I am trying to understand the most efficient way to query the data needed from multiple tables in Django.
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")
How can I optimize the query below to get the city this student belongs to?
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)
You can query with:
City.objects.get(address__student=mystudent)This will produce a query that looks like:
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