code: private void onRelation(Object entity, Map<String, Object> relationsMap, final Relation relation,
              final EntityMetadata metadata, final PersistenceDelegator pd, boolean lazilyloaded,
              Map<Object, Object> relationStack)
      {
          final Object entityId = PropertyAccessorHelper.getId(entity, metadata);
  
          // if relation map contains value, then invoke target entity with find
          // by id.
          // else invoke target entity for find by relation, pass it's entityId as
          // a column value and relation.getJoinColumnName as column name.
  
          Object relationValue = relationsMap != null ? relationsMap.get(relation.getJoinColumnName(kunderaMetadata))
                  : null;
          EntityMetadata targetEntityMetadata = KunderaMetadataManager.getEntityMetadata(kunderaMetadata,
                  relation.getTargetEntity());
  
          List relationalEntities = fetchRelations(relation, metadata, pd, entityId, relationValue, targetEntityMetadata);
  
          if (relationalEntities != null)
          {
  
              for (Object relationEntity : relationalEntities)
              {
                  if (relationEntity != null)
                  {
                      addToRelationStack(relationStack, relationEntity, targetEntityMetadata);
                  }
              }
              for (Object relationEntity : relationalEntities)
              {
                  if (relationEntity != null)
                  {
                      onParseRelation(entity, pd, targetEntityMetadata, relationEntity, relation, lazilyloaded,
                              relationStack);
                      PersistenceCacheManager.addEntityToPersistenceCache(getEntity(relationEntity), pd,
                              PropertyAccessorHelper.getId(relationEntity, targetEntityMetadata));
                  }
              }
          }
  
      }
docs: Method to handle one to one association relation events.
  
  @param entity
  relation owning entity.
  @param entityId
  entity id of relation owning entity.
  @param relationsMap
  contains relation name and it's value.
  @param relationStack
  @param m
  entity metadata.