Some Tips on Django ORM

django_orm_tips_sub_query.py

# Django ORM Tips:

# When you have do an SQL"IN" operation, we generally do it like this. ie, convert the results to a list.
# DON'T DO THIS
seasons = list(Season.objects.values_list('name', flat=True))
result = Crops.objects.filter(season__name__in=seasons)
print(result)

# The above ORM query will generate the following SQL command:
# SELECT * FROM crops c inner join season s on c.season_id = s.id where s.name in ('winter', 'summer', ...)

# As you can see this will call the database 2 time. 1st when we ran the list() conversion and then on the print() operation.


# INSTED USE THIS, BECAUSE ORM CONVERT THIS INTO A SUB-QUERY WHICH WILL DO THE SAME THING IN JUST ONE QUERY
# SELECT * FROM crops c inner join season s on c.season_id = s.id where s.name in (SELECT name FROM season)
seasons = Season.objects.values_list('name', flat=True)
result = Crops.objects.filter(season__name__in=seasons)