How to reduce the number of calls to the database?select_related?

Question

How to reduce the number of calls to the database?select_related?

Do I understand correctly that:

cat = Category.objects.get(id=1)
In the template
cat.children.all()
cat.children.all()
cat.children.all()
cat.children.all()

There will be 4 calls to the database, and if so:

cat = Category.objects.select_related().get(id=1)
in the template
cat.children.all()
cat.children.all()
cat.children.all()
cat.children.all()

one or the other? Or am I mistaken?

shani asked July 9th 19 at 13:31

More answers about "How to reduce the number of calls to the database?select_related?"

2 answers

Willow17 answered on July 9th 19 at 13:35

Look at prefetch_related.

samir39 answered on · Accepted Answer · 2019-07-09T13:33:20.936Z

Wrong. In the first case there will be two treatment - getting the category when calling Category.objects.get(id=1) and getting its child elements on the first invocation of cat.children.all(), and all subsequent calls will be taken from the cache ORM. In the second select_related() will be ignored, as it is used for joins s, and you have children, most likely records from the same table. select_related() helps when you need to read the two related models in one query. This is all very straightforward and in detail described in the documentation.

Helps enlightenment view of sql queries after you are done queryset'AMI:

from django.db import connection
print(connection.queries)

Allows you to understand and how many of them were made, and what specific.