Django Tips

REPL driven development

In addition to working with Django admin for testing, you can also get REPL access to your Django environment:

$ python manage.py shell

and do things like test out how to access or filter a model, etc

Same with the db env:

$ python manage.py dbshell

Migrations

See migations with showmigrations:

$ python manage.py showmigrations

Or create a migation:

$ python manage.py makemigration

Migrate with migrate, or roll back a migration by referencing the migration before it for the given section:

$ pythom manage.py migrate core 002_migation_to_rollback_to

A migration that involves additional processing such as a backfill can also be done. Create an empty migration and then use RunPython:

from django.db import migrations

def run_backfill(apps, schema_editor):
    MyModel = apps.get_model('core', 'MyModel')
    db_alias = schema_editor.connection.alias
    model = MyModel.objects.using(db_alias).get(...)
    ...

class Migration(migations.Migration):
    dependencies = [
        ('core', '003_backfill')
    ]

    operations = [
        migrations.RunPython(run_backfill)
    ]

Performance

• Cache reused template objects with {% with ... %}

• Use select_related and prefetch_related to prefetch results from joined tables that will be reused in the view template:

  result = Hangout.select_related('hangout__owner')
        .select_related('hangout__owner__profile')
        .filter(hangout=request.user.hangout)

• Django also has some extra support for relational data, such as union, intersection and difference:

  queryset1.union(queryset2)
  queryset1.intersection(queryset2)
  queryset1.difference(queryset2)

• Use .query on queryset objects to debug the actual SQL statement that's generated.

  • Ex: debugging GROUP BY SQL created with .annotate

Serving production static files

• Production static files are collected with python manage.py collectstatic

• Django's default settings for static files is typically enough for most use cases, but there are times when it makes sense to code something in non-dev mode, such as when customizing error pages

• Make the STATIC_URL property customizable in settings.py:

  STATIC_URL = os.getenv('DJANGO_STATIC_URL') or '/static/'

• An easy to way to serve them is with http-server:

  $ npm i -g http-server
  $ http-server staticfiles/
  $ DJANGO_STATIC_URL=localhost:8080 python manage.py runserver