Django ORM tips&tricks demo app

This application was created to present database schema and allow trying out concepts from Django ORM tips&tricks presentation from wroc.py meetup on June 2, 2020.

How to use

Follow steps below and you will be ready to go.

Setup

Application is dockerized, to run it make sure that you have Docker and docker-compose installed and configured properly.

It uses some environment variables loaded from .envs/ directory, please create following file structure:

.envs
└── .local
    ├── .django
    └──  .postgres

Add following minimal content to them:

1. .envs/.local/.django

# PostgreSQL
POSTGRES_HOST=db
POSTGRES_PORT=5432
CONN_MAX_AGE=60

# General settings
DJANGO_READ_DOT_ENV_FILE=False
DJANGO_SETTINGS_MODULE=config.settings.local

# Settings module for tests
DJANGO_SETTINGS_MODULE_TEST=config.settings.test
DJANGO_SECRET_KEY=gL/s)op}&Fky9*&B{p1^]ewfW~xsP.#DV+kDj{Ne>/Pv<kPVTU
DJANGO_ALLOWED_HOSTS=*

# Celery, Redis cache
CELERY_BROKER_URL=redis://redis:6379
REDIS_URL=redis://redis:6379
CELERY_FLOWER_USER=flower_user
CELERY_FLOWER_PASSWORD=flower_password

2. .envs/.local/.postgres

# PostgreSQL
POSTGRES_DB=backend
POSTGRES_USER=backend
POSTGRES_PASSWORD=backend

Build

Run in projects root directory:

$ docker-compose build

Setup the database tables:

$ docker-compose run --rm app ./manage.py migrate

Run

To startup the application run

$ docker-compose up

You can then use it like regular Django application (but you shouldn't as there is nothing more than the database schema defined in this app).

Play

To try out the queries and see the SQL representation run Django shell with:

$ docker-compose run --rm app ./manage.py shell

In the shell execute following commands:

from orm_blog.blog.models import BlogPost, Author, Category, Comment
from django.db import connection, reset_queries

Now you have access to the app's Django Models and you can monitor queries (make sure that DEBUG setting is True, which is the default when running locally).

You can execute queries and check the raw SQL executed with:

# execute query
BlogPost.objects.values("title")
# print queries
connection.queries
# to reset queries list run
reset_queries()  

Full shell execution look like following:

In [2]: from orm_blog.blog.models import BlogPost, Author, Category, Comment           

In [3]: from django.db import connection, reset_queries                                

In [4]: BlogPost.objects.values("title")                                               
Out[4]: <QuerySet []>

In [5]: connection.queries                                                             
Out[5]: 
[{'sql': 'SELECT "blog_blogpost"."title" FROM "blog_blogpost" LIMIT 21',
  'time': '0.005'}]

In [6]: reset_queries()                                                                

In [7]: connection.queries                                                             
Out[7]: []