Django模型多態相關領域

Question

我試圖刪除我的Django模型中的重復代碼。 正如您在下面的代碼中看到的， send_salary_notification和send_pension_notifications之間的唯一區別是，一個使用相關的字段jurisdiction ，另一個使用agency 。 我如何重構代碼，以便根據record_type設置管轄區/代理商一次？

我嘗試創建一個類變量作為record_type ，並在第一個函數中設置變量cls.record_type = record_type ，然后這個：

agencies_changed.append(subscription.record_type)

但是這給出了一個錯誤，即record_type不是有效的實例。

這是我的代碼：

class Subscriber(models.Model):
    email = models.EmailField(null=False, unique=True)
    activation_key = models.CharField(max_length=64)
    key_expires = models.DateTimeField(default=get_key_expiration)
    verified = models.BooleanField(default=False)

    @classmethod
    def send_notifications(cls, record_type, slugs):
        """
        Sends notifications for all subscribers.
        """
        subscribers = cls.objects.all()
        for subscriber in subscribers:
            if record_type == 'salary':
                subscriber.send_salary_notifications(slugs, record_type)
            elif record_type == 'pension':
                subscriber.send_pension_notifications(slugs, record_type)

    def send_salary_notifications(self, slugs, record_type):
        matching_subscriptions = self.get_matching_salary_subscriptions(slugs)
        agencies_changed = []

        if not matching_subscriptions:
            return None

        for subscription in matching_subscriptions:
            agencies_changed.append(subscription.jurisdiction)
            self.update_salary_last_year_sent(subscription)

        message = self.build_notification_message(agencies_changed, record_type)
        self.send_notification_email(message)

    def send_pension_notifications(self, slugs, record_type):
        matching_subscriptions = self.get_matching_pension_subscriptions(slugs)
        agencies_changed = []

        if not matching_subscriptions:
            return None

        for subscription in matching_subscriptions:
            agencies_changed.append(subscription.agency)
            self.update_pension_last_year_sent(subscription)

        message = self.build_notification_message(agencies_changed, record_type)
        self.send_notification_email(message)


class SalarySubscription(models.Model):
    subscriber = models.ForeignKey('subscriptions.Subscriber', related_name='salary_subscriptions')
    jurisdiction = models.ForeignKey('jurisdiction.Jurisdiction')
    last_year_sent = models.PositiveSmallIntegerField(null=True)


class PensionSubscription(models.Model):
    subscriber = models.ForeignKey('subscriptions.Subscriber', related_name='pension_subscriptions')
    agency = models.ForeignKey('pensions.Agency')
    last_year_sent = models.PositiveSmallIntegerField(null=True)

Answer 1

假設您不想更改get_matching_pension_subscriptions ， get_matching_salary_subscriptions ， update_salary_last_year_sent和update_pension_last_year_sent方法，則可以將代碼重構為以下內容。 您可以使用getattr builtin動態定義單個通知方法並獲取相關屬性，具體取決於record_type 。 可能有其他重構解決方案更適合您的代碼庫，但看到您發布此解決方案的代碼片段非常合理。

class Subscriber(models.Model):
    @classmethod
    def send_notifications(cls, record_type, slugs):
        """
        Sends notifications for all subscribers.
        """
        subscribers = cls.objects.all()
        for subscriber in subscribers:
            subscriber._send_notification(record_type, slugs)

    def _send_notification(self, record_type, slugs):
        matching_subscriptions = getattr(self, 'get_matching_{}_subscriptions'.format(record_type))(slugs)
        if not matching_subscriptions:
            return None

        agencies_changed = []
        agency_attribute = {
            'salary': 'jurisdiction',
            'pension': 'agency'
        }[record_type]

        for subscription in matching_subscriptions:
            agencies_changed.append(getattr(subscription, agency_attribute))
            getattr(self, 'update_{}_last_year_sent'.format(record_type))(subscription)

        message = self.build_notification_message(agencies_changed, record_type)
        self.send_notification_email(message)