How to Create Models in your Django Application

Django Overview

Django is a web development framework for developing dynamic websites and applications. Django allows the use of less code and eases the creation of complex websites. It provides a very good structure and easy methods that help to do the heavy lifting when writing web applications.

To follow this tutorial, we assume that you completed successfully the first tutorial on Django installation and configuration.

Requirements:
You completed the Django installation and configuration tutorial
You have an account and are logged into console.scaleway.com
You have configured your SSH Key
You have sudo privileges or access to the root user
You have a server running on Ubuntu Focal Fossa (20.04 LTS).

Creating Models

Now that your environment (my-django) is set up, we can create a new application. The difference between an application and a project is that an app is a Web application that does something. A project is a collection of configuration and apps for a particular Web site. A project can contain multiple apps. An app can be in multiple projects.

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

python manage.py startapp polls

We will create two models: Question and Choice. A Question has a question and a publication date. A Choice has two fields: the text of the choice and a vote tally. Each Choice is associated with a Question.

2 . Edit the polls/models.py file so it looks like this

from django.db import models

# Create your models here.
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)

3 . To activate the app, edit the myDjangoProject/settings.py file again

nano myDjangoProject/settings.py

4 . Change the INSTALLED_APPS setting to include the string polls

# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'polls',
]

5 . Run makemigrations to indicate Django that you’ve made some changes to your models

python manage.py make migrations polls

which returns

Migrations for 'polls':
  polls/migrations/0001_initial.py
    - Create model Choice
    - Create model Question
    - Add field question to choice

Note: You can read the migration for your new model if you like; it’s the file polls/migrations/0001_initial.py

6 . Run the migrations with the migrate command to manage your database schema automatically

python manage.py migrate

which returns

Operations to perform:
  Apply all migrations: admin, auth, contenttypes, polls, sessions
Running migrations:
  Applying polls.0001_initial... OK

The migrate command takes all the migrations that have not been applied and runs them against your database, synchronizing the changes you made to your models with the schema in the database.

Playing with the API

1 . Invoke the Python shell

python manage.py shell

2 . Paste the following content to the shell

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

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

# 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 your name?", pub_date=timezone.now())

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

# Now it has an ID. Note that this might say "1L" instead of "1", depending
# on which database you're using.
>>> q.id
1

# Access model field values via Python attributes.
>>> q.question_text
"What's your name?"
>>> q.pub_date
datetime.datetime(2018, 10, 31, 10, 54, 26, 985783, tzinfo=<UTC>)

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

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

Exit the Python shell by pressing Control+D.

3 . Edit the polls/models.py to add a __str__() method to both Question and Choice.

Note: The str() method is called whenever you call str() on an object. In Python 3, Django uses str(obj) in a number of places. Most notably, to display an object in the Django admin site and as the value inserted into a template when it displays an object.

nano polls/models.py

and paste

from django.db import models

# Create your models here.
from django.db import models


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

    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

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

python manage.py shell

and paste the following to make sure our __str__() addition worked.

>>> from polls.models import Question, Choice

>>> Question.objects.all()
[<Question: What's your name?>]

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

# Request an ID that doesn't exist, this will raise an exception.
>>> Question.objects.get(id=3)
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 your name?>

Rendering the Application visible in the Console

1 . When youre logged in, the poll app is not displayed on the admin console. To make it appear, edit the polls/admin.py to match the following:

from django.contrib import admin

from .models import Question

admin.site.register(Question)

2 . Reload the Admin Console and login.

python manage.py runserver your_server_ip:8000

You now have several questions on your admin interface.

If you click on Question, it displays the list of questions we added to the configuration file.

Click on each question to either edit or delete it.

Adding Related Objects

Now that we have the questions on the admin page we need to configure the multiple choices response.

1 . Edit the polls/admin.py to add the following

from django.contrib import admin

from .models import Choice, Question

admin.site.register(Choice)

2 . Reload the Admin Console and login.

python manage.py runserver your_server_ip:8000

You now have Choice displayed on your admin interface.

3 . You can add as many choices as you wish. Click on Choices to add a choice.

4 . Select your question and type your answer.

You now have a poll with questions and answers. If you want to customize your interface, follow the official Django documentation.