TruthMetaDataWriter.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/

// TruthMetaDataWriter.cxx
// Author: James Catmore (James.Catmore@cern.ch)
 
// Header for this class
#include "TruthMetaDataWriter.h"
 
// EDM Objects that we need
#include "xAODTruth/TruthMetaData.h"
#include "xAODTruth/TruthMetaDataAuxContainer.h"
 
#include "StoreGate/ReadHandle.h"
 
// For accessing the tagInfo
#include "AthenaPoolUtilities/CondAttrListCollection.h"
 
// Athena initialize and finalize
StatusCode DerivationFramework::TruthMetaDataWriter::initialize()
{
    ATH_MSG_VERBOSE("initialize() ...");
 
    ATH_CHECK( m_eventInfoKey.initialize() );
 
    // Initialize the service handles
    CHECK( m_metaStore.retrieve() );
    CHECK( m_weightSvc.retrieve() );
    CHECK( m_tagInfoMgr.retrieve() );
 
    // Create an empty truth meta data container:
    xAOD::TruthMetaDataAuxContainer* aux = new xAOD::TruthMetaDataAuxContainer();
    m_tmd = new xAOD::TruthMetaDataContainer();
    m_tmd->setStore( aux );
    // Record it in the metadata store
    CHECK( m_metaStore->record( aux, m_metaName + "Aux." ) );
    CHECK( m_metaStore->record( m_tmd, m_metaName ) );
 
    return StatusCode::SUCCESS;
}
 
// Selection and collection creation
StatusCode DerivationFramework::TruthMetaDataWriter::addBranches(const EventContext& ctx) const
{
 
    //The mcChannelNumber is used as a unique identifier for which truth meta data belongs to
    uint32_t mcChannelNumber = 0;
    // If this fails, we are running on a datatype with no EventInfo.  Such data types should
    //  definitely not be mixing MC samples, so this should be safe (will fall back to 0 above)
    SG::ReadHandle<xAOD::EventInfo> eventInfo(m_eventInfoKey, ctx);
    if (eventInfo.isPresent()) {
      mcChannelNumber = eventInfo->mcChannelNumber();
    }
 
    //Inserting in a (unordered_)set returns an <iterator, boolean> pair, where the boolean
    //is used to check if the key already exists (returns false in the case it exists)
    if( m_existingMetaDataChan.insert(mcChannelNumber).second ) {
        xAOD::TruthMetaData* md = new xAOD::TruthMetaData();
        m_tmd->push_back( md );
 
        // Get the list of weights from the metadata
        std::map<std::string,std::size_t> weight_name_map = m_weightSvc->weightNames(ctx);
 
        std::vector<std::string> orderedWeightNameVec;
        orderedWeightNameVec.reserve( weight_name_map.size() );
        for (auto& entry: weight_name_map) {
            orderedWeightNameVec.push_back(entry.first);
        }
 
        //The map from the HepMC record pairs the weight names with a corresponding index,
        //it is not guaranteed that the indices are ascending when iterating over the map
        std::sort(orderedWeightNameVec.begin(), orderedWeightNameVec.end(),
                  [&](const std::string& i, const std::string& j){return weight_name_map.at(i) < weight_name_map.at(j);});
 
        md->setMcChannelNumber(mcChannelNumber);
        md->setWeightNames( orderedWeightNameVec );

        md->setLhefGenerator( m_tagInfoMgr->findTag("lhefGenerator") );
        md->setGenerators( m_tagInfoMgr->findTag("generators") );
        md->setEvgenProcess( m_tagInfoMgr->findTag("evgenProcess") );
        md->setEvgenTune( m_tagInfoMgr->findTag("evgenTune") );
        md->setHardPDF( m_tagInfoMgr->findTag("hardPDF") );
        md->setSoftPDF( m_tagInfoMgr->findTag("softPDF") );
        // Done getting things from the TagInfo
 
    } // Done making the new truth metadata object
    return StatusCode::SUCCESS;
}