containers rely on the serialize methods of the contained objects. The serialisation
is able to understand smart references to other objects within the same data store. Listing 15.4 shows an
example of the serialize methods of the MyTrack class of the RootIO example
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