void CBallotRelSet::Open(const CDistrict* district, const CBaseunit* baseunit, 
                          const CVGroup* vgroup1, const CVGroup* vgroup2)
{
   ASSERT(m_pDB != NULL);
   ASSERT(m_pDB->IsOpen());
   ASSERT(GetSize() == 0);
   ASSERT(district != NULL);
   ASSERT(baseunit != NULL);
   if (district->KeyId() == -1) {
      Open(baseunit, vgroup1);
   } else {
      const CDistrictItem* pDistrictItem = m_pDB->Find(*district);
      if (pDistrictItem != NULL) {
         const CBaseunitKeyTable& baseunitTable = 
                                       pDistrictItem->m_BaseunitKeyTable;
         int count = baseunitTable.GetSize();
         for (int i = 0; i < count; i++) {
            const CBaseunit& curBaseunit = baseunitTable.GetAt(i);
            if (baseunit->KeyId() == -1 || *baseunit == curBaseunit) {
               const CBallotRelationshipItem* pBalRelItem = NULL;
               while ((pBalRelItem = m_pDB->FindNextBalRel(curBaseunit, 
                                                            pBalRelItem))){
                  if (!vgroup1 || vgroup1->KeyId() == -1 ||
                     (*vgroup1 == pBalRelItem->m_VGroup1 && !vgroup2) ||
                     (vgroup2 && *vgroup2 == pBalRelItem->m_VGroup2 &&
                        *vgroup1 == pBalRelItem->m_VGroup1))
                     Add(pBalRelItem);
              }
         }
     }
     m_CurIndex = 0;
     m_Open = TRUE;
   }
 }
}

Figure 2: The function CBallotRelSet::Open from TSElection/TSElectionSet.cpp. This complex function is completely undocumented.