public function getRelationTable()
    {
        if (is_null($this->relationTable)) {
            $parentTable = $this->getParentTableName();
            $table = $this->getEntityDescriptor()->getTableName();
            $names = [$parentTable, $table];
            asort($names);
            $first = array_shift($names);
            $tableName = $this->normalizeFieldName($first);
            array_unshift($names, $tableName);
            $this->relationTable = implode('_', $names);
        }
        return $this->relationTable;
    }