장고 쿼리 뿌시기

Lazy Evaluation

• Django ORM doesn't make the SQL calls until the data is actually needed

Query Expressions

• https://docs.djangoproject.com/en/3.2/ref/models/expressions/

Database Functions

• https://docs.djangoproject.com/en/3.2/ref/models/database-functions/

db_index

db_index=True

• https://docs.djangoproject.com/en/3.2/ref/models/indexes/
• https://docs.djangoproject.com/en/3.2/ref/models/options/#indexes
• https://blog.myungseokang.dev/posts/database-access-optimization/

언제 index를 걸어야할까?

• 처음부터 index를 이용할 필요는 없다. 필요가 보이면 건다.
• index를 거는 것을 고려해야하는 경우들:
  * 전체 쿼리에 10-25%를 차지하는 경우
  • real data가 있는 경우, 인덱싱의 결과를 분석할 수 있음
  • index가 결과에 도움을 주는 지 테스트를 해볼 수 있음

Transactions

• The default behavior of the ORM is to autocommit every query when it is called.
• The disadvantage if that if a view (or some other operation) requires two or more database modifications to occur, if one modification succeeds and the other fails, the database is at risk of corruption.
• The way to resovle the risk of database corruption is through the use of database transactions.

database transaction

• where two or more database updates are contained in a single unit of work

atomic_requests

# settings/base.py

DATABASES = {
	'default': {
    	# ...
        'ATOMIC_REQUESTS': True,
    },
}

• https://wayhome25.github.io/django/2017/08/01/tsd7-django-query-database2/
• http://schoolofweb.net/blog/posts/%EB%82%98%EC%9D%98-%EC%B2%AB-django-%EC%95%B1-%EB%A7%8C%EB%93%A4%EA%B8%B0-part-4-1/

wrapping each HTTP request in a transaction

# flavors/views.py

from django.db import transaction
from django.http import HttpResponse
from django.shortcuts import get_object_or_404
from django.utils import timezone

from .models import Flavor


@transaction.non_atomic_requests
def posting_flavor_status(request, pk, status):
	flavor = get_object_or_404(Flavor, pk=pk)
    
    # this will execute in autocommit mode (Django's default).
    flavor.latest_status_change_attempt = timezone.now()
    flavor.save()
    
    with transaction.atomic():
    	# this code executes inside a transaction
        flavor.status = status
        flavor.latest_status_change_success = timezone.now()
        flavor.save()
        return HttpResponse('Hooray')
    
    # if the transaction fails, return the appropriate status
    return HttpResponse('Sadness', status_code=400)

• https://docs.djangoproject.com/en/3.2/topics/db/transactions/
• https://realpython.com/transaction-management-with-django-1-6/

Reference

• https://github.com/feldroy/two-scoops-of-django-3.x
• 책/Two Scoops of Django 3.x