Notes on Django

Django.md

1. Create an empty django migration

python manage.py makemigrations --empty yourappname

2. Show applied migrations

python manage.py showmigrations <app_name>

3. Rollback migration to a specific state

python manage.py migrate <app_name> <desired_migration_state.py>

4. Delete all objects in the table

Post.objects.all().delete()

5. Filter rows where a field is not null

Post.objects.filter(title__isnull=False)

6. Use first instead of get so it returns None if it does not exist

post = Post.objects.filter(id=1).first()

7. Count the foreign key elements.

Post.objects.annotate(num_articles=Count('article')).filter(num_articles__gt=1)

8. Solving circular imports

• prefer import Library vs from Library import SomeObject
• Better: field = models.ForeignKey('app.SomeObject', on_delete=models.CASCADE), instead of specifying the class itself, you can pass a string

Articles

1. Designing better models

• https://simpleisbetterthancomplex.com/tips/2018/02/10/django-tip-22-designing-better-models.html

2. Testing emails sent

• https://www.programcreek.com/python/example/60241/django.core.mail.outbox
• https://simpleisbetterthancomplex.com/questions/2017/07/07/mocking-emails.html