Django模型manytomany過濾器

Question

可以說我有用戶，通訊和訂閱模型，訂閱是用戶和時事通訊的映射表，例如。認購有外鍵，用戶和通訊

class User(models.Model): 
    ... 

class Newsletter(models.Model): 
    ... 

class Subscription(models.Model): 
    subscriber = models.ForeignKey(User) 
    newsletter = models.ForeignKey(Newsletter) 

我如何查詢集返回時事特定用戶已經在一個非常簡單的查詢訂閱？我覺得有一個，但不能真正想到它，除非通過多個陳述來實現這一點。

Answer 1

這應該工作：

Newsletter.objects.filter(
    id__in=[subscription.newsletter.id for subscription in 
      Subscription.objects.filter(subscriber=user)] 

更可讀（和冗長的）版本：

subscriptions = Subscription.objects.filter(subscriber=user) # all subscriptions for a given user 

newsletter_ids = [subscription.newsletter.id for subscription in subscriptions] 

Newsletter.objects.filter(id__in=newsletter_ids) # answer