source/Spiral/ORM/Entities/Relations/AbstractRelation.php
protected function primaryColumnOf(RecordInterface $record): string
    {
        return $this->orm->define(get_class($record), ORMInterface::R_PRIMARY_KEY);
    }
protected function primaryColumnOf(RecordInterface $record): string
    {
        return $this->orm->define(get_class($record), ORMInterface::R_PRIMARY_KEY);
    }
protected function primaryColumnOf ( RecordInterface $ record ) : string { return $ this -> orm -> define ( get_class ( $ record ) , ORMInterface :: R_PRIMARY_KEY ) ; }
Get primary key column

@param RecordInterface $record

@return string
Get primary key column