Athena Developer Guide

Athena Chapter 7 Accessing data Version/Issue: 2.0.0
• Put some instructions (i.e. options) into the job option file (see Listing 7.7)
• Register your object in the store us usual, typically in the execute() method of your
algorithm.
// myAlg implementation file
StatusCode myAlg::execute() {
// Create a UDO object and register it into the event data store
UDO* p = new UDO();
eventSvc->registerObject(“/Event/myStuff/myUDO”, p);
}
In order to actually trigger the conversion and saving of the objects at the end of the current event
processing it is necessary to inform the application manager. This requires some options to be specified
in the job options file:
Listing 7.7 Job options for output to persistent storage
ApplicationMgr.OutStream = { "DstWriter" };
DstWriter.ItemList
DstWriter.EvtDataSvc
DstWriter.Output
= { "/Event#1", "/Event/MyTracks#1"};
= "EventDataSvc";
= "DATAFILE='result.root' TYP='ROOT'";
ApplicationMgr.DLLs
+= { "DbConverters", "RootDb"};
ApplicationMgr.ExtSvc += { "DbEventCnvSvc/RootEvtCnvSvc" };
EventPersistencySvc.CnvServices += { "RootEvtCnvSvc" };
RootEvtCnvSvc.DbType
= "ROOT";
The first option tells the application manager that you wish to create an output stream called
“DstWriter”. You may create as many output streams as you like and give them whatever name you
prefer.
For each output stream object which you create you must set several properties. The ItemList option
specifies the list of paths to the objects which you wish to write to this output stream. The number after
the “#” symbol denotes the number of directory levels below the specified path which should be
traversed. The (optional) EvtDataSvc option specifies in which transient data service the output
stream should search for the objects in the ItemList, the default is the standard transient event data
service EventDataSvc. The Output option specifies the name of the output data file and the type of
persistency technology, ROOT in this example. The last three options are needed to tell the Application
manager to instantiate the RootEvtCnvSvc and to associate the ROOT persistency type to this
service.
An example of saving data to a ROOT persistent data store is available in the RootIO example
distributed with the framework.
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