Django多个对象的ForeignKey
我正在创建一个应用程序，用户可以订阅或关注网站的不同内容。
我正在建立一个表格，用来记录所有这些订阅。我的初步想法是做一个订阅表，这个表会列出所有被订阅的内容。现在我的计划是这样的：
class SubscriptionTypeCode(object):
CITY = '1'
REGION = '2'
COUNTRY = '3'
USER = '4'
SUBSCRIPTION_TYPE_CHOICES = (
(SubscriptionTypeCode.CITY, 'City'),
(SubscriptionTypeCode.REGION, 'Region'),
(SubscriptionTypeCode.COUNTRY, 'Country'),
(SubscriptionTypeCode.USER, 'User'),
)
class Subscription(models.Model):
subscriber = models.ForeignKey(User, related_name="subscriber")
subscription_type = models.CharField(max_length=4, choices=SUBSCRIPTION_TYPE_CHOICES)
subscription_to_user = models.ForeignKey(User, related_name="subscription_to_user", null=True, blank=True)
subscription_to_city = models.ForeignKey(City, null=True, blank=True)
subscription_to_country = models.ForeignKey(Country, null=True, blank=True)
subscription_to_region = models.ForeignKey(Region, null=True, blank=True)
created = models.DateTimeField(db_index=True, auto_now_add=True)
cancelled = models.DateTimeField(null=True, blank=True)
这个方法应该是可行的，但我在想这样做是否是最有效的方式。每一行都会有一个订阅者的ID，然后是类型选择，接着根据这个选择，某个订阅到的列会有一个外部对象。
这个方法是有效的，但在逻辑上需要很多if/else语句。例如：
def create_subscription(request, subscription_type, subscription_id):
subscription = Subscription.create(
subscriber = request.user,
subscription_type = subscription_type,
)
if subscription_type == SubscriptionTypeCode.REGION:
region = get_region(subscription_id)
subscription.subscription_to_region = region
elif subscription_type == SubscriptionTypeCode.CITY:
city = get_city(subscription_id)
subscription.subscription_to_city = city
elif subscription_type == SubscriptionTypeCode.COUNTRY:
country = get_country(subscription_id)
subscription.subscription_to_country = country
elif subscription_type == SubscriptionTypeCode.USER:
user = get_user(subscription_id)
subscription.subscription_to_user = user
subscription.save()
return subscription
你们有什么想法可以简化这个吗？或者这样做可以吗？