VersionPress\Database\EntityInfo::isVirtualReference PHP Method

    public function isVirtualReference($reference)
    {
        return isset($this->virtualReferences[$reference]);
    }

 private function fixMnReferences()
 {
     $referencesToSave = $this->getExistingMnReferences();
     $vpIdsToLoad = $this->getAllVpIdsUsedInReferences($referencesToSave);
     $idMap = $this->getIdsForVpIds($vpIdsToLoad);
     $hasAllIds = $this->idMapContainsAllVpIds($idMap, $vpIdsToLoad);
     if (!$hasAllIds) {
         return false;
     }
     foreach ($referencesToSave as $reference => $relations) {
         if ($this->entityInfo->isVirtualReference($reference)) {
             continue;
         }
         $referenceDetails = ReferenceUtils::getMnReferenceDetails($this->dbSchema, $this->entityName, $reference);
         $prefixedTable = $this->database->prefix . $referenceDetails['junction-table'];
         $sourceColumn = $referenceDetails['source-column'];
         $targetColumn = $referenceDetails['target-column'];
         $valuesForInsert = array_map(function ($relation) use($idMap) {
             $sourceId = $idMap[$relation['vp_id']];
             $targetId = $idMap[$relation['referenced_vp_id']];
             return "({$sourceId}, {$targetId})";
         }, $relations);
         $sql = sprintf("SELECT id FROM %s WHERE HEX(vp_id) IN ('%s')", $this->database->vp_id, join("', '", array_map(function ($entity) {
             return $entity['vp_id'];
         }, $this->entities)));
         $processedIds = array_merge($this->database->get_col($sql), $this->deletedIds);
         if ($this->isSelectiveSynchronization) {
             if (count($processedIds) > 0) {
                 $this->database->query("DELETE FROM {$prefixedTable} WHERE {$sourceColumn} IN (" . join(", ", $processedIds) . ")");
             }
         } else {
             $this->database->query("TRUNCATE TABLE {$prefixedTable}");
         }
         $valuesString = join(", ", $valuesForInsert);
         $insertSql = "INSERT IGNORE INTO {$prefixedTable} ({$sourceColumn}, {$targetColumn}) VALUES {$valuesString}";
         $this->database->query($insertSql);
     }
     return true;
 }