public function delete($entityId, $col = 'id')
    {
        if (is_null($entityId)
            || (!is_numeric($entityId) && !is_a($entityId, $this->entityClass))) {
            throw new \InvalidArgumentException(
                "Invalid entity or entityId argument."
            );
        }

        if ($entityId instanceof $this->entityClass) {
            $entityId = $entityId->id;
        }

        return $this->adapter->delete($this->entityTable, "$col = $entityId");
    }