在Django中，如何获取一个模型的所有实例，而与fk的第一个模型相关的另一个模型的实例不存在？

Question

This is really tricky to me. I have the following models:

class Item(models.Model):
      title = models.CharField(max_length=150)
      item_type = models.CharField(choices=item_choices)

class Suggestion(models.Model):
      user = models.ForeignKey(User)
      item = models.ForeignKey(Item)

I need to get all the items of a given item_type that don't have a suggestion related to it and to a given user. Can this be achieved in one query?

Many thanks!

Answer 1

This can be done with .exclude() :

items = Item.objects.filter(item_type=item_type).exclude(suggestion__user=user)

This follows the backwards relation to Suggestion , and the forward relation to User , and excludes any Item s where the related user matches the given user.

Answer 2

One approach is to create a queryset of items with suggestions related to the user, then use that as a subquery.

items_suggested_by_user = Item.objects.filter(suggestion__user=user)
item_types = Item.objects.filter(item_type=item_type)
items = item_types.exclude(item__in=items_suggested_by_user)