Compare fields within relationship on Django ORM - django

Question

I have two models, route and stop.
A route can have several stop, each stop have a name and a number. On same route, stop.number are unique.
The problem:
I need to search which route has two different stops and one stop.number is less than the other stop.number
Consider the following models:
class Route(models.Model):
name = models.CharField(max_length=20)
class Stop(models.Model):
route = models.ForeignKey(Route)
number = models.PositiveSmallIntegerField()
location = models.CharField(max_length=45)
And the following data:
Stop table
| id | route_id | number | location |
|----|----------|--------|----------|
| 1 | 1 | 1 | 'A' |
| 2 | 1 | 2 | 'B' |
| 3 | 1 | 3 | 'C' |
| 4 | 2 | 1 | 'C' |
| 5 | 2 | 2 | 'B' |
| 6 | 2 | 3 | 'A' |
In example:
Given two locations 'A' and 'B', search which routes have both location and A.number is less than B.number
With the previous data, it should match route id 1 and not route id 2
On raw SQL, this works with a single query:
SELECT
`route`.id
FROM
`route`
LEFT JOIN `stop` stop_from ON stop_from.`route_id` = `route`.`id`
LEFT JOIN `stop` stop_to ON stop_to.`route_id` = `route`.`id`
WHERE
stop_from.`stop_location_id` = 'A'
AND stop_to.`stop_location_id` = 'B'
AND stop_from.stop_number < stop_to.stop_number
Is this possible to do with one single query on Django ORM as well?

Answer 1

Generally ORM frameworks like Django ORM, SQLAlchemy and even Hibernate is not design to autogenerate most efficient query. There is a way to write this query only using Model objects, however, since I had similar issue, I would suggest to use raw query for more complex queries. Following is link for Django raw query:
[https://docs.djangoproject.com/en/1.11/topics/db/sql/]
Although, you can write your query in many ways but something like following could help.
from django.db import connection
def my_custom_sql(self):
with connection.cursor() as cursor:
cursor.execute("SELECT
`route`.id
FROM
`route`
LEFT JOIN `stop` stop_from ON stop_from.`route_id` = `route`.`id`
LEFT JOIN `stop` stop_to ON stop_to.`route_id` = `route`.`id`
WHERE
stop_from.`stop_location_id` = %s
AND stop_to.`stop_location_id` = %s
AND stop_from.stop_number < stop_to.stop_number", ['A', 'B'])
row = cursor.fetchone()
return row
hope this helps.