code: private void addLinkValue(String targetObjID) {
          int targetShardNo = getTargetObjectShardNumber(targetObjID);
          if (targetShardNo > 0 && m_linkDef.isSharded()) {
              m_dbTran.addShardedLinkValue(m_dbObj.getObjectID(), m_linkDef, targetObjID, targetShardNo);
          } else {
              m_dbTran.addLinkValue(m_dbObj.getObjectID(), m_linkDef, targetObjID);
          }
          addInverseLinkValue(targetObjID);
      }
docs: Add mutations to add a reference via our link to the given target object ID.