如何在django中查询多个模型

Question

我试图了解查询Django中多个表所需数据的最有效方法。

class City():
name = models.CharlField()
class Address():
line1 = models.CharlField()
...
city_id = models.ForeignKey(City, ... related_name="city_address")
class Student()
name = models.CharlField()
gender = models.CharlField()
# a student can only have one address
address_id = models.OneToOneField(Address, ... related_name="address_student")

我如何优化下面的查询来获得这个学生所属的城市?

student = Student.objects.filter(name="John").first() # assuming its a unique name
address_id = student.address_id
address = Address.objects.filter(id=address).first()
city_id = address.city_id
City.objects.get(id=city_id)

Answer 1

可以使用以下命令查询:

City.objects.get(address__student=mystudent)

这将产生如下查询:

SELECT city.*
FROM city
INNER JOIN address ON address.city_id_id = city.id
INNER JOIN student ON student.address_id_id = address.id
WHERE student.id =id_of_the_student