code: private function getParentRelationshipWithoutCache($tableName)
      {
          $table = $this->getSchema()->getTable($tableName);
          foreach ($table->getForeignKeys() as $fk) {
              if ($this->isInheritanceRelationship($fk)) {
                  return $fk;
              }
          }
  
          return;
      }
docs: If this table is pointing to a parent table (if its primary key is a foreign key pointing on another table),
  this function will return the pointed table.
  This function will return null if there is no parent table.
  
  @param string $tableName
  
  @return ForeignKeyConstraint|null