我一直认为在Django中链接多个filter()调用和将它们收集到单个调用中是相同的。
# Equivalent
Model.objects.filter(foo=1).filter(bar=2)
Model.objects.filter(foo=1,bar=2)
但我在我的代码中遇到了一个复杂的查询集,情况并非如此。
class Inventory(models.Model):
book = models.ForeignKey(Book)
class Profile(models.Model):
user = models.OneToOneField(auth.models.User)
vacation = models.BooleanField()
country = models.CharField(max_length=30)
# Not Equivalent!
Book.objects.filter(inventory__user__profile__vacation=False).filter(inventory__user__profile__country='BR')
Book.objects.filter(inventory__user__profile__vacation=False, inventory__user__profile__country='BR')
生成的SQL语句为:
SELECT "library_book"."id", "library_book"."asin", "library_book"."added", "library_book"."updated" FROM "library_book" INNER JOIN "library_inventory" ON ("library_book"."id" = "library_inventory"."book_id") INNER JOIN "auth_user" ON ("library_inventory"."user_id" = "auth_user"."id") INNER JOIN "library_profile" ON ("auth_user"."id" = "library_profile"."user_id") INNER JOIN "library_inventory" T5 ON ("library_book"."id" = T5."book_id") INNER JOIN "auth_user" T6 ON (T5."user_id" = T6."id") INNER JOIN "library_profile" T7 ON (T6."id" = T7."user_id") WHERE ("library_profile"."vacation" = False AND T7."country" = BR )
SELECT "library_book"."id", "library_book"."asin", "library_book"."added", "library_book"."updated" FROM "library_book" INNER JOIN "library_inventory" ON ("library_book"."id" = "library_inventory"."book_id") INNER JOIN "auth_user" ON ("library_inventory"."user_id" = "auth_user"."id") INNER JOIN "library_profile" ON ("auth_user"."id" = "library_profile"."user_id") WHERE ("library_profile"."vacation" = False AND "library_profile"."country" = BR )
第一个使用链式 filter()
调用的查询集在 Inventory 模型上进行了两次连接,有效地创建了两个条件之间的 OR 关系,而第二个查询集将这两个条件 AND 在一起。我原本以为第一次查询也会将这两个条件 AND 在一起。这是 Django 的预期行为还是一个 bug?相关问题的答案 “在 Django 中使用“.filter().filter().filter()...”是否有缺点? 似乎表明这两个查询集应该是等价的。