Writing your first Django app, part 1

Let’s learn by example.

Throughout this tutorial, we’ll walk you through the creation of a basic poll application.

It’ll consist of two parts:

A public site that lets people view polls and vote in them.

An admin site that lets you add, change, and delete polls.

We’ll assume you have Django installed already. You can tell Django is installed and which version by running the following command in a shell prompt (indicated by the $ prefix):

...\> py -m django --version

If Django is installed, you should see the version of your installation. If it isn’t, you’ll get an error telling “No module named django”.

This tutorial is written for Django 5.1, which supports Python 3.10 and later

Creating a project

From the command line, cd into a directory where you’d like to store your code and create a new directory named djangotutorial. (This directory name doesn’t matter to Django; you can rename it to anything you like.)

...\> mkdir Django-tutorial

Then, run the following command to bootstrap a new Django project:

...\> django-admin startproject mysite Django-tutorial

This will create a project called mysite inside the djangotutorial directory. If it didn’t work, see Problems running django-admin.

Let’s look at what startproject created:

djangotutorial/
    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        asgi.py
        wsgi.py

These files are:

manage.py: A command-line utility that lets you interact with this Django project in various ways. You can read all the details about manage.py in django-admin and manage.py.

mysite/: A directory that is the actual Python package for your project. Its name is the Python package name you’ll need to use to import anything inside it (e.g. mysite.urls).

mysite/init.py: An empty file that tells Python that this directory should be considered a Python package. If you’re a Python beginner, read more about packages in the official Python docs.

mysite/settings.py: Settings/configuration for this Django project. Django settings will tell you all about how settings work.

mysite/urls.py: The URL declarations for this Django project; a “table of contents” of your Django-powered site. You can read more about URLs in URL dispatcher.

mysite/asgi.py: An entry-point for ASGI-compatible web servers to serve your project. See How to deploy with ASGI for more details.

mysite/wsgi.py: An entry-point for WSGI-compatible web servers to serve your project. See How to deploy with WSGI for more details.

The development server

Let’s verify your Django project works. Change into the djangotutorial directory, if you haven’t already, and run the following commands:

...\> py manage.py runserver

You’ll see the following output on the command line:

Performing system checks...

System check identified no issues (0 silenced).

You have unapplied migrations; your app may not work properly until they are applied.
Run 'python manage.py migrate' to apply them.

November 11, 2024 - 15:50:53
Django version 5.1, using settings 'mysite.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

Creating the Polls app

To create your app, make sure you’re in the same directory as manage.py and type this command:

...\> py manage.py startapp polls

That’ll create a directory polls, which is laid out like this:

polls/
    __init__.py
    admin.py
    apps.py
    migrations/
        __init__.py
    models.py
    tests.py
    views.py

Write your first view

Let’s write the first view. Open the file polls/views.py and put the following Python code in it:

#polls/views.py
from django.http import HttpResponse


def index(request):
    return HttpResponse("Hello, world. You're at the polls index.")

To define a URLconf for the polls app, create a file polls/urls.py with the following content:

#polls/urls.py
from django.urls import path

from . import views

urlpatterns = [
    path("", views.index, name="index"),
]

Your app directory should now look like:

polls/
    __init__.py
    admin.py
    apps.py
    migrations/
        __init__.py
    models.py
    tests.py
    urls.py
    views.py

The next step is to configure the global URLconf in the mysite project to include the URLconf defined in polls.urls. To do this, add an import for django.urls.include in mysite/urls.py and insert an include() in the urlpatterns list, so you have:

#mysites/urls.py
from django.contrib import admin
from django.urls import include, path

urlpatterns = [
    path("polls/", include("polls.urls")),
    path("admin/", admin.site.urls),
]

You have now wired an index view into the URLconf. Verify it’s working with the following command:

...\> py manage.py runserver

Writing your first Django app, part 2

Database setup

By default, the DATABASES configuration uses SQLite. If you’re new to databases, or you’re just interested in trying Django, this is the easiest choice. SQLite is included in Python, so you won’t need to install anything else to support your database. When starting your first real project, however, you may want to use a more scalable database like PostgreSQL, to avoid database-switching headaches down the road.

If you wish to use another database, see details to customize and get your database running.

While you’re editing mysite/settings.py, set TIME_ZONE to your time zone.

Also, note the INSTALLED_APPS setting at the top of the file. That holds the names of all Django applications that are activated in this Django instance. Apps can be used in multiple projects, and you can package and distribute them for use by others in their projects.

By default, INSTALLED_APPS contains the following apps, all of which come with Django:

django.contrib.admin – The admin site. You’ll use it shortly.

django.contrib.auth – An authentication system.

django.contrib.contenttypes – A framework for content types.

django.contrib.sessions – A session framework.

django.contrib.messages – A messaging framework.

django.contrib.staticfiles – A framework for managing static files.

These applications are included by default as a convenience for the common case.

Some of these applications make use of at least one database table, though, so we need to create the tables in the database before we can use them. To do that, run the following command:

...\> py manage.py migrate

The migrate command will only run migrations for apps in INSTALLED_APPS.

Creating models

#polls/models
from django.db import models


class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField("date published")


class Choice(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

Activating models

That small bit of model code gives Django a lot of information. With it, Django is able to:

• Create a database schema (CREATE TABLE statements) for this app.

• Create a Python database-access API for accessing Question and Choice objects.

But first we need to tell our project that the polls app is installed.

To include the app in our project, we need to add a reference to its configuration class in the INSTALLED_APPS setting. The PollsConfig class is in the polls/apps.py file, so its dotted path is 'polls.apps.PollsConfig'. Edit the mysite/settings.py file and add that dotted path to the INSTALLED_APPS setting. It’ll look like this:

#mysite/settings.py
INSTALLED_APPS = [
    "polls.apps.PollsConfig",
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
]

Now Django knows to include the polls app. Let’s run another command:

...\> py manage.py makemigrations polls

You should see something similar to the following:

Migrations for 'polls':
  polls/migrations/0001_initial.py
    + Create model Question
    + Create model Choice

By running makemigrations, you’re telling Django that you’ve made some changes to your models (in this case, you’ve made new ones) and that you’d like the changes to be stored as a migration.

Migrations are how Django stores changes to your models (and thus your database schema) - they’re files on disk. You can read the migration for your new model if you like; it’s the file polls/migrations/0001_initial.py. Don’t worry, you’re not expected to read them every time Django makes one, but they’re designed to be human-editable in case you want to manually tweak how Django changes things.

There’s a command that will run the migrations for you and manage your database schema automatically - that’s called migrate, and we’ll come to it in a moment - but first, let’s see what SQL that migration would run. The sqlmigrate command takes migration names and returns their SQL:

...\> py manage.py sqlmigrate polls 0001

You should see something similar to the following (we’ve reformatted it for readability):

BEGIN;
--
-- Create model Question
--
CREATE TABLE "polls_question" (
    "id" bigint NOT NULL PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
    "question_text" varchar(200) NOT NULL,
    "pub_date" timestamp with time zone NOT NULL
);
--
-- Create model Choice
--
CREATE TABLE "polls_choice" (
    "id" bigint NOT NULL PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
    "choice_text" varchar(200) NOT NULL,
    "votes" integer NOT NULL,
    "question_id" bigint NOT NULL
);
ALTER TABLE "polls_choice"
  ADD CONSTRAINT "polls_choice_question_id_c5b4b260_fk_polls_question_id"
    FOREIGN KEY ("question_id")
    REFERENCES "polls_question" ("id")
    DEFERRABLE INITIALLY DEFERRED;
CREATE INDEX "polls_choice_question_id_c5b4b260" ON "polls_choice" ("question_id");

COMMIT;

Note the following:

• The exact output will vary depending on the database you are using. The example above is generated for PostgreSQL.

• Table names are automatically generated by combining the name of the app (polls) and the lowercase name of the model – question and choice. (You can override this behavior.)

• Primary keys (IDs) are added automatically. (You can override this, too.)

• By convention, Django appends "_id" to the foreign key field name. (Yes, you can override this, as well.)

• The foreign key relationship is made explicit by a FOREIGN KEY constraint. Don’t worry about the DEFERRABLE parts; it’s telling PostgreSQL to not enforce the foreign key until the end of the transaction.

• It’s tailored to the database you’re using, so database-specific field types such as auto_increment (MySQL), bigint PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY (PostgreSQL), or integer primary key autoincrement (SQLite) are handled for you automatically. Same goes for the quoting of field names – e.g., using double quotes or single quotes.

• The sqlmigrate command doesn’t actually run the migration on your database - instead, it prints it to the screen so that you can see what SQL Django thinks is required. It’s useful for checking what Django is going to do or if you have database administrators who require SQL scripts for changes.

If you’re interested, you can also run python manage.py check; this checks for any problems in your project without making migrations or touching the database.

Now, run migrate again to create those model tables in your database:

...\> py manage.py sqlmigrate

The migrate command takes all the migrations that haven’t been applied (Django tracks which ones are applied using a special table in your database called django_migrations) and runs them against your database - essentially, synchronizing the changes you made to your models with the schema in the database.

Migrations are very powerful and let you change your models over time, as you develop your project, without the need to delete your database or tables and make new ones - it specializes in upgrading your database live, without losing data. We’ll cover them in more depth in a later part of the tutorial, but for now, remember the three-step guide to making model changes:

• Change your models (in models.py).

• Run python manage.py makemigrations to create migrations for those changes

• Run python manage.py migrate to apply those changes to the database.

The reason that there are separate commands to make and apply migrations is because you’ll commit migrations to your version control system and ship them with your app; they not only make your development easier, they’re also usable by other developers and in production.

Read the django-admin documentation for full information on what the manage.py utility can do.

Playing with the API

Now, let’s hop into the interactive Python shell and play around with the free API Django gives you. To invoke the Python shell, use this command:

...\> py manage.py shell

We’re using this instead of simply typing “python”, because manage.py sets the DJANGO_SETTINGS_MODULE environment variable, which gives Django the Python import path to your mysite/settings.py file.

Once you’re in the shell, explore the database API:

>>> from polls.models import Choice, Question  # Import the model classes we just wrote.

# No questions are in the system yet.
>>> Question.objects.all()
<QuerySet []>

# Create a new Question.
# Support for time zones is enabled in the default settings file, so
# Django expects a datetime with tzinfo for pub_date. Use timezone.now()
# instead of datetime.datetime.now() and it will do the right thing.
>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())

# Save the object into the database. You have to call save() explicitly.
>>> q.save()

# Now it has an ID.
>>> q.id
1

# Access model field values via Python attributes.
>>> q.question_text
"What's new?"
>>> q.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=datetime.timezone.utc)

# Change values by changing the attributes, then calling save().
>>> q.question_text = "What's up?"
>>> q.save()

# objects.all() displays all the questions in the database.
>>> Question.objects.all()
<QuerySet [<Question: Question object (1)>]>

Wait a minute. <Question: Question object (1)> isn’t a helpful representation of this object. Let’s fix that by editing the Question model (in the polls/models.py file) and adding a str() method to both Question and Choice:

#polls/models
from django.db import models


class Question(models.Model):
    # ...
    def __str__(self):
        return self.question_text


class Choice(models.Model):
    # ...
    def __str__(self):
        return self.choice_text

It’s important to add str() methods to your models, not only for your own convenience when dealing with the interactive prompt, but also because objects’ representations are used throughout Django’s automatically-generated admin.

Let’s also add a custom method to this model:

#polls/models.py
import datetime

from django.db import models
from django.utils import timezone


class Question(models.Model):
    # ...
    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

Note the addition of import datetime and from django.utils import timezone, to reference Python’s standard datetime module and Django’s time-zone-related utilities in django.utils.timezone, respectively. If you aren’t familiar with time zone handling in Python, you can learn more in the time zone support docs.

Save these changes and start a new Python interactive shell by running python manage.py shell again:

>>> from polls.models import Choice, Question

# Make sure our __str__() addition worked.
>>> Question.objects.all()
<QuerySet [<Question: What's up?>]>

# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
>>> Question.objects.filter(id=1)
<QuerySet [<Question: What's up?>]>
>>> Question.objects.filter(question_text__startswith="What")
<QuerySet [<Question: What's up?>]>

# Get the question that was published this year.
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Question.objects.get(pub_date__year=current_year)
<Question: What's up?>

# Request an ID that doesn't exist, this will raise an exception.
>>> Question.objects.get(id=2)
Traceback (most recent call last):
    ...
DoesNotExist: Question matching query does not exist.

# Lookup by a primary key is the most common case, so Django provides a
# shortcut for primary-key exact lookups.
# The following is identical to Question.objects.get(id=1).
>>> Question.objects.get(pk=1)
<Question: What's up?>

# Make sure our custom method worked.
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True

# Give the Question a couple of Choices. The create call constructs a new
# Choice object, does the INSERT statement, adds the choice to the set
# of available choices and returns the new Choice object. Django creates
# a set (defined as "choice_set") to hold the "other side" of a ForeignKey
# relation (e.g. a question's choice) which can be accessed via the API.
>>> q = Question.objects.get(pk=1)

# Display any choices from the related object set -- none so far.
>>> q.choice_set.all()
<QuerySet []>

# Create three choices.
>>> q.choice_set.create(choice_text="Not much", votes=0)
<Choice: Not much>
>>> q.choice_set.create(choice_text="The sky", votes=0)
<Choice: The sky>
>>> c = q.choice_set.create(choice_text="Just hacking again", votes=0)

# Choice objects have API access to their related Question objects.
>>> c.question
<Question: What's up?>

# And vice versa: Question objects get access to Choice objects.
>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> q.choice_set.count()
3

# 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)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>

# Let's delete one of the choices. Use delete() for that.
>>> c = q.choice_set.filter(choice_text__startswith="Just hacking")
>>> c.delete()

For more information on model relations, see Accessing related objects. For more on how to use double underscores to perform field lookups via the API, see Field lookups. For full details on the database API, see our Database API reference.

Creating an admin user

First we’ll need to create a user who can login to the admin site. Run the following command:

...\> py manage.py createsuperuser

Enter your desired username and press enter.

Username: admin

You will then be prompted for your desired email address:

Email address: admin@example.com

The final step is to enter your password. You will be asked to enter your password twice, the second time as a confirmation of the first.

Password: **********
Password (again): *********
Superuser created successfully.

Start the development server¶

The Django admin site is activated by default. Let’s start the development server and explore it.

If the server is not running start it like so:

...\> py manage.py runserver

Now, open a web browser and go to “/admin/” on your local domain – e.g., http://127.0.0.1:8000/admin/. You should see the admin’s login screen:

Since translation is turned on by default, if you set LANGUAGE_CODE, the login screen will be displayed in the given language (if Django has appropriate translations).

Enter the admin site

Now, try logging in with the superuser account you created in the previous step. You should see the Django admin index page:

You should see a few types of editable content: groups and users. They are provided by django.contrib.auth, the authentication framework shipped by Django.

Make the poll app modifiable in the admin

But where’s our poll app? It’s not displayed on the admin index page.

Only one more thing to do: we need to tell the admin that Question objects have an admin interface. To do this, open the polls/admin.py file, and edit it to look like this:

#polls/admin.py
from django.contrib import admin

from .models import Question

admin.site.register(Question)

Explore the free admin functionality

Now that we’ve registered Question, Django knows that it should be displayed on the admin index page:

Click “Questions”. Now you’re at the “change list” page for questions. This page displays all the questions in the database and lets you choose one to change it. There’s the “What’s up?” question we created earlier:

Click the “What’s up?” question to edit it:

Things to note here:

• The form is automatically generated from the Question model.

• The different model field types (DateTimeField, CharField) correspond to the appropriate HTML input widget. Each type of field knows how to display itself in the Django admin.

• Each DateTimeField gets free JavaScript shortcuts. Dates get a “Today” shortcut and calendar popup, and times get a “Now” shortcut and a convenient popup that lists commonly entered times.

• The bottom part of the page gives you a couple of options:

• Save – Saves changes and returns to the change-list page for this type of object.

• Save and continue editing – Saves changes and reloads the admin page for this object.

• Save and add another – Saves changes and loads a new, blank form for this type of object.

• Delete – Displays a delete confirmation page.

If the value of “Date published” doesn’t match the time when you created the question in Tutorial 1, it probably means you forgot to set the correct value for the TIME_ZONE setting. Change it, reload the page and check that the correct value appears.

Change the “Date published” by clicking the “Today” and “Now” shortcuts. Then click “Save and continue editing.” Then click “History” in the upper right. You’ll see a page listing all changes made to this object via the Django admin, with the timestamp and username of the person who made the change:

When you’re comfortable with the models API and have familiarized yourself with the admin site, read part 3 of this tutorial to learn about how to add more views to our polls app.