Django §

The de facto full stack Python web framework. In addition to libraries Django comes with CLI tools to manage your projects. The getting started docs for Django can be found here:

https://www.djangoproject.com/start/

Django Project Organization §

Django projects are generally structured in the following way. The Django project itself is the outermost layer. The Django project the contains the basic settings necessary to run your project and connect the Django apps that it contains. Inside a Django project there can be one or many Django apps. Each Django app may contain it’s own set of models, templates, URLs, and more. When Django apps are designed properly so that they live within themselves they can be more easily shared between projects. In this way the Django ecosystem allows for plugins to be distributed as Django apps to include in your larger Django project similar to the way WordPress plugins and templates work. Django apps and Django projects are both created from the Django CLI tools as documented below.

Common Django CLI commands §

# install django
pip install django
 
# Check your Django version: 
 
$ python -m django --version
 
# Create a new project: 
 
django-admin startproject mysite
 
# Run your project:
 
python manage.py runserver
 
# Run the Django API explorer in the python REPL
 
python manage.py shell
 
# Create an app inside your project
 
python manage.py startapp myappname
 
# Run database migrations
 
python manage.py migrate
 
# Make migrations for your app
 
python manage.py makemigrations myappname
 
# Check migrations for problems before applying them
 
python manage.py check
 
# Apply your migrations
 
python manage.py migrate
 
# Create your admin user 
 
python manage.py createsuperuser

Commonly modified in settings.py §

 
INSTALLED_APPS = [
    "myapp.apps.MyConfig",
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
]
 
# ~ ~ ~ ~ 
 
TIME_ZONE = "America/New_York"

Django Databases & ORM §

Django uses an Object Relational Mapper (ORM) and a standardized models.py file associated with each app to CREATE the necessary tables for the app automatically. A deep understanding of the models class is necessary to use this effectively but allows your database to be relatively agnostic between SQLite, Postgres, etc.

The docs for the ORM in 5.0 can be found here:

https://docs.djangoproject.com/en/5.0/topics/db/models/

Django Field Name Restrictions §

Naming your fields in Django requires you to follow two rules.

1. You may not name a field a python reserved word. You can see the list of reserved python words by running help("keywords") in the Python REPL. As of Python 3.12.3 the reserved words are: and, as, assert, async, await, break, class, continue, def, del, elif, else, except, False, finally, for, from, global, if, import, in, is, lambda, None, nonlocal, not, or, pass, raise, return, True, try, while, with, yield
2. Your field name may not contain double underscores anywhere in it’s name.

Updating your models in 3-5 steps §

Remember the 3-4 steps for making and adjusting models…

1. Change your models (in models.py).
2. Run python manage.py makemigrations to create migrations for those changes
3. Optionally run python manage.py check to check for problems.
4. Run python manage.py migrate to apply those changes to the database.
5. Update the admin interface model in admin.py if necessary

Django Database Relationships §

The most important relationship to understand how to specify are many-to-one, many-to-many and one-to-one.

https://docs.djangoproject.com/en/5.0/topics/db/models/#relationships

many-to-one use models.ForeignKey many-to-many use models.ManyToManyField one-to-one use models.OneToOneField

Building models from an existing database §

If you have an existing database design you have built out and wish to integrate with Django there is a Django utility called inspectdb that will generate the models from an existing database.

Querying Django Collections with the ORM §

Django offers object methods like filter, get, and all. These methods take keyword arguments like filter(id=4). Django offers a shortcut to use the primary key via pk so in a table where id was the primary filter(pk=4) would be the equivalent. This could he handy I suppose, though I generally prefer verbosity over shortcuts, especially in a case where the primary key is already a 2 character id.

Here are some sample queries for the Django shell REPL.

from polls.models import Choice, Question
from django.utils import timezone
 
Question.objects.all()
 
q = Question(question_text="What's new?", pub_date=timezone.now())
 
q.save()
 
q.id
 
q.question_text
 
q.pub_date
 
q.question_text = "What's up?"
 
q.save()
 
Question.objects.all()
 
Question.objects.filter(id=1)
 
q = Question.objects.get(pk=1)
 
current_year = timezone.now().year
Question.objects.get(pub_date__year=current_year)
 
Question.objects.get(id=2) # this should throw an error
 
Question.objects.filter(question_text__startswith="What")
 
q.choice_set.all()
 
q.choice_set.create(choice_text="Not much", votes=0)
q.choice_set.create(choice_text="The sky", votes=0)
c = q.choice_set.create(choice_text="Just hacking again", votes=0)
c.question()
 
  
# The API automatically follows relationships as far as you need.
# Use double underscores to separate relationships.
# This works as many levels deep as you want; there's no limit.
# Find all Choices for any question whose pub_date is in this year
# (reusing the 'current_year' variable we created above).
Choice.objects.filter(question__pub_date__year=current_year)
 
 
# Let's delete one of the choices. Use delete() for that.
c = q.choice_set.filter(choice_text__startswith="Just hacking")
c.delete()
 

Sample models.py §

import datetime
 
from django.db import models
from django.utils import timezone
 
# Create your models here.
 
 
class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField("date published")
 
    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)
 
    def __str__(self):
        return self.question_text
 
 
class Choice(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)
 
    def __str__(self):
        return self.choice_text
   

Django Shortcuts §

Django has several shortcuts for doing commonly repeated tasks like rendering a template or generating a 404 when a matching object isn’t found.

render §

The following functions are equivalent…

  
def index(request):
    latest_question_list = Question.objects.order_by("-pub_date")[:5]
    template = loader.get_template("polls/index.html")
    context = {
        "latest_question_list": latest_question_list,
    }
    return HttpResponse(template.render(context, request))
    
def index(request):
    latest_question_list = Question.objects.order_by("-pub_date")[:5]
    context = {"latest_question_list": latest_question_list}
    return render(request, "polls/index.html", context)

get_object_or_404 §

The following functions are equivalent…

def detail(request, question_id):
    try:
        question = Question.objects.get(pk=question_id)
    except Question.DoesNotExist:
        raise Http404("Question does not exist")
    return render(request, "polls/detail.html", {"question": question})
 
 
def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, "polls/detail.html", {"question": question})

Django Namespaces & Templates §

Namespacing your URLs §

To namespace your URLs add an app_name line before your url_patterns = [ line in urls.py

app_name = "polls"
url_patterns = [
...

Proper linking §

Use the url method to have django traverse your URLconf to properly link to another view. This allows you to modify the path of a view without needing to update any links manually.

Bad

<li><a href="/polls/{{ question.id }}/">{{ question.question_text }}</a></li>

Better

<li><a href="{% url 'detail' question.id %}">{{ question.question_text }}</a></li>

Best

<li><a href="{% url 'polls:detail' question.id %}">{{ question.question_text }}</a></li>